16
Delivered by Publishing Technology to: Guest User IP: 41.217.203.183 on: Fri, 07 Nov 2014 13:34:51 Copyright (c) Nevin Scrimshaw International Nutrition Foundation. All rights reserved. S524 Food and Nutrition Bulletin, vol. 28, no. 4 (supplement) © 2007, The United Nations University. Iron metabolism and malaria Abstract Recent evidence from a large, randomized, controlled trial has suggested that the universal administration of iron to children in malaria-endemic areas is associated with an increase in adverse health outcomes. The pur- pose of this paper is to summarize the available ecologic and intervention trials related to iron and malaria in children, and to set these against current knowledge of the biology of host–pathogen interactions involving iron metabolism. We conclude that, although not fully consist- ent, the balance of evidence confirms that administration of iron (usually in combination with folic acid) increases the incidence of malaria when given without prophylaxis and in the absence of universal access to treatment. The mechanisms by which additional iron can benefit the par- asite are far from clear. There is evidence to suggest that the apparent detrimental effect of iron supplementation may vary according to levels of antecedent iron status, the presence of hemoglobinopathies and glucose-6-phosphate dehydrogenase (G6PD) deficiency, and other host genetic variants, such as variants in haptoglobin. The effects of malaria on host iron metabolism are also reviewed and reveal that the key cause of malaria-induced anemia is a maldistribution of iron and suppression of erythropoiesis rather than an exacerbation of gross iron deficiency. We tentatively conclude that, if it is to be recommended, uni- versal iron supplementation in malarious areas should only be considered in conjunction with some form of prophylaxis (e.g., intermittent preventive therapy [IPT]) or in the context of good health services with ready access to facilities for malaria diagnosis and treatment. An alternative approach would be to screen for anemia and target supplementation only to anemic children. With regard to treatment, there is good evidence that iron supplementation should be withheld until the treatment schedule is complete, both because iron may inhibit treat- ment and because the absorption of oral iron is blocked by the inflammatory response. Key words: Anemia, erythropoiesis, hemoglobin, iron, malaria, supplementation Introduction Iron-deficiency anemia remains highly prevalent glo- bally, particularly in areas of the world where malaria morbidity and mortality rates are high. The success of programs to prevent and control anemia depends on an integrated strategy to treat its underlying etiologies [1]. One of the constraints to such an approach has been the conflicting evidence from research on the relationship between iron and malaria. This persistent uncertainty is testimony to the complexity of the links between body iron status, iron supplementation, and susceptibility to malaria and other infections [2]. This paper covers five topics that together should help clarify some of these uncertainties, though our final conclusion is that significant further research will be required in order to establish a more secure evidence base for future global policy on iron administration. First, we review observational and intervention studies that have examined whether alterations in iron status affect susceptibility to malaria. Second, we summarize the effects of malaria infection on host iron metabo- lism. Third, we examine how the malaria parasite acquires and metabolizes iron. Fourth, we examine possible interactions between host hemoglobin vari- ants and susceptibility to malaria infection, both in the absence and in the presence of supplemental iron. Finally, we examine the evidence that other host genetic variants in pathways involved in iron metabolism may Andrew M. Prentice, Hala Ghattas, Conor Doherty, and Sharon E. Cox Andrew M. Prentice, Hala Ghattas, and Sharon E. Cox are affiliated with the MRC International Nutrition Group, London School of Hygiene and Tropical Medicine, London; Andrew M. Prentice and Conor Doherty are affiliated with MRC Keneba, The Gambia. Please address queries to the corresponding author: A. M. Prentice, MRC International Nutrition Group, London School of Hygiene and Tropical Medicine, Keppel Street, London SW1E 7HT, United Kingdom; e-mail: Andrew. [email protected].

Iron metabolism and malaria

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Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S524 Food and Nutrition Bulletin vol 28 no 4 (supplement) copy 2007 The United Nations University

Iron metabolism and malaria

Abstract

Recent evidence from a large randomized controlled trial has suggested that the universal administration of iron to children in malaria-endemic areas is associated with an increase in adverse health outcomes The pur-pose of this paper is to summarize the available ecologic and intervention trials related to iron and malaria in children and to set these against current knowledge of the biology of hostndashpathogen interactions involving iron metabolism We conclude that although not fully consist-ent the balance of evidence confirms that administration of iron (usually in combination with folic acid) increases the incidence of malaria when given without prophylaxis and in the absence of universal access to treatment The mechanisms by which additional iron can benefit the par-asite are far from clear There is evidence to suggest that the apparent detrimental effect of iron supplementation may vary according to levels of antecedent iron status the presence of hemoglobinopathies and glucose-6-phosphate dehydrogenase (G6PD) deficiency and other host genetic variants such as variants in haptoglobin The effects of malaria on host iron metabolism are also reviewed and reveal that the key cause of malaria-induced anemia is a maldistribution of iron and suppression of erythropoiesis rather than an exacerbation of gross iron deficiency We tentatively conclude that if it is to be recommended uni-versal iron supplementation in malarious areas should only be considered in conjunction with some form of prophylaxis (eg intermittent preventive therapy [IPT]) or in the context of good health services with ready access to facilities for malaria diagnosis and treatment An

alternative approach would be to screen for anemia and target supplementation only to anemic children With regard to treatment there is good evidence that iron supplementation should be withheld until the treatment schedule is complete both because iron may inhibit treat-ment and because the absorption of oral iron is blocked by the inflammatory response

Key words Anemia erythropoiesis hemoglobin iron malaria supplementation

Introduction

Iron-deficiency anemia remains highly prevalent glo-bally particularly in areas of the world where malaria morbidity and mortality rates are high The success of programs to prevent and control anemia depends on an integrated strategy to treat its underlying etiologies [1] One of the constraints to such an approach has been the conflicting evidence from research on the relationship between iron and malaria This persistent uncertainty is testimony to the complexity of the links between body iron status iron supplementation and susceptibility to malaria and other infections [2]

This paper covers five topics that together should help clarify some of these uncertainties though our final conclusion is that significant further research will be required in order to establish a more secure evidence base for future global policy on iron administration First we review observational and intervention studies that have examined whether alterations in iron status affect susceptibility to malaria Second we summarize the effects of malaria infection on host iron metabo-lism Third we examine how the malaria parasite acquires and metabolizes iron Fourth we examine possible interactions between host hemoglobin vari-ants and susceptibility to malaria infection both in the absence and in the presence of supplemental iron Finally we examine the evidence that other host genetic variants in pathways involved in iron metabolism may

Andrew M Prentice Hala Ghattas Conor Doherty and Sharon E Cox

Andrew M Prentice Hala Ghattas and Sharon E Cox are affiliated with the MRC International Nutrition Group London School of Hygiene and Tropical Medicine London Andrew M Prentice and Conor Doherty are affiliated with MRC Keneba The Gambia

Please address queries to the corresponding author A M Prentice MRC International Nutrition Group London School of Hygiene and Tropical Medicine Keppel Street London SW1E 7HT United Kingdom e-mail Andrewprenticelshtmacuk

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S525Iron metabolism and malaria

affect the ironndashmalaria interaction

Observational studies linking iron status and malaria

Early observations in famine environments described the suppression of malaria in severely malnourished populations and its recrudescence in those that sub-sequently consumed iron-rich diets as compared with iron-deficient diets [3] Observational studies that fol-lowed on the effect of iron status on susceptibility to malaria in moderately malnourished populations are summarized in table 1

These studies present a conflicting picture in which raised iron status was associated with increased [4 5] decreased [6] and neutral [7] effects on the subsequent risk of malaria Two studies point toward an increased susceptibility in individuals with high iron stores as measured by serum ferritin levels [4 7] but serum fer-ritin is affected by the acute phase response and is sig-nificantly correlated with markers of inflammation [8] thus making such associations particularly vulnerable to confounding Inconsistencies between study results

may also derive from differences in proportions of indi-viduals with hemoglobinopathies which can confound the relationship between iron status and malaria [9]

Iron supplementation and the risk of malaria

Iron supplementation has been the most widely used approach in the public health attempts to prevent and treat anemia Early studies of the effect of oral iron supplementation on the risk of malaria often found increases in adverse malarial outcomes in supple-mented groups [10 11] as have studies of intramuscu-lar [12] and parenteral [13] iron administration More recent studies however largely report nonsignificant effects of iron supplementation on malaria outcomes [14ndash18] (table 2) Three meta-analyses have also been conducted and are listed in table 3

The trials of iron supplementation in malaria-endemic areas are heterogeneous in dose duration and timing of supplementation age group studied hematological and malariometric inclusion criteria and outcomes assessed These design differences may

TABLE 1 Observational studies

First author Source and year Study design Findings

Oppenheimer[12]

Trans R Soc Trop Med Hyg 1986

Birthndash12 mo subanalysis of placebo group of a trial of intramuscular iron dextran Papua New Guinea N = 212

Infants with Hb gt 137 gdL and Hb gt 157 gdL at birth were 2ndash3 times more likely to have a malaria-positive slide at 12 mo

(This population has high rates of single-deletion α-thalassemia which causes anemia and protects against malaria and is therefore a potential confounder)

Snow[7]

Trans R Soc Trop Med Hyg 1991

1ndash8 yr observational study of premalaria season iron status and subsequent malaria morbidity Gambia N = 317

Susceptibility to malaria was not correlated with preseason serum iron serum iron-binding capacity or serum ferritin

Children who had a clinical attack of malaria with high levels of parasitemia tended to have higher mean serum ferritin levels at baseline

Shipton [6]

MSc dissertation London School of Hygiene and Tropical Medicine 2004 (unpublished)

6ndash36 mo retrospective clinic records Gambia N = 1072

Anemic children were marginally more suscep-tible to malaria than nonanemic children

Children who were iron supplemented were not more susceptible to malaria

Nyakeriga [4]

J Infect Dis 2004 8 mondash8 yr 2 cross-sectional surveys Kenya N = 234

Incidence of clinical malaria was lower in iron-deficient children (IRR = 07)

IRR of malaria was associated with plasma fer-ritin

Iron status markers were associated with malar-ia-specific IgGs

No difference in parasite density in patients with incident malaria between iron-deficient and non-iron-deficient groups

Hb hemoglobin IRR incidence-rate ratio IgG immunoglobulin Significant differences as reported by the authors

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S526 A M Prentice et alTa

ble

2 P

ublis

hed

tria

ls of

ora

l iro

n su

pple

men

tatio

n an

d m

alar

ia ri

sk

Firs

t aut

hor

Sour

ce a

nd y

ear

Stud

y de

sign

Mal

aria

at b

asel

ine

Iron

stat

us in

clus

ion

crite

ria

Cas

e de

tect

ion

and

trea

tmen

t of m

alar

ia

inci

dent

cas

esFi

ndin

gs

Mur

ray

[10]

BMJ 1

978

11ndash6

0 yr

sin

gle-

blin

d RC

T ir

on (9

00 m

g fe

rrou

s sul

fate

) vs

plac

ebo

N =

137

Excl

uded

par

asite

mic

su

bjec

tsH

b lt

11A

ctiv

e ca

se d

etec

tion

no

dat

a on

trea

tmen

tIn

terv

entio

n gr

oup

had

incr

ease

d H

b (3

6 g

dL

) and

tr

ansf

errin

and

incr

ease

d cl

inic

al m

alar

ia at

tack

s (O

R =

147

9)

Har

vey

[26]

Am

J Tr

op M

ed H

yg

1989

8ndash12

yr

iron

(200

mg

ferr

ous s

ulfa

te) v

s pl

aceb

o N

= 3

18

70

par

asite

mic

at

base

line

Hb

8ndash12

gd

L A

ctiv

e m

orbi

dity

re

ferr

al to

hea

lth

faci

lity

Diff

eren

ces i

n m

alar

ia p

ara-

sitem

ia at

bas

elin

e be

twee

n pl

aceb

o an

d in

terv

entio

n

mak

e fin

ding

s diff

icul

t to

inte

rpre

t0

6 g

dL d

iffer

ence

in

Hb

betw

een

grou

psPe

rcen

tage

of c

hild

ren

with

pa

rasit

emia

dec

reas

ed in

bo

th g

roup

s Pe

rcen

tage

with

pa

rasit

emia

in ir

on g

roup

re

mai

ned

high

er th

an th

at in

pl

aceb

o gr

oup

Aut

hors

con-

clud

e th

at ir

on th

erap

y ha

s no

effe

ct o

n m

alar

ia

Smith

[11]

Ann

Tro

p Pa

edia

tr

1989

6 m

ondash5

yr i

ron

(3ndash

6mg

kg fe

rrou

s su

lfate

) vs

plac

ebo

N

= 2

13

Dat

a no

t ava

ilabl

eH

b 5ndash

11 g

dL

Act

ive

mor

bidi

ty

surv

ey b

ut li

mite

d ac

cess

to m

edic

al

faci

litie

s

Iron

supp

lem

enta

tion

incr

ease

d H

b M

CV

seru

m ir

on t

rans

-fe

rrin

satu

ratio

n se

rum

fer-

ritin

In

crea

sed

feve

r ass

ocia

ted

with

pa

rasit

emia

OR

= 6

47

Chi

ppau

x [1

5]Bu

ll So

c Pat

hol E

xot

1991

6ndash36

mo

iron

(25

m

gkg

ferr

ous s

ulfa

te)

vs p

lace

bo N

= 2

20

Appr

ox 6

0 p

ara-

sitem

ic at

bas

elin

eH

b ge

8 g

dLA

ctiv

e tr

eatm

ent o

f m

alar

ia in

cide

nt c

ases

OR

for m

alar

ia-p

ositi

ve sm

ear

= 1

28 (N

S)

Law

less

[20]

J Nut

r 199

46ndash

11 y

r iro

n (1

50 m

g fe

rrou

s sul

fate

) vs

plac

ebo

N =

87

Dat

a no

t ava

ilabl

e75

h

ad H

b lt

12 g

dL

at b

asel

ine

Dat

a no

t ava

ilabl

eIr

on su

pple

men

tatio

n in

crea

sed

seru

m fe

rriti

n by

16

5 microg

L

vs p

lace

bo

No

diffe

renc

es in

pre

vale

nce

of

mal

aria

afte

r sup

plem

enta

tion

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S527Iron metabolism and malariaM

enen

dez [

23]

Tran

s R S

oc T

rop

Med

H

yg 1

994

Mul

tigra

vid

preg

nant

w

omen

iro

n (2

00 m

g fe

rrou

s sul

fate

) vs

plac

ebo

N =

550

Dat

a no

t ava

ilabl

ePC

V gt

25

Mea

n H

b =

10g

dL at

ba

selin

e

Act

ive

trea

tmen

t of

mal

aria

inci

dent

cas

esD

ecre

ased

pre

vale

nce

of

anem

ia a

nd o

f iro

n de

fi-ci

ency

Ir

on su

pple

men

tatio

n w

as n

ot

signi

fican

tly a

ssoc

iate

d w

ith

susc

eptib

ility

to p

reva

lenc

e or

se

verit

y of

mal

aria

van

Hen

sbro

ek [2

4]Tr

ans R

Soc

Tro

p M

ed

Hyg

199

56

mondash

9 yr

chl

oro-

quin

e vs

SP

+ ra

n-do

miz

atio

n to

iron

(asymp

100

mg

elem

enta

l iro

n) v

s fo

late

vs

pla-

cebo

N =

530

All

child

ren

wer

e re

crui

ted

at cl

inic

w

ith u

ncom

plic

ated

m

alar

ia

74

had

Hb

lt 11

g

dL at

bas

elin

eA

ll ch

ildre

n re

ceiv

ed

trea

tmen

t for

mal

aria

as

par

t of t

he tr

ial

Iron

gro

up h

ad m

ean

incr

ease

in

Hb

= 0

81 g

dL

Fola

te su

pple

men

tatio

n di

d no

t im

prov

e he

mat

olog

ical

pa

ram

eter

s and

incr

ease

d ra

te

of tr

eatm

ent f

ailu

re in

chil-

dren

rece

ivin

g SP

Ir

on d

id n

ot a

ffect

susc

eptib

il-ity

to m

alar

ia

Nw

anya

nwu

[17]

Ann

Tro

p M

ed P

aras

i-to

l 199

6lt

5 yr

SP

vs S

P +

daily

iron

(25

mg

kg fe

rrou

s sul

fate

) vs

SP

+ w

eekl

y iro

n

N

= 2

22

Incl

usio

n cr

iterio

n

para

site

dens

itygt

500

microl w

hole

blo

od

Hb

ge 5

gdL

All

wer

e tr

eate

d w

ith

SPD

aily

iron

+ S

P H

b in

crea

sed

49

gdL

vs

35ndash

37

gdL

in

SP a

nd S

P +

wee

kly

iron

G

reat

est b

enef

it on

Hb

in H

b gr

oup

5ndash8

gdL

at b

asel

ine

Iron

gro

ups h

ad in

crea

sed

trea

tmen

t fai

lure

vs

SP a

lone

(N

S)

van

den

Hom

berg

h [1

9]

J Tro

p Pe

diat

r 199

6lt

30 m

o ir

on (2

00

mg

ferr

ous s

ulfa

te) +

fo

late

vs

fola

te o

nly

N =

100

Onl

y in

clud

ed ch

il-dr

en w

ith p

aras

ite-

posit

ive

thic

k fil

ms

Hb

le 5

gdL

All

rece

ived

trea

tmen

t w

ith S

P +

quin

ine

40

rece

ived

blo

od tr

ans-

fusio

n

Diff

eren

ces i

n ba

selin

e ch

arac

-te

ristic

s (H

b p

aras

ite d

ensit

y be

twee

n gr

oups

)N

o sig

nific

ant d

iffer

ence

in

chan

ge in

Hb

betw

een

grou

psN

o di

ffere

nces

in m

alar

ia in

di-

ces b

etw

een

grou

ps

Men

ende

z [22

] La

ncet

199

72ndash

12 m

o ir

on (2

mg

kg fe

rrou

s gly

cine

sul-

fate

) + D

elta

prim

vs

iron

vs D

elta

prim

vs

plac

ebo

N =

832

24

of c

hild

ren

wer

e pa

rasit

emic

at b

ase-

line

PCV

gt 2

5Pa

ssiv

e ca

se d

etec

tion

plus

hig

h us

e of h

ealth

se

rvic

es

Iron

supp

lem

enta

tion

decr

ease

d an

emia

by

288

and

mal

aria

chem

opro

phy-

laxi

s dec

reas

ed a

nem

ia b

y 60

5

Iron

supp

lem

enta

tion

had

no

effe

ct o

n fr

eque

ncy

of m

alar

iaco

ntin

ued

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S528 A M Prentice et al

Berg

er [

14]

Eur J

Clin

Nut

r 200

06ndash

36 m

o iro

n (2

ndash3

mg

kg ir

on b

atai

n-at

e) v

s pl

aceb

o

N

= 1

97

62

of c

hild

ren

wer

e pa

rasit

emic

at

base

line

Hb

ge 8g

dL

Act

ive

mor

bidi

ty

follo

w-u

p an

d tr

eat-

men

t of a

ll fe

vers

w

ith a

ntim

alar

ials

Prev

alen

ce o

f iro

n-de

ficie

ncy

anem

ia d

ecre

ased

in ir

on

grou

p an

d in

crea

sed

in p

la-

cebo

gro

upA

ll m

arke

rs o

f iro

n st

atus

wer

e sig

nific

antly

hig

her i

n iro

n gr

oup

Incr

ease

in p

erce

ntag

e of

chil-

dren

with

par

asite

mia

gt 3

000

in

iron

gro

up (N

S)

Verh

oef [

18]

Lanc

et 2

002

2ndash36

mo

iron

(6 m

gkg

wk

ferr

ous f

uma-

rate

) vs

SP v

s iro

n +

SP v

s pl

aceb

o

N

= 3

28

Onl

y as

ympt

omat

ic

mal

aria

incl

uded

(3

0 d

ipst

ick

posi-

tive

at b

asel

ine)

Hb

6ndash11

gd

L A

ctiv

e fo

llow

-up

of

feve

rs a

nd tr

eatm

ent

upon

dia

gnos

is

SP a

lone

incr

ease

d H

b by

03

1 g

dLIr

on +

SP

incr

ease

d H

b by

11

1 g

dLIr

on a

lone

incr

ease

d H

b by

10

7 g

dLIn

crea

se in

mal

aria

risk

with

iro

n su

pple

men

tatio

n (N

S)

Des

ai [1

6]J I

nfec

t Dis

2003

2ndash36

mo

IPT

+ iro

n (3

ndash6 m

gkg

ferr

ous

sulfa

te) v

s iro

n vs

IP

T vs

pla

cebo

N

= 5

46

26

of c

hild

ren

wer

e pa

rasit

emic

at b

ase-

line

(are

a of

hig

h IT

N u

se

Hb

7ndash10

9 g

dL

Pass

ive

surv

eil-

lanc

e sy

stem

and

ac

tive

trea

tmen

t of

mal

aria

and

ane

mia

(4

-wee

kly

visit

s)

Iron

gro

up h

ad m

ean

incr

ease

in

Hb

of 0

88g

dL

Ir

on +

IPT

mea

n in

crea

se in

H

b =

114

gd

LIn

crea

se in

mal

aria

par

asite

mia

(N

S) H

R =

114

N

o ef

fect

on

HR

of cl

inic

al

mal

aria

Meb

raht

u [2

1]J N

utr 2

004

4ndash71

mo

iron

(10

mg

ferr

ous s

ulfa

te) v

s iro

n +

meb

enda

zole

vs

meb

enda

zole

+

plac

ebo

vs p

lace

bo

supp

lem

ente

d fo

r 12

mo

N =

614

84

of c

hild

ren

wer

e pa

rasit

emic

at

base

line

94

had

Hb

lt 11

gd

LA

ctiv

e su

rvei

llanc

e no

trea

tmen

tIn

crea

sed

seru

m fe

rriti

nD

ecre

ased

zinc

pro

topo

rphy

rin

in su

pplem

ente

d gr

oup

N

o di

ffere

nce

in m

alar

iom

etric

in

dice

s (pr

eval

ence

or p

ara-

sitem

ia)

but c

linic

al v

alue

s no

t ass

esse

d

Tabl

e 2

Pub

lishe

d tr

ials

of o

ral i

ron

supp

lem

enta

tion

and

mal

aria

risk

Firs

t aut

hor

Sour

ce a

nd y

ear

Stud

y de

sign

Mal

aria

at b

asel

ine

Iron

stat

us in

clus

ion

crite

ria

Cas

e de

tect

ion

and

trea

tmen

t of m

alar

ia

inci

dent

cas

esFi

ndin

gs

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S529Iron metabolism and malaria

partly explain the variations in response to iron supple-mentation reported by different studies other potential complicating factors that contribute to these variations are described in table 4

All but two studies [15 19] have found significant positive effects on markers of iron status in those receiving iron supplementation In the trial of van den Hombergh et al [19] the sample size was limited and baseline characteristics were significantly different between the supplementation and placebo groups Chippaux et al [15] found that anemic children who remained parasite free had increased hemoglobin levels postsupplementation but those that subsequently developed malaria did not The effect of supplementa-tion on hemoglobin concentrations ranged between 06 and 49 gdL with the highest increase occurring in a study that combined iron supplements with anti-malarial therapy [17] Other studies have also shown an additional advantage of iron plus antimalarials as regards hemoglobin recovery [16 18] However despite the hematological benefits all of these studies found nonsignificant increases in adverse malarial outcomes in the groups that received antimalarials plus iron including increased parasite density [16] risk of malaria [18] and treatment failure [17]

Six studies found no effect of iron supplements on malaria risk [19ndash24] of these three included large proportions of anemic subjects (74 to 94) [20 21 24] and one included only children with hemoglobin lt 5 gdL [19] Other studies that stratified by baseline hemoglobin levels [17 25] found that the greatest ben-efits occurred in the most anemic subgroups

Three studies found an increase in clinical malaria attacks in the iron-supplemented groups [10 11 25] and a further six studies found nonsignificant increases in malaria outcomes [14ndash18 26] One of the striking differences between study populations with significant increases in malaria outcomes and those with non-significant effects is access to health care and active treatment of malaria incident cases In fact all but one of the trials [21] that found no effect on malaria outcomes provided access to health care facilities or active follow-up and treatment of malaria incident cases This implies that the potential detrimental effects of iron supplementation may be curtailed by concurrent effective treatment of malaria infections However Verhoef et al and Nwanyanwu et al have shown potential treatment failure effects of combining sulfadoxinendashpyrimethamine with iron in the treatment of preexisting malaria suggesting that antimalarial therapy should precede supplementation [2 17 18]

These observations are further confirmed by a large study in Zanzibar by Sazawal et al [25] that showed increases in malaria-related morbidity and mortality in the iron-supplemented arms of a randomized control-led trial of ironfolate and ironfolate plus zinc versus placebo (summarized in table 2) A subgroup of this Sa

zaw

al[2

5]La

ncet

200

61ndash

35 m

o ir

on (1

25

mg)

+ fo

late

vs

iron

+ fo

late

+ zi

nc v

s pl

aceb

o m

orbi

d-ity

and

mor

talit

y ou

tcom

es a

sses

sed

N

= 3

215

5

43

wer

e pa

rasit

emic

at

bas

elin

eH

b gt

7 g

dL 5

7 o

f ch

ildre

n ha

d H

b lt

10 g

dL

at b

asel

ine

Trea

ted

subs

tudy

chil-

dren

with

clin

ical

m

alar

ia w

ith S

P at

ba

selin

e 6

mo

and

12

mo

Com

bine

d iro

n gr

oups

vs

pla-

cebo

Fo

r adv

erse

mal

aria

-rel

ated

ev

ents

RR

= 1

16

For c

ereb

ral m

alar

ia R

R =

122

Iron

+ fo

late

vs

plac

ebo

For c

ereb

ral m

alar

ia a

s a c

ause

of

dea

th R

R =

17

Subs

tudy

Lo

wer

rate

of a

dver

se e

vent

s in

child

ren

iron

defic

ient

at

base

line

Prot

ectiv

e ef

fect

of i

ron

+ fo

late

in

iron

-def

icie

nt a

nem

ic ch

il-dr

en R

R =

051

Sig

nific

ant d

iffer

ence

s as

repo

rted

by

the

auth

ors

RCT

ran

dom

ized

con

trol

led

tria

l H

b h

emog

lobi

n O

R o

dds

ratio

MC

V m

ean

corp

uscu

lar

volu

me

NS

not

sig

nific

ant

PCV

pac

ked

cell

volu

me

SP

sul

fado

xine

ndashpyr

imet

ham

ine

IPT

inte

rmitt

ent

prev

entiv

e th

erap

y IT

N i

nsec

ticid

e tr

eate

d be

dnet

s ]H

R h

azar

d ra

tio R

R re

lativ

e ris

k

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S530 A M Prentice et al

trial was investigated in more detail and consequently received more intensive diagnosis and treatment of malaria and other infections Substudy children with iron-deficiency anemia at baseline benefited sig-nificantly from iron supplementation in that they had reduced malaria and other infection-related hospital admissions and mortality [25]

The results of this recent study in Zanzibari children have raised new concerns about possible serious side effects of iron supplementation in populations where the etiology of anemia is not solely attributable to iron

deficiency and point to the need for a deeper under-standing of the complex biology of iron sequestration and redistribution between different storage and functional compartments and of the underlying host factors that influence these processes

Effect of malaria on iron metabolism

Erythropoietic iron requirement is met largely through recycling of senescent red blood cells through reticu-loendothelial macrophages where iron is repackaged onto transferrin for transport to the bone marrow [27] Red blood cells are predominantly engulfed directly by reticuloendothelial macrophages however up to 10 of normal recycling occurs as a result of intravascular hemolysis Hemoglobin is released and rapidly bound to haptoglobin and the resultant complex is cleared by liver parenchymal cells or the CD163 macrophagal receptor [28] Malaria-induced destruction of infected and noninfected red blood cells both stresses and impedes the capacity of reticuloendothelial macro-phages to recycle iron back to the bone marrow Intra-vascular rupture of parasitized red cells macrophagal phagocytosis of both parasitized and unparasitized red cells and hypersplenism all contribute to the patho-physiology of the anemia associated particularly with acute malaria

The local epidemiology and transmission character-istics of Plasmodium falciparum together with local drug treatment and intermittent preventive therapy

TABLE 3 Meta-analyses and reviews

First author Sourceyear Study design Findings

Shankar [87] J Infect Dis 2000 Meta-analysis of 13 RCTs of the effect of iron supplementation on malaria and iron status

RR for clinical malaria attack = 11 (NS)RR for slide positive for Plasmodium falci-

parum = 117Absolute increase in infection rate = 57 (NS)RR for spleen enlargement = 112 (NS)Mean increase in Hb = 125 gdLRR for anemia = 05

Oppenheimer [2] J Nutr 2001 Review of controlled interven-tion studies of iron supplemen-tation

Oral iron therapy increased clinical malaria in 5 out of 9 studies

No studies of iron therapy in malarious areas showed benefits on infectious morbidity

Does not report on effect on iron status

Gera [88] BMJ 2002 Systematic review of 28 RCTs of the effect of iron supplementa-tion or fortification in children on infectious illness (including 8 studies of the effect of iron supplementation on malaria)

Pooled OR for malaria-positive smear = 143 but OR when adjusted for baseline malaria smear = 124 (NS)

(The treatment effect increased by 289 times per unit increase in baseline malaria posi-tivity this supports the argument that iron supplementation of children with preexist-ing malaria increases their risk of remaining malaria positive)

Significant differences as reported by the authors RCT randomized controlled trial RR relative risk NS not significant Hb hemoglobin OR odds ratio

TABLE 4 Factors complicating assessment of the relationship between iron status and malaria and the response to iron sup-plementation in malaria-endemic populations

raquo Differences in dose duration and route of iron admin-istration

raquo Degree of malaria immunity in study individuals which can also be related to age and local malaria transmission patterns [7]

raquo Supplementation with iron and folate vs iron alone (especially as some antimalarials have antifolate action) [24]

raquo Markers of iron status used (the confounding effect of infection on serum markers of iron deficiency) [2 8]

raquo Baseline iron status iron-deficient individuals benefit [18 21]

raquo Access to health care and intensity of malaria surveil-lance and treatment during the trial [18 25]

raquo Hemoglobinopathies may affect anemia and response to iron supplementation as well as risk of malaria [9 73]

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S531Iron metabolism and malaria

(IPT) practices influence population immunity and resultant malarial clinical presentation as well as the epidemiology of anemia in a particular setting These factors may also influence the disturbance of iron metabolism and erythropoietic response to iron sup-plementation Acute malaria is associated predomi-nantly with a picture of fever hemolysis and oxidant stress whereas dyserythropoiesis predominates in the anemia of chronic malaria in a semiimmune patient [29] Acute malarial hemolysis represents a major stress on the homeostatic mechanisms of iron flux regulation that have evolved primarily to maintain erythroblast supply while minimizing the oxidant stress-associated effects of iron

Iron can be sequestered and trapped in reticuloen-dothelial macrophages as a result of both chronic and acute malaria and can present a picture of iron-deficient erythropoiesis associated with normal or increased bone marrow iron For instance bone marrow aspirates in 23 Thai patients with uncomplicated acute malaria (age 15 to 52 years) demonstrated malarial pigment in 22 of them Convalescent bone marrow aspirates in 16 patients (3 to 25 days after admission) demonstrated increased iron content compared with the admission sample [30] Five of six Gambian children (lt 5 years of age) with acute malaria had elevated stainable bone marrow iron and four of six children with chronic malaria and severe anemia (hemoglobin lt 6 gdL) had either normal or markedly increased levels of bone marrow stainable iron [31] Eighty-six percent of Indian children and adults (N = 26) with acute and 84 of those with chronic falciparum malaria and anemia (mean hemoglobin 54 gdL N = 38) had normal or increased bone marrow iron stores [32] Ferrokinetic studies involving the intravenous administration of 59Fe demonstrated low unsaturated iron-binding capacity and a rapid plasma iron disappearance time in both parasitemic and postparasitemic patients with acute and secondary (recent acute infection with persistent parasitemia) P falciparum and P vivax in Thai adults compared with controls [33] Incorporation of 59Fe into red blood cells was decreased in acute (N = 5) and secondary parasitemia (11 of 14) but found to be largely normal in the postparasitemic patients includ-ing 3 who were restudied from the parasitemic group Iron sequestration in acute malaria is cytokine driven (elevated tumor necrosis factor α [TNF-α] ILndash1 and interferon γ [IFN-γ] and diminished ILndash10) [29] prob-ably mediated via hepcidin however quantifying this phenomenon assessing how long it persists after acute malaria and in association with chronic malaria and assessing its importance in relation to malarial anemia malaria-associated immunosuppression and response to iron supplementation is difficult since there are few data Conventional indices of iron storage (eg ferritin) or of tissue supply (eg zinc protoporphyrin soluble transferrin receptor transferrin saturation) are

affected by inflammation [8 34ndash36] and the assess-ment of the iron status of young children in malarious areas with acute or chronic malaria is problematic [34] In a holoendemic environment ferritin and eryth-rocyte protoporphyrin were not affected by chronic malaria in older children [37] These indices also do not distinguish between iron deficiency and iron sequestration

Effect of malaria on response to iron supplementation

Malaria-induced anemia does not lead to loss of iron from the body However iron deficiency often coex-ists with malaria in areas of malaria transmission and therapy for severe postmalarial anemia commonly assumes a component due to preexisting iron defi-ciency Iron supplements are routinely prescribed both for severe malaria-associated anemia and for presumed iron-deficient anemia in a malaria-endemic environ-ment Few studies however have looked at the effect of acute malaria on the response to iron supplementation and even fewer have addressed the effect of chronic asymptomatic malaria More commonly studies either have either assessed the response to supplementation of children with anemia of undefined etiology in areas of coexistent malaria iron deficiency and hookworm or have randomized children who were anemic after malaria to a variety of hematinics In a study of 222 Malawian children (lt 5 years of age) with anemia after acute malaria the use of Fansidar and daily supplemen-tal iron resulted in a significantly greater hemoglobin recovery than Fansidar alone or Fansidar and weekly iron only in those children with initial hemoglobin between 5 and 8 gdL [17] However a larger propor-tion of the iron-treated children failed to clear their malaria In the Gambia 600 children (mean age 52 months mean hemoglobin 96 gdL) with uncompli-cated falciparum malaria randomized to receive chlo-roquine or Fansidar as treatment and then either iron folic acid or placebo for 28 days [22] demonstrated a significantly better hemoglobin response with iron than with placebo or folic acid (the difference in mean hemoglobin level after 1 month was 07 gdL) One hundred Tanzanian children (lt 30 months of age) with severe anemia (hemoglobin lt 5 gdL) were randomized either to receive daily iron supplementation or to be controls after antimalarial treatment [19] Among the 60 who completed the 12-week follow-up without a transfusion (30 in each group) there were no differ-ences in hemoglobin recovery From these studies the role of iron supplementation in the treatment of anemia after acute malaria is unclear and it is likely that the hemoglobin response to supplementation is influenced by both the direct inflammatory effect of malaria on iron absorption and utilization and preexistent iron

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S532 A M Prentice et al

deficiency which is impossible to assess in the presence of malaria In the Gambia we recently compared the absorption of stable-isotope-labeled iron in children anemic as a result of iron deficiency and children anemic after acute malaria Both groups were given 30 days of iron supplementation and the malaria group demonstrated significantly better hemoglobin recovery despite initially significantly reduced iron absorption (Doherty et al unpublished results) Utilization of sequestered iron is likely to be a major contributor to erythroblastic iron requirement after acute malaria

Studies of iron supplementation of populations of anemic children in malarious areas have reported either improved hemoglobin response or decreased prevalence of severe anemia [16 22 38 39] Incorpo-ration of antimalarial intervention arms is common Malaria transmission characteristics study design use of antecedent antimalarials differing iron supplemen-tation doses and differing outcome measures as well as different prevalence rates of iron deficiency and hook-worm infection have made the assessment of factors affecting hemoglobin response to iron supplementation difficult In particular the effect of chronic malaria on response to supplementation in high-transmission areas is unclear as the etiology of the anemia and the chronicity of malaria parasitemia are often undefined in study subjects In an area of intense transmission in Tanzania in which more than 80 of children (4 to 71 months old) were parasitemic at baseline and where malaria infection was strongly associated with hemo-globin supplementation improved the iron status and motor and language development of an iron-deficient population but not did not improve hemoglobin [21 36 40] The authors concluded that factors including malarial parasitemia or ineffective erythropoiesis due to inflammatory processes in a population with high levels of infectious morbidity and inflammation might have limited erythropoiesis

An inflammatory-mediated block to iron absorp-tion and utilization is likely to limit the erythropoietic response to supplemental iron after acute malaria how-ever it is unclear whether chronic parasitemia similarly limits the response to supplemental iron The asso-ciation of chronic malaria with anemia [39] stainable bone marrow iron [34] and increased cytokine levels [41] might suggest a probable effect and the eradica-tion of parasites has been associated with hemoglobin improvement without supplemental iron [31]

Iron metabolism by malaria parasites

In this section we consider whether the availability of iron in the host could modulate the efficiency with which malaria parasites can establish an infection and the severity of that infection What evidence is there to support the ldquonutritional immunityrdquo hypothesis that

host iron availability could limit parasite invasion or multiplication andor the clinical sequelae of para-site infection Support for the nutritional immunity hypothesis first stated in the 1970s has generally waned for the majority of pathogens [2] but there may still be a case for obligate intracellular pathogensmdashincluding Plasmodium spp

It may be informative to examine the research of other scientists than those typically involved in the cur-rent debate For example in order for this hypothesis to be truemdashat least in terms of the success of parasite invasion and replicationmdashit is a requirement that P falciparum be dependent on host iron sources for its survival Next is iron deficiency ever likely to be a limiting factor in the supply of iron to the parasite The most recent research suggests that P falciparum does utilize iron from the host but not from the abundant supplies available in erythrocyte hemoglobin the heme portion of which is quickly degraded to nontoxic but non-iron-bioavailable hemozoin or from the plasma via transferrin but from another source possibly an intraerythrocytic labile pool of ferrous iron [42 43] Interestingly measurements of this labile ferrous iron in normal and sickled erythrocytes indicate it to be positively associated with hemoglobin concentrations and negatively associated with plasma ferritin [44] However other researchers have reported evidence to suggest that the degradation of heme to hemozoin is incomplete and that 50 of heme may be degraded via an alternative pathway involving reduced glutathione and releasing bioavailable iron [45 46] As it has been estimated that less than 1 of heme iron would be sufficient to meet parasite iron requirements [47] iron deficiency would never induce iron-limited growth if hemoglobin were the iron source for parasites

Another mechanism by which iron deficiency may limit parasite growth is that proposed recently by Iyer et al [48] who demonstrated the inhibition of hemozoin formation from toxic free heme by the naturally occur-ring zinc protoporphyrin IX (ZPP) at levels likely to be encountered in anemic erythrocytes It is interesting to note that this is thought to be the mechanism by which the quinoline antimalarials act Furthermore Iyer et al demonstrated that quinolines competed for ZPP bind-ing and prevention of hemozoin formation It is pos-sible that via this mechanism moderate anemia could allow the persistence of low levels of parasitemia and therefore affect the development of exposure-related antibody repertoire and clinical immunitymdashwith consequent effects on future malarial incidence and malaria-associated anemia However the evidence for such an effect in human populations is currently limited due to the lack of longitudinal studies assessing ZPP levels and parasite prevalence and density from infancy onwards

Another research area that has been used to support the hypothesis of decreased iron availability is that

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S533Iron metabolism and malaria

of the effects of iron chelators on parasite growth in vitro and in vivo [49 50] Furthermore some antima-larial drugs such as the antibiotic cyclines including doxycycline are also iron chelators However iron chelators may not be acting by depriving the parasite of iron Alternative mechanisms have been suggested for some chelators including the induction of reactive oxygen species from dissociation of iron from heme and hemozoin as suggested for the lipophilic FR160 [51] similar to the suggested mechanism of artemisinin [52] Furthermore differences between the efficacy of chelators in vitro and in vivo have been associated with differences in immune modulation [53] This may suggest that iron status could affect malarial outcomes via direct effects on immune modulation as suggested by Nyakeriga et al [54] The evidence base for the effects of current iron-chelator therapies in reducing the prevalence density or clinical sequelae of malaria is weakmdashas outlined in a recent Cochrane review of clinical trials involving the use of either desferioxamine or the orally available deferiprone [55] in which all of the seven studies included had limitations relat-ing to study size relevance of study populations and more critically methodological and analytical faults However the authors of this review concluded that the results suggested possible benefits of treatment in cerebral malaria with a shorter recovery time from coma and decreased time to parasite clearance The initial justification for using iron-chelator therapy in cerebral malaria was based on the premise of prevent-ing iron-induced damage to brain cells resulting from hemolysis Therefore it is important to note that the possible benefits of iron-chelator therapy may not relate to limitation of iron for parasite growth and may there-fore not provide evidence in support of the nutritional immunity hypothesis

Iron malaria and hemoglobinopathies

How do hemoglobinopathies protect against parasite invasion or multiplication andor clinical sequelae of parasite infection Are these polymorphisms likely to affect the relationship between iron status or supple-mentation and malaria

J B S Haldane is credited with first postulat-ing heterozygote selection as an explanation for the high prevalence of the thalassemias and later other hemoglobinopathies He suggested that the small size reduced hemoglobin concentrations and increased resistance to hypertonic solutions of such cells may result in decreased parasite invasion or growth Although this hypothesis has been widely accepted for some time it has only recently been possible to dem-onstrate that these mutations have been maintained by selection mostly by malaria but possibly also other infectious causes However the extent and mechanisms

of protection are still debated At least in vitro many studies have failed to demonstrate decreased ability of parasites to invade or grow in thalassemic cells or cells containing hemoglobin S (HbS) Instead the mecha-nisms appear to be more complicated and possibly to vary between local conditions

The common polymorphisms involved in hemo-globin synthesis or red cell formation include sickle hemoglobin (HbS) HbC and HbE the α and β-thalassemias and South Asian ovalocytosis The geographic distribution of these varies across tropi-cal areas and can vary extensively even within closely related regions Current estimates of these polymor-phisms are often based on single sites and are likely to be underestimates [56] but a figure of 27 million carriers of the main hemoglobinopathies has been proposed [56] The carrier frequency for HbS is esti-mated at between 5 and 40 in populations across sub-Saharan Africa the Middle East and parts of South Asia HbC is limited to parts of West and North Africa whereas HbE is common in some parts of India and Southeast Asia with carrier rates up to 60 The thalassemias have the broadest geographic distribution and also the widest range of causative mutations and clinical outcomes The carrier frequencies for the more severe range of β-thalassemias is generally lower than for the α-thalassemias which are estimated to reach carrier frequencies of up to 20 in sub-Saharan Africa higher in Middle Eastern and Indian populations and up to 80 in some Pacific populations (reviewed in Williams et al [57] Rees et al [58] and Maitland et al [59])

In β-thalassemias excess α-globin chains precipitate in red cell precursors leading to ineffective erythropoi-esis and resulting in anemia in the context of increased iron absorption and iron accumulation The clinical expression of β-thalassemia varies widely depending on the exact genetic lesions inherited and interactions with other genetic loci including the α and γ globin genes β-Thalassemia trait and β-thalassemia interme-diate are often asymptomatic and may not be diagnosed except for mild anemia In α-thalassemia the excess β-chains form stable homotetramers which do not sig-nificantly affect erythropoiesis but cause an increased rate of hemolysis of mature cells The degree of the deficit of α-globin chains depends on the number of α-globin genes inactivated and unless three α-globin genes are lost the effects are subtle and various so that the condition will go largely undiagnosed It might be supposed that iron supplementation could be more deleterious in populations with a high prevalence of β-thalassemia mutations because of the inability to utilize the iron leading to increased iron availability to pathogens or iron-induced oxidant stress Interest-ingly Oppenheimer [2] reported that the increased susceptibility to malaria associated with parenteral iron in Papua New Guinean children was not apparent in

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S534 A M Prentice et al

single-deletion α-thalassemia compared with normal children

In a prospective casendashcontrol study in Papua New Guinea α-thalassemic α+ndash homozygotes and α+ndash heterozygotes had a greatly decreased risk of severe malaria (incidence rate ratio = 04 and 066) compared with controls [9] Furthermore protection was also observed for hospitalization from other infections possibly suggesting an immune component to the pro-tection [60] although the reduction of severe malaria may reduce infectious sequelae by invasive bacte-rial disease In apparent contrast α-thalassemia has also been associated with an increased prevalence of uncomplicated malaria in Vanuatu particularly in very young children with P vivax [57] It was suggested that increased red cell turnover in these children increased susceptibility to P vivax [58] resulting in cross-species immunity to P falciparum in later life [59] A similar finding was reported for glucose-6-phosphate dehy-drogenase (G6PD) deficiency in a cohort study in Uganda in which many other potential risk factors for malarial infection were controlled for (age water source use of prophylaxis bednet usage and proxim-ity to mosquito breeding sites) Female heterozygotes for G6PD had a significantly increased incidence of uncomplicated malaria (IRR = 13 p = 03) and a trend for increased parasite densities similar trends were seen for hemizygote males This was different from the pattern observed for HbS heterozygotes who had a nonsignificantly decreased incidence of uncomplicated malaria and decreased parasite densities [61]

A mechanism that has been suggested for G6PD defi-ciency and that may also be applicable to sickle (HbAS) and thalassemic cells involves decreased oxidative protection (G6PD) or increased constitutive oxidative stress of these cells (HbAS αβ thalassemias) especially when infected resulting in increased clearance of the cells from non-malaria-specific immune mechanisms essentially the same as the normal removal of old ldquosenescentrdquo red cells by phagocytes [62ndash64] It has been proposed that such a mechanism could prevent parasitemias from reaching critically high densities and therefore protect from severe malaria and also facilitate the development of antibody repertoires in children from the maintenance of low-grade infections in young children [65ndash67] In a slight modification of this hypothesis the increased phagocytic removal of early ring-stage infected cellsmdashcompared with schizonts and trophozoitesmdashhas been demonstrated for G6PD β-thalassemic and HbAS cells in vitro but not for α-thalassemic infected cells [68] The phagocytosis of ring compared with later stages may be advantageous since rings contain less hemozoin the buildup of which in monocytes has been associated with decreased func-tion Additionally the reduction of the later stages of parasite development may reduce the development of severe symptoms such as cerebral malaria from

reduced endothelial adhesion of late-stage infected red blood cells to receptors such as intracellular adhesion molecule-1 (ICAM-1)

The epidemiological evidence for a protective effect of HbAS suggests that the protective effects are great-est for severe disease (reviewed by Roberts et al [69]) In the most comprehensive study to date a detailed prospective cohort in two Kenyan populations it was reported that HbS heterozygotes had a significantly decreased risk of mild clinical malaria as assessed by active surveillance (50 decreased risk 95 confi-dence interval [CI] 26 to 67]) a 75 (95 CI 84 to 61) decreased risk of hospital admission for malaria and a 90 [95 CI 3 to 99] decreased risk of severe malaria (severe malarial anemia cerebral malaria or complicated malaria) [70] There was no effect of HbAS on the risk of asymptomatic infec-tions or of parasite density in asymptomatic infections assessed at four cross-sectional surveys There were significant decreases in parasite densities for all of the other categories of infection Additionally in this study unlike another in western Kenya [71] the protection was specific to malaria and did not extend to other common childhood infections including respiratory infections gastroenteritis and helminth infections

What influence the hemoglobinopathic and other polymorphisms may have on the effect of iron sup-plementation on malarial susceptibility is potentially dependent on the extent and mechanisms of protection from infection in the different genotypesmdashinfluences that are likely to be further complicated by differential effects according to age and malarial exposure and effects of coinheritance [72] The coinheritance of the HbS G6PD deficiency and α-thalassemia deletion alle-les is likely to be prevalent in sub-Saharan populations making the study of such effects in real populations extremely difficult by requiring very large sample sizes and complex statistical modeling

To the authorsrsquo knowledge only two published randomized controlled trials of iron supplementation have assessed the effects by genotypemdashin both cases by HbAS versus HbAA [73 74]

In the first trial involving Traditional Birth Attend-ant-administered routine iron supplementation to multigravid Gambian pregnant women Menendez et al [73] reported that although overall there were significant beneficial effects on hemoglobin and packed cell volume (PCV) and on birthweight these effects were entirely accounted for by women with the HbAA phenotype (N = 402 vs N = 98) whereas iron-supplemented HbAS women had lower HB PCV and birthweight than HbAA women receiving placebo Furthermore even in this relatively small study these interactions were statistically significant (p lt 01 for hematological indices at delivery baseline measurements as a covariate p lt 03 for birthweight maternal height included as a covariate) Overall

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S535Iron metabolism and malaria

there was no reported increase in susceptibility to malaria as assessed by the prevalence of peripheral malaria at late pregnancy and delivery or by placental histology Yet iron-supplemented HbAS women had an increased prevalence of placental malaria (76 [2229]) compared with iron-supplemented HbAA women (53 [83158]) placebo-treated HbAA women (59 [91154]) or placebo-treated HbAS women (58 [1933]) At the time of this study IPT prophylaxis was recommended only for primigravid pregnant women in the Gambia hence the choice of the study population What the effects of iron supplementation might be in either primigravidae or multigravidae receiving IPTmdashwhich is now recommended for all pregnant women in malaria-endemic countriesmdashhas not been assessed The protection afforded by the HbAS genotype is likely to vary according to gravidity and malarial endemic-ity In areas of high transmission the majority of the increased risk is borne by primigravidae whereas in areas of lower and highly defined seasonal transmis-sion the increased risk extends to a greater number of pregnancies [75] The protective effect of HbAS is thought to be greatest in relatively nonimmune young children who have not yet developed acquired immunity by exposure to a variety of clonal variants of P falciparum and therefore have not developed a full antibody repertoire to the variant surface antigens (VSA) expressed on the cell surfaces of parasitized red blood cells

In the second trial the effect of the HbAS phenotype on the response to iron supplementation in children was assessed in a subanalysis of a 2 times 2 randomized controlled trial of iron supplementation and inter-mittent preventive treatment (IPT) for malaria using sulfadoxinendashpyrimethamine in anemic Kenyan chil-dren (hemoglobin 7 to 109 gdL) [74] There was no reported increase in the susceptibility to clinical malaria or the prevalence of parasitemia at monthly screening associated with the iron supplementation alone or with IPT [16] whereas IPT plus iron was the most effective in increasing hemoglobin concentrations There were no significant statistical interactions between HbASAA phenotypes and treatment group However there was a nonsignificant increase in the incidence rate ratio of clinical malaria in the HbAS group not receiv-ing IPT during the 12 weeks of follow-up (IRR = 416 95 CI 05 to 346) and increased geometric mean parasite density in both groups but by far the biggest difference was seen in the group receiving IPT (6203 vs 1853 p = 08 for the interaction) The authors acknowledge that the number of clinical events was very small and that these findings would need veri-fication in a larger study since the number of HbAS individuals (approximately 25 to 30) in each treatment group versus approximately 100 HbAA individuals plus the short follow-up time means that the study was grossly underpowered to assess these outcomes If this

effect is real then the age group studied in this trial (2 to 36 months with 78 lt 18 months) should include the most affected although greater effects might be observed in areas of lower transmission and therefore also in a greater age range of children The results of these two trials warrant urgent further trials or retro-spective analysis of prior trials with sufficient power and detail to make firm conclusions on the effects of common polymorphisms on the response to iron sup-plementation which may be expected to vary by age group and transmission intensity

Clinical trials of IPT during infancy (IPTi) have demonstrated a reduction in the prevalence of anemia in young children in malaria-endemic areas [16 18 38 76] and in some trials a reduction in the incidence of clinical malaria [38 76] and morbidity and mortality in the first year of life [38 77] However the effects may vary depending on the timing of dosing choice of drug local levels of resistance and levels of transmission [78 79] On the basis of our analysis above the impact of IPTi plus iron supplementation may be modulated by levels of hemoglobinopathies and therefore suba-nalyses of these studies should be performed according to genotype wherever possible

Interactions of polymorphisms in host iron metabolism and regulatory proteins with malaria

Polymorphisms of haptoglobin a plasma protein that binds free hemoglobin released from lysed red blood cells recirculating the heme portion to the bone marrow through monocyte and macrophage uptake via CD136 have also been associated with malarial outcomes although reports are conflicting Hap-toglobin exists as three common phenotypes Hp1-1 1-2 and 2-2 In case-control studies in India Sudan Ghana and Cameroon the Hp2-2 phenotype has been associated with protection from severe malaria and placental infection [80ndash83] However two studies that have assessed associations with haptoglobin genotypes did not report any associations [84 85] In a cohort study in Gambian children the Hp2-2 genotype was associated with a greater drop in hemoglobin concen-trations across a malarial transmission season [65] The authors proposed that this effect may have been mediated through an increased prevalence of asymp-tomatic infection observed in the Hp2-2 group which contributed to anemia but could provide protection against severe malaria Interestingly similar but smaller drops in hemoglobin concentration were also observed for heterozygotes for G6PD and HbS We are currently analyzing the effects of low-dose iron supplementation during a malarial transmission season in a similar cohort of children

Inducible heme oxygenase (iHO-1) catalyzes the

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S536 A M Prentice et al

breakdown of heme to generate iron carbon monoxide and biliverdin and is expressed in monocytes and mac-rophages among other cells Biliverdin is subsequently degraded to bilirubin which has potent antioxidant effects Microsatellite polymorphisms in the number of tandem repeats in the promoter of iHO-1 have been variously associated with increased and decreased oxidant stress in various disease pathologies However in a case-control study of cerebral malaria patients in Myanmar homozygotes for the short number of repeats (lt 28) previously associated with higher levels of transcription of iHO-1 were significantly more likely to have cerebral malaria than uncomplicated malaria (odds ratio 314 p = 008) [86] It is not clear how this effect may be mediated but it is possible that it results from increased levels of free iron and resulting oxidant stress

In summary the mechanisms by which various genetic polymorphisms interact with malarial infec-tion are still not clear Furthermore it is not clear how they may affect a possible relationship between iron and malaria especially in relation to supplementation which should be differentiated from that of iron status The current evidence suggests that the heterozygous states of the hemoglobinopathies do not protect against malaria by a simple mechanism involving iron with-holding from the pathogen However the effects of iron supplementation in individuals with the most common polymorphisms should be carefully evaluated taking into account differences in transmission intensity and iron status at baseline

Conclusions

The evidence reviewed above tends to substantiate the concerns raised by the recent Pemba trial that universal administration of iron to children in malarious areas may be associated with adverse outcomes The mecha-nism by which this occurs is far from clear and merits

further research to test whether other chemical forms of supplementary iron might carry less risk There is also evidence that the risk profile will be altered by host genetic variations in hemoglobinopathies G6PD and genes regulating iron metabolism However these insights are not of great practical value because population screening and targeted supplementation programs are not feasible in the areas where iron defi-ciency is most prevalent Likewise the evidence that anemic children are probably at low risk for any adverse outcomes associated with iron supplementation implies a need for prescreening that may not be cost-effective or logistically feasible in developing-country settings

The evidence is fairly clear that malaria causes anemia by diverting iron away from bone marrow and erythropoiesis as part of the inflammatory response and hence iron administration alone is not likely to be the most effective means of combating the anemia Other therapeutic paradigms that combat the inflam-mation and adjust the timing of iron administra-tion to children recovering from malaria should be researched

We suggest that further research is still required to confirm the apparent relationships between iron status and malaria and that such studies should also focus on the underlying mechanisms of the putative interaction This might be achieved through the establishment of a multicountry collaboration to standardize protocols both for iron-supplementation interventions and for the assessment of iron and malaria status indicators Standardizing protocols across variations in age groups malaria transmission patterns and genetic distribu-tions of hemoglobinopathies will provide the evidence for a more targeted approach to policies of prevention and treatment of anemia in malaria-endemic regions

Until this evidence is gathered we recommend that iron supplementation in malarious areas must be accompanied by effective systems for ensuring univer-sal rapid access to diagnosis and treatment of malaria or by preventive therapy

References

1 WHO UNICEF Focusing on anaemia Towards an integrated approach for effective anaemia control Joint WHO UNICEF Statement Geneva Joint WHO UNICEF Statement 2004

2 Oppenheimer SJ Iron and its relation to immunity and infectious disease J Nutr 2001131616Sndash33S discussion 33Sndash35S

3 Murray MJ Murray AB Murray NJ Murray MB Diet and cerebral malaria the effect of famine and refeeding Am J Clin Nutr 19783157ndash61

4 Nyakeriga AM Troye-Blomberg M Dorfman JR Alexander ND Back R Kortok M Chemtai AK Marsh K Williams TN Iron deficiency and malaria among children living on the coast of Kenya J Infect Dis 2004 190439ndash47

5 Oppenheimer SJ Macfarlane SB Moody JB Bunari O Hendrickse RG Effect of iron prophylaxis on morbidity due to infectious disease report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 1986 80596ndash602

6 Shipton D Association between haemoglobin level and susceptibility to malaria a study of Gambian children [MSc dissertation] London London School of Hygiene and Tropical Medicine 2004

7 Snow RW Byass P Shenton FC Greenwood BM The relationship between anthropometric measurements and measurements of iron status and susceptibility to malaria in Gambian children Trans R Soc Trop Med Hyg 199185584ndash9

8 Asobayire FS Adou P Davidsson L Cook JD Hurrell

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S537Iron metabolism and malaria

RF Prevalence of iron deficiency with and without concurrent anemia in population groups with high prevalences of malaria and other infections a study in Cote drsquoIvoire Am J Clin Nutr 200174776ndash82

9 Allen SJ OrsquoDonnell A Alexander ND Alpers MP Peto TE Clegg JB Weatherall DJ alpha+-Thalassemia protects children against disease caused by other infec-tions as well as malaria Proc Natl Acad Sci U S A 1997 9414736ndash41

10 Murray MJ Murray AB Murray MB Murray CJ The adverse effect of iron repletion on the course of certain infections Br Med J 197821113ndash5

11 Smith AW Hendrickse RG Harrison C Hayes RJ Greenwood BM The effects on malaria of treatment of iron-deficiency anaemia with oral iron in Gambian children Ann Trop Paediatr 1989917ndash23

12 Oppenheimer SJ Gibson FD Macfarlane SB Moody JB Harrison C Spencer A Bunari O Iron supplementation increases prevalence and effects of malaria report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 198680603ndash12

13 Byles AB Drsquosa A Reduction of reaction due to iron dextran infusion using chloroquine Br Med J 19703625ndash7

14 Berger J Dyck JL Galan P Aplogan A Schneider D Traissac P Hercberg S Effect of daily iron supplementa-tion on iron status cell-mediated immunity and inci-dence of infections in 6ndash36 month old Togolese children Eur J Clin Nutr 20005429ndash35

15 Chippaux JP Schneider D Aplogan A Dyck JL Berger J [Effects of iron supplementation on malaria infection] Bull Soc Pathol Exot 19918454ndash62

16 Desai MR Mei JV Kariuki SK Wannemuehler KA Phil-lips-Howard PA Nahlen BL Kager PA Vulule JM ter Kuile FO Randomized controlled trial of daily iron sup-plementation and intermittent sulfadoxine-pyrimeth-amine for the treatment of mild childhood anemia in western Kenya J Infect Dis 2003187658ndash66

17 Nwanyanwu OC Ziba C Kazembe PN Gamadzi G Gandwe J Redd SC The effect of oral iron therapy during treatment for Plasmodium falciparum malaria with sulphadoxine-pyrimethamine on Malawian chil-dren under 5 years of age Ann Trop Med Parasitol 199690589ndash95

18 Verhoef H West CE Nzyuko SM de Vogel S van der Valk R Wanga MA Kuijsten A Veenemans J Kok FJ Intermittent administration of iron and sulfadoxine-py-rimethamine to control anaemia in Kenyan children a randomised controlled trial Lancet 2002360908ndash14

19 van den Hombergh J Dalderop E Smit Y Does iron therapy benefit children with severe malaria-associated anaemia A clinical trial with 12 weeks supplementation of oral iron in young children from the Turiani Division Tanzania J Trop Pediatr 199642220ndash7

20 Lawless JW Latham MC Stephenson LS Kinoti SN Pertet AM Iron supplementation improves appetite and growth in anemic Kenyan primary school children J Nutr 1994124645ndash54

21 Mebrahtu T Stoltzfus RJ Chwaya HM Jape JK Savioli L Montresor A Albonico M Tielsch JM Low-dose daily iron supplementation for 12 months does not increase the prevalence of malarial infection or den-sity of parasites in young Zanzibari children J Nutr 20041343037ndash41

22 Menendez C Kahigwa E Hirt R Vounatsou P Aponte JJ Font F Acosta CJ Schellenberg DM Galindo CM Kimario J Urassa H Brabin B Smith TA Kitua AY Tanner M Alonso PL Randomised placebo-controlled trial of iron supplementation and malaria chemoproph-ylaxis for prevention of severe anaemia and malaria in Tanzanian infants Lancet 1997350844ndash50

23 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S MrsquoBoge B Greenwood BM The effects of iron supplementation during pregnancy given by traditional birth attendants on the prevalence of anaemia and malaria Trans R Soc Trop Med Hyg 199488590ndash3

24 van Hensbroek MB Morris-Jones S Meisner S Jaffar S Bayo L Dackour R Phillips C Greenwood BM Iron but not folic acid combined with effective antimalarial therapy promotes haematological recovery in African children after acute falciparum malaria Trans R Soc Trop Med Hyg 199589672ndash6

25 Sazawal S Black RE Ramsan M Chwaya HM Stoltzfus RJ Dutta A Dhingra U Kabole I Deb S Othman MK Kabole FM Effects of routine prophylactic supplemen-tation with iron and folic acid on admission to hospital and mortality in preschool children in a high malaria transmission setting community-based randomised placebo-controlled trial Lancet 2006367133ndash43

26 Harvey PW Heywood PF Nesheim MC Galme K Zegans M Habicht JP Stephenson LS Radimer KL Brabin B Forsyth K et al The effect of iron therapy on malarial infection in Papua New Guinean schoolchil-dren Am J Trop Med Hyg 19894012ndash8

27 Andrews NC Iron homeostasis insights from genetics and animal models Nat Rev Genet 20001208ndash17

28 Kristiansen M Graversen JH Jacobsen C Sonne O Hoffman HJ Law SK Moestrup SK Identification of the haemoglobin scavenger receptor Nature 2001409 198ndash201

29 Wickramasinghe SN Abdalla SH Blood and bone marrow changes in malaria Baillieres Best Pract Res Clin Haematol 200013277ndash99

30 Phillips RE Looareesuwan S Warrell DA Lee SH Karbwang J Warrell MJ White NJ Swasdichai C Weatherall DJ The importance of anaemia in cerebral and uncomplicated falciparum malaria role of compli-cations dyserythropoiesis and iron sequestration Q J Med 198658305ndash23

31 Abdalla S Weatherall DJ Wickramasinghe SN Hughes M The anaemia of P falciparum malaria Br J Haematol 198046171ndash83

32 Sen R Bhatnagar BM Singh U Yadav MS Sehgal PK Patterns of erythropoiesis and anaemia in malaria J Commun Dis 199022247ndash53

33 Srichaikul T Wasanasomsithi M Poshyachinda V Panikbutr N Rabieb T Ferrokinetic studies and eryth-ropoiesis in malaria Arch Intern Med 1969124623ndash8

34 Das BS Thurnham DI Das DB Influence of malaria on markers of iron status in children implications for interpreting iron status in malaria-endemic communi-ties Br J Nutr 199778751ndash60

35 Menendez C Quinto LL Kahigwa E Alvarez L Fern-andez R Gimenez N Schellenberg D Aponte JJ Tanner M Alonso PL Effect of malaria on soluble transferrin receptor levels in Tanzanian infants Am J Trop Med Hyg 200165138ndash42

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S538 A M Prentice et al

36 Stoltzfus RJ Chwaya HM Montresor A Albonico M Savioli L Tielsch JM Malaria hookworms and recent fever are related to anemia and iron status indicators in 0- to 5-y old Zanzibari children and these relationships change with age J Nutr 20001301724ndash33

37 Stoltzfus RJ Chwaya HM Albonico M Schulze KJ Savioli L Tielsch JM Serum ferritin erythrocyte pro-toporphyrin and hemoglobin are valid indicators of iron status of school children in a malaria-holoendemic population J Nutr 1997127293ndash8

38 Massaga JJ Kitua AY Lemnge MM Akida JA Malle LN Ronn AM Theander TG Bygbjerg IC Effect of intermittent treatment with amodiaquine on anaemia and malarial fevers in infants in Tanzania a randomised placebo-controlled trial Lancet 20033611853ndash60

39 Verhoef H West CE Kraaijenhagen R Nzyuko SM King R Mbandi MM van Laatum S Hogervorst R Schep C Kok FJ Malarial anemia leads to adequately increased erythropoiesis in asymptomatic Kenyan children Blood 20021003489ndash94

40 Stoltzfus RJ Chway HM Montresor A Tielsch JM Jape JK Albonico M Savioli L Low dose daily iron supplementation improves iron status and appetite but not anemia whereas quarterly anthelminthic treatment improves growth appetite and anemia in Zanzibari preschool children J Nutr 2004134348ndash56

41 Kurtzhals JA Addae MM Akanmori BD Dunyo S Koram KA Appawu MA Nkrumah FK Hviid L Anae-mia caused by asymptomatic Plasmodium falciparum infection in semi-immune African schoolchildren Trans R Soc Trop Med Hyg 199993623ndash7

42 Loyevsky M John C Dickens B Hu V Miller JH Gordeuk VR Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators Mol Biochem Parasitol 199910143ndash59

43 Scholl PF Tripathi AK Sullivan DJ Bioavailable iron and heme metabolism in Plasmodium falciparum Curr Top Microbiol Immunol 2005295293ndash324

44 Darbari D Loyevsky M Gordeuk V Kark JA Castro O Rana S Apprey V Kurantsin-Mills J Fluorescence meas-urements of the labile iron pool of sickle erythrocytes Blood 2003102357ndash64

45 Ginsburg H Iron acquisition by Plasmodium spp Para-sitol Today 199915466

46 Atamna H Ginsburg H Heme degradation in the presence of glutathione A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells J Biol Chem 199527024876ndash83

47 Gabay T Ginsburg H Hemoglobin denaturation and iron release in acidified red blood cell lysatemdasha possible source of iron for intraerythrocytic malaria parasites Exp Parasitol 199377261ndash72

48 Iyer JK Shi L Shankar AH Sullivan DJ Jr Zinc pro-toporphyrin IX binds heme crystals to inhibit the proc-ess of crystallization in Plasmodium falciparum Mol Med 20039175ndash82

49 Cabantchik ZI Moody-Haupt S Gordeuk VR Iron che-lators as anti-infectives malaria as a paradigm FEMS Immunol Med Microbiol 199926289ndash98

50 Hershko C Control of disease by selective iron deple-tion a novel therapeutic strategy utilizing iron chelators Baillieres Clin Haematol 19947965ndash1000

51 Pradines B Tall A Ramiandrasoa F Spiegel A Sokhna C Fusai T Mosnier J Daries W Trape JF Kunesch G Parzy D Rogier C In vitro activity of iron-binding compounds against Senegalese isolates of Plasmodium falciparum J Antimicrob Chemother 2006571093ndash9

52 Meshnick SR Yang YZ Lima V Kuypers F Kam-chonwongpaisan S Yuthavong Y Iron-dependent free radical generation from the antimalarial agent artem-isinin (qinghaosu) Antimicrob Agents Chemother 1993371108ndash14

53 Golenser J Domb A Mordechai-Daniel T Leshem B Luty A Kremsner P Iron chelators correlation between effects on Plasmodium spp and immune functions J Parasitol 200692170ndash7

54 Nyakeriga AM Williams TN Marsh K Wambua S Perlmann H Perlmann P Grandien A Troye-Blomberg M Cytokine mRNA expression and iron status in chil-dren living in a malaria endemic area Scand J Immunol 200561370ndash5

55 Smith HJ Meremikwu M Iron chelating agents for treating malaria Cochrane Database Syst Rev 2003CD001474

56 Weatherall DJ The global problem of genetic disease Ann Hum Biol 200532117ndash22

57 Williams TN Maitland K Bennett S Ganczakowski M Peto TE Newbold CI Bowden DK Weatherall DJ Clegg JB High incidence of malaria in alpha-thalassaemic children Nature 1996383522ndash5

58 Rees DC Williams TN Maitland K Clegg JB Weather-all DJ Alpha thalassaemia is associated with increased soluble transferrin receptor levels Br J Haematol 1998103365ndash9

59 Maitland K Williams TN Bennett S Newbold CI Peto TE Viji J Timothy R Clegg JB Weatherall DJ Bowden DK The interaction between Plasmodium falciparum and P vivax in children on Espiritu Santo island Van-uatu Trans R Soc Trop Med Hyg 199690614ndash20

60 Weatherall DJ Clegg JB Genetic variability in response to infection malaria and after Genes Immun 2002 3331ndash7

61 Parikh S Dorsey G Rosenthal PJ Host polymorphisms and the incidence of malaria in Ugandan children Am J Trop Med Hyg 200471750ndash3

62 Destro Bisol G Genetic resistance to malaria oxidative stress and hemoglobin oxidation Parassitologia 1999 41203ndash4

63 Cappadoro M Giribaldi G OrsquoBrien E Turrini F Mannu F Ulliers D Simula G Luzzatto L Arese P Early phago-cytosis of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes parasitized by Plasmodium falciparum may explain malaria protection in G6PD deficiency Blood 1998922527ndash34

64 Arese P Turrini F Schwarzer E Band 3complement-mediated recognition and removal of normally senes-cent and pathological human erythrocytes Cell Physiol Biochem 200516133ndash46

65 Atkinson SH Rockett K Sirugo G Bejon PA Fulford A OrsquoConnell M A Bailey R Kwiatkowski DP Prentice AM Seasonal Childhood Anaemia in West Africa Is Associated with the Haptoglobin 2-2 Genotype PLoS Med 20063e172

66 Cabrera G Cot M Migot-Nabias F Kremsner PG Deloron P Luty AJ The sickle cell trait is associated

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S539Iron metabolism and malaria

with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens J Infect Dis 20051911631ndash8

67 Williams TN Mwangi TW Roberts DJ Alexander ND Weatherall DJ Wambua S Kortok M Snow RW Marsh K An immune basis for malaria protection by the sickle cell trait PLoS Med 20052e128

68 Ayi K Turrini F Piga A Arese P Enhanced phagocyto-sis of ring-parasitized mutant erythrocytes a common mechanism that may explain protection against falci-parum malaria in sickle trait and beta-thalassemia trait Blood 20041043364ndash71

69 Roberts DJ Harris T Williams T The influence of inherited traits on malaria infection In Bellamy R ed Susceptibility to infectious diseases the importance of host genetics Cambridge Cambridge University Press 2004 139ndash84

70 Williams TN Mwangi TW Wambua S Alexander ND Kortok M Snow RW Marsh K Sickle cell trait and the risk of Plasmodium falciparum malaria and other child-hood diseases J Infect Dis 2005192178ndash86

71 Aidoo M Terlouw DJ Kolczak MS McElroy PD ter Kuile FO Kariuki S Nahlen BL Lal AA Udhayakumar V Protective effects of the sickle cell gene against malaria morbidity and mortality Lancet 20023591311ndash2

72 Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K Nega-tive epistasis between the malaria-protective effects of alpha+-thalassemia and the sickle cell trait Nat Genet 2005371253ndash7

73 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S Ascaso C Smith T MrsquoBoge B Greenwood BM The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS Trans R Soc Trop Med Hyg 199589289ndash92

74 Terlouw DJ Desai MR Wannemuehler KA Kariuki SK Pfeiffer CM Kager PA Shi YP Ter Kuile FO Relation between the response to iron supplementation and sickle cell hemoglobin phenotype in preschool children in western Kenya Am J Clin Nutr 200479466ndash72

75 Duffy PE Fried M Malaria in the pregnant woman Curr Top Microbiol Immunol 2005295169ndash200

76 Schellenberg D Menendez C Kahigwa E Aponte J Vidal J Tanner M Mshinda H Alonso P Intermittent treatment for malaria and anaemia control at time of routine vaccinations in Tanzanian infants a randomised placebo-controlled trial Lancet 20013571471ndash7

77 Schellenberg D Menendez C Aponte JJ Kahigwa E Tanner M Mshinda H Alonso P Intermittent preventive antimalarial treatment for Tanzanian infants follow-up to age 2 years of a randomised placebo-controlled trial Lancet 20053651481ndash3

78 OrsquoMeara WP Breman JG McKenzie FE The promise and potential challenges of intermittent preventive treat-ment for malaria in infants (IPTi) Malar J 2005433

79 White NJ Intermittent presumptive treatment for malaria PLoS Med 20052e3

80 Elagib AA Kider AO Akerstrom B Elbashir MI Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan Trans R Soc Trop Med Hyg 199892309ndash11

81 Minang JT Gyan BA Anchang JK Troye-Blomberg M Perlmann H Achidi EA Haptoglobin phenotypes and malaria infection in pregnant women at delivery in western Cameroon Acta Trop 200490107ndash14

82 Quaye IK Ekuban FA Goka BQ Adabayeri V Kurtzhals JA Gyan B Ankrah NA Hviid L Akanmori BD Hap-toglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria Trans R Soc Trop Med Hyg 200094216ndash9

83 Singh IP Walter H Bhasin MK Bhardwaj V Sudhakar K Genetic markers and malaria Observations in Gujarat India Hum Hered 19863631ndash6

84 Aucan C Walley AJ Greenwood BM Hill AV Hap-toglobin genotypes are not associated with resistance to severe malaria in The Gambia Trans R Soc Trop Med Hyg 200296327ndash8

85 Bienzle U Eggelte TA Adjei LA Dietz E Ehrhardt S Cramer JP Otchwemah RN Mockenhaupt FP Limited influence of haptoglobin genotypes on severe malaria in Ghanaian children Trop Med Int Health 200510668ndash71

86 Takeda M Kikuchi M Ubalee R Na-Bangchang K Ruangweerayut R Shibahara S Imai S Hirayama K Microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with susceptibility to cerebral malaria in Myanmar Jpn J Infect Dis 2005 58268ndash71

87 Shankar AH Nutritional modulation of malaria mor-bidity and mortality J Infect Dis 2000182 Suppl 1 S37ndash53

88 Gera T Sachdev HP Effect of iron supplementation on incidence of infectious illness in children systematic review Bmj 20023251142

Page 2: Iron metabolism and malaria

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S525Iron metabolism and malaria

affect the ironndashmalaria interaction

Observational studies linking iron status and malaria

Early observations in famine environments described the suppression of malaria in severely malnourished populations and its recrudescence in those that sub-sequently consumed iron-rich diets as compared with iron-deficient diets [3] Observational studies that fol-lowed on the effect of iron status on susceptibility to malaria in moderately malnourished populations are summarized in table 1

These studies present a conflicting picture in which raised iron status was associated with increased [4 5] decreased [6] and neutral [7] effects on the subsequent risk of malaria Two studies point toward an increased susceptibility in individuals with high iron stores as measured by serum ferritin levels [4 7] but serum fer-ritin is affected by the acute phase response and is sig-nificantly correlated with markers of inflammation [8] thus making such associations particularly vulnerable to confounding Inconsistencies between study results

may also derive from differences in proportions of indi-viduals with hemoglobinopathies which can confound the relationship between iron status and malaria [9]

Iron supplementation and the risk of malaria

Iron supplementation has been the most widely used approach in the public health attempts to prevent and treat anemia Early studies of the effect of oral iron supplementation on the risk of malaria often found increases in adverse malarial outcomes in supple-mented groups [10 11] as have studies of intramuscu-lar [12] and parenteral [13] iron administration More recent studies however largely report nonsignificant effects of iron supplementation on malaria outcomes [14ndash18] (table 2) Three meta-analyses have also been conducted and are listed in table 3

The trials of iron supplementation in malaria-endemic areas are heterogeneous in dose duration and timing of supplementation age group studied hematological and malariometric inclusion criteria and outcomes assessed These design differences may

TABLE 1 Observational studies

First author Source and year Study design Findings

Oppenheimer[12]

Trans R Soc Trop Med Hyg 1986

Birthndash12 mo subanalysis of placebo group of a trial of intramuscular iron dextran Papua New Guinea N = 212

Infants with Hb gt 137 gdL and Hb gt 157 gdL at birth were 2ndash3 times more likely to have a malaria-positive slide at 12 mo

(This population has high rates of single-deletion α-thalassemia which causes anemia and protects against malaria and is therefore a potential confounder)

Snow[7]

Trans R Soc Trop Med Hyg 1991

1ndash8 yr observational study of premalaria season iron status and subsequent malaria morbidity Gambia N = 317

Susceptibility to malaria was not correlated with preseason serum iron serum iron-binding capacity or serum ferritin

Children who had a clinical attack of malaria with high levels of parasitemia tended to have higher mean serum ferritin levels at baseline

Shipton [6]

MSc dissertation London School of Hygiene and Tropical Medicine 2004 (unpublished)

6ndash36 mo retrospective clinic records Gambia N = 1072

Anemic children were marginally more suscep-tible to malaria than nonanemic children

Children who were iron supplemented were not more susceptible to malaria

Nyakeriga [4]

J Infect Dis 2004 8 mondash8 yr 2 cross-sectional surveys Kenya N = 234

Incidence of clinical malaria was lower in iron-deficient children (IRR = 07)

IRR of malaria was associated with plasma fer-ritin

Iron status markers were associated with malar-ia-specific IgGs

No difference in parasite density in patients with incident malaria between iron-deficient and non-iron-deficient groups

Hb hemoglobin IRR incidence-rate ratio IgG immunoglobulin Significant differences as reported by the authors

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S526 A M Prentice et alTa

ble

2 P

ublis

hed

tria

ls of

ora

l iro

n su

pple

men

tatio

n an

d m

alar

ia ri

sk

Firs

t aut

hor

Sour

ce a

nd y

ear

Stud

y de

sign

Mal

aria

at b

asel

ine

Iron

stat

us in

clus

ion

crite

ria

Cas

e de

tect

ion

and

trea

tmen

t of m

alar

ia

inci

dent

cas

esFi

ndin

gs

Mur

ray

[10]

BMJ 1

978

11ndash6

0 yr

sin

gle-

blin

d RC

T ir

on (9

00 m

g fe

rrou

s sul

fate

) vs

plac

ebo

N =

137

Excl

uded

par

asite

mic

su

bjec

tsH

b lt

11A

ctiv

e ca

se d

etec

tion

no

dat

a on

trea

tmen

tIn

terv

entio

n gr

oup

had

incr

ease

d H

b (3

6 g

dL

) and

tr

ansf

errin

and

incr

ease

d cl

inic

al m

alar

ia at

tack

s (O

R =

147

9)

Har

vey

[26]

Am

J Tr

op M

ed H

yg

1989

8ndash12

yr

iron

(200

mg

ferr

ous s

ulfa

te) v

s pl

aceb

o N

= 3

18

70

par

asite

mic

at

base

line

Hb

8ndash12

gd

L A

ctiv

e m

orbi

dity

re

ferr

al to

hea

lth

faci

lity

Diff

eren

ces i

n m

alar

ia p

ara-

sitem

ia at

bas

elin

e be

twee

n pl

aceb

o an

d in

terv

entio

n

mak

e fin

ding

s diff

icul

t to

inte

rpre

t0

6 g

dL d

iffer

ence

in

Hb

betw

een

grou

psPe

rcen

tage

of c

hild

ren

with

pa

rasit

emia

dec

reas

ed in

bo

th g

roup

s Pe

rcen

tage

with

pa

rasit

emia

in ir

on g

roup

re

mai

ned

high

er th

an th

at in

pl

aceb

o gr

oup

Aut

hors

con-

clud

e th

at ir

on th

erap

y ha

s no

effe

ct o

n m

alar

ia

Smith

[11]

Ann

Tro

p Pa

edia

tr

1989

6 m

ondash5

yr i

ron

(3ndash

6mg

kg fe

rrou

s su

lfate

) vs

plac

ebo

N

= 2

13

Dat

a no

t ava

ilabl

eH

b 5ndash

11 g

dL

Act

ive

mor

bidi

ty

surv

ey b

ut li

mite

d ac

cess

to m

edic

al

faci

litie

s

Iron

supp

lem

enta

tion

incr

ease

d H

b M

CV

seru

m ir

on t

rans

-fe

rrin

satu

ratio

n se

rum

fer-

ritin

In

crea

sed

feve

r ass

ocia

ted

with

pa

rasit

emia

OR

= 6

47

Chi

ppau

x [1

5]Bu

ll So

c Pat

hol E

xot

1991

6ndash36

mo

iron

(25

m

gkg

ferr

ous s

ulfa

te)

vs p

lace

bo N

= 2

20

Appr

ox 6

0 p

ara-

sitem

ic at

bas

elin

eH

b ge

8 g

dLA

ctiv

e tr

eatm

ent o

f m

alar

ia in

cide

nt c

ases

OR

for m

alar

ia-p

ositi

ve sm

ear

= 1

28 (N

S)

Law

less

[20]

J Nut

r 199

46ndash

11 y

r iro

n (1

50 m

g fe

rrou

s sul

fate

) vs

plac

ebo

N =

87

Dat

a no

t ava

ilabl

e75

h

ad H

b lt

12 g

dL

at b

asel

ine

Dat

a no

t ava

ilabl

eIr

on su

pple

men

tatio

n in

crea

sed

seru

m fe

rriti

n by

16

5 microg

L

vs p

lace

bo

No

diffe

renc

es in

pre

vale

nce

of

mal

aria

afte

r sup

plem

enta

tion

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S527Iron metabolism and malariaM

enen

dez [

23]

Tran

s R S

oc T

rop

Med

H

yg 1

994

Mul

tigra

vid

preg

nant

w

omen

iro

n (2

00 m

g fe

rrou

s sul

fate

) vs

plac

ebo

N =

550

Dat

a no

t ava

ilabl

ePC

V gt

25

Mea

n H

b =

10g

dL at

ba

selin

e

Act

ive

trea

tmen

t of

mal

aria

inci

dent

cas

esD

ecre

ased

pre

vale

nce

of

anem

ia a

nd o

f iro

n de

fi-ci

ency

Ir

on su

pple

men

tatio

n w

as n

ot

signi

fican

tly a

ssoc

iate

d w

ith

susc

eptib

ility

to p

reva

lenc

e or

se

verit

y of

mal

aria

van

Hen

sbro

ek [2

4]Tr

ans R

Soc

Tro

p M

ed

Hyg

199

56

mondash

9 yr

chl

oro-

quin

e vs

SP

+ ra

n-do

miz

atio

n to

iron

(asymp

100

mg

elem

enta

l iro

n) v

s fo

late

vs

pla-

cebo

N =

530

All

child

ren

wer

e re

crui

ted

at cl

inic

w

ith u

ncom

plic

ated

m

alar

ia

74

had

Hb

lt 11

g

dL at

bas

elin

eA

ll ch

ildre

n re

ceiv

ed

trea

tmen

t for

mal

aria

as

par

t of t

he tr

ial

Iron

gro

up h

ad m

ean

incr

ease

in

Hb

= 0

81 g

dL

Fola

te su

pple

men

tatio

n di

d no

t im

prov

e he

mat

olog

ical

pa

ram

eter

s and

incr

ease

d ra

te

of tr

eatm

ent f

ailu

re in

chil-

dren

rece

ivin

g SP

Ir

on d

id n

ot a

ffect

susc

eptib

il-ity

to m

alar

ia

Nw

anya

nwu

[17]

Ann

Tro

p M

ed P

aras

i-to

l 199

6lt

5 yr

SP

vs S

P +

daily

iron

(25

mg

kg fe

rrou

s sul

fate

) vs

SP

+ w

eekl

y iro

n

N

= 2

22

Incl

usio

n cr

iterio

n

para

site

dens

itygt

500

microl w

hole

blo

od

Hb

ge 5

gdL

All

wer

e tr

eate

d w

ith

SPD

aily

iron

+ S

P H

b in

crea

sed

49

gdL

vs

35ndash

37

gdL

in

SP a

nd S

P +

wee

kly

iron

G

reat

est b

enef

it on

Hb

in H

b gr

oup

5ndash8

gdL

at b

asel

ine

Iron

gro

ups h

ad in

crea

sed

trea

tmen

t fai

lure

vs

SP a

lone

(N

S)

van

den

Hom

berg

h [1

9]

J Tro

p Pe

diat

r 199

6lt

30 m

o ir

on (2

00

mg

ferr

ous s

ulfa

te) +

fo

late

vs

fola

te o

nly

N =

100

Onl

y in

clud

ed ch

il-dr

en w

ith p

aras

ite-

posit

ive

thic

k fil

ms

Hb

le 5

gdL

All

rece

ived

trea

tmen

t w

ith S

P +

quin

ine

40

rece

ived

blo

od tr

ans-

fusio

n

Diff

eren

ces i

n ba

selin

e ch

arac

-te

ristic

s (H

b p

aras

ite d

ensit

y be

twee

n gr

oups

)N

o sig

nific

ant d

iffer

ence

in

chan

ge in

Hb

betw

een

grou

psN

o di

ffere

nces

in m

alar

ia in

di-

ces b

etw

een

grou

ps

Men

ende

z [22

] La

ncet

199

72ndash

12 m

o ir

on (2

mg

kg fe

rrou

s gly

cine

sul-

fate

) + D

elta

prim

vs

iron

vs D

elta

prim

vs

plac

ebo

N =

832

24

of c

hild

ren

wer

e pa

rasit

emic

at b

ase-

line

PCV

gt 2

5Pa

ssiv

e ca

se d

etec

tion

plus

hig

h us

e of h

ealth

se

rvic

es

Iron

supp

lem

enta

tion

decr

ease

d an

emia

by

288

and

mal

aria

chem

opro

phy-

laxi

s dec

reas

ed a

nem

ia b

y 60

5

Iron

supp

lem

enta

tion

had

no

effe

ct o

n fr

eque

ncy

of m

alar

iaco

ntin

ued

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S528 A M Prentice et al

Berg

er [

14]

Eur J

Clin

Nut

r 200

06ndash

36 m

o iro

n (2

ndash3

mg

kg ir

on b

atai

n-at

e) v

s pl

aceb

o

N

= 1

97

62

of c

hild

ren

wer

e pa

rasit

emic

at

base

line

Hb

ge 8g

dL

Act

ive

mor

bidi

ty

follo

w-u

p an

d tr

eat-

men

t of a

ll fe

vers

w

ith a

ntim

alar

ials

Prev

alen

ce o

f iro

n-de

ficie

ncy

anem

ia d

ecre

ased

in ir

on

grou

p an

d in

crea

sed

in p

la-

cebo

gro

upA

ll m

arke

rs o

f iro

n st

atus

wer

e sig

nific

antly

hig

her i

n iro

n gr

oup

Incr

ease

in p

erce

ntag

e of

chil-

dren

with

par

asite

mia

gt 3

000

in

iron

gro

up (N

S)

Verh

oef [

18]

Lanc

et 2

002

2ndash36

mo

iron

(6 m

gkg

wk

ferr

ous f

uma-

rate

) vs

SP v

s iro

n +

SP v

s pl

aceb

o

N

= 3

28

Onl

y as

ympt

omat

ic

mal

aria

incl

uded

(3

0 d

ipst

ick

posi-

tive

at b

asel

ine)

Hb

6ndash11

gd

L A

ctiv

e fo

llow

-up

of

feve

rs a

nd tr

eatm

ent

upon

dia

gnos

is

SP a

lone

incr

ease

d H

b by

03

1 g

dLIr

on +

SP

incr

ease

d H

b by

11

1 g

dLIr

on a

lone

incr

ease

d H

b by

10

7 g

dLIn

crea

se in

mal

aria

risk

with

iro

n su

pple

men

tatio

n (N

S)

Des

ai [1

6]J I

nfec

t Dis

2003

2ndash36

mo

IPT

+ iro

n (3

ndash6 m

gkg

ferr

ous

sulfa

te) v

s iro

n vs

IP

T vs

pla

cebo

N

= 5

46

26

of c

hild

ren

wer

e pa

rasit

emic

at b

ase-

line

(are

a of

hig

h IT

N u

se

Hb

7ndash10

9 g

dL

Pass

ive

surv

eil-

lanc

e sy

stem

and

ac

tive

trea

tmen

t of

mal

aria

and

ane

mia

(4

-wee

kly

visit

s)

Iron

gro

up h

ad m

ean

incr

ease

in

Hb

of 0

88g

dL

Ir

on +

IPT

mea

n in

crea

se in

H

b =

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gd

LIn

crea

se in

mal

aria

par

asite

mia

(N

S) H

R =

114

N

o ef

fect

on

HR

of cl

inic

al

mal

aria

Meb

raht

u [2

1]J N

utr 2

004

4ndash71

mo

iron

(10

mg

ferr

ous s

ulfa

te) v

s iro

n +

meb

enda

zole

vs

meb

enda

zole

+

plac

ebo

vs p

lace

bo

supp

lem

ente

d fo

r 12

mo

N =

614

84

of c

hild

ren

wer

e pa

rasit

emic

at

base

line

94

had

Hb

lt 11

gd

LA

ctiv

e su

rvei

llanc

e no

trea

tmen

tIn

crea

sed

seru

m fe

rriti

nD

ecre

ased

zinc

pro

topo

rphy

rin

in su

pplem

ente

d gr

oup

N

o di

ffere

nce

in m

alar

iom

etric

in

dice

s (pr

eval

ence

or p

ara-

sitem

ia)

but c

linic

al v

alue

s no

t ass

esse

d

Tabl

e 2

Pub

lishe

d tr

ials

of o

ral i

ron

supp

lem

enta

tion

and

mal

aria

risk

Firs

t aut

hor

Sour

ce a

nd y

ear

Stud

y de

sign

Mal

aria

at b

asel

ine

Iron

stat

us in

clus

ion

crite

ria

Cas

e de

tect

ion

and

trea

tmen

t of m

alar

ia

inci

dent

cas

esFi

ndin

gs

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S529Iron metabolism and malaria

partly explain the variations in response to iron supple-mentation reported by different studies other potential complicating factors that contribute to these variations are described in table 4

All but two studies [15 19] have found significant positive effects on markers of iron status in those receiving iron supplementation In the trial of van den Hombergh et al [19] the sample size was limited and baseline characteristics were significantly different between the supplementation and placebo groups Chippaux et al [15] found that anemic children who remained parasite free had increased hemoglobin levels postsupplementation but those that subsequently developed malaria did not The effect of supplementa-tion on hemoglobin concentrations ranged between 06 and 49 gdL with the highest increase occurring in a study that combined iron supplements with anti-malarial therapy [17] Other studies have also shown an additional advantage of iron plus antimalarials as regards hemoglobin recovery [16 18] However despite the hematological benefits all of these studies found nonsignificant increases in adverse malarial outcomes in the groups that received antimalarials plus iron including increased parasite density [16] risk of malaria [18] and treatment failure [17]

Six studies found no effect of iron supplements on malaria risk [19ndash24] of these three included large proportions of anemic subjects (74 to 94) [20 21 24] and one included only children with hemoglobin lt 5 gdL [19] Other studies that stratified by baseline hemoglobin levels [17 25] found that the greatest ben-efits occurred in the most anemic subgroups

Three studies found an increase in clinical malaria attacks in the iron-supplemented groups [10 11 25] and a further six studies found nonsignificant increases in malaria outcomes [14ndash18 26] One of the striking differences between study populations with significant increases in malaria outcomes and those with non-significant effects is access to health care and active treatment of malaria incident cases In fact all but one of the trials [21] that found no effect on malaria outcomes provided access to health care facilities or active follow-up and treatment of malaria incident cases This implies that the potential detrimental effects of iron supplementation may be curtailed by concurrent effective treatment of malaria infections However Verhoef et al and Nwanyanwu et al have shown potential treatment failure effects of combining sulfadoxinendashpyrimethamine with iron in the treatment of preexisting malaria suggesting that antimalarial therapy should precede supplementation [2 17 18]

These observations are further confirmed by a large study in Zanzibar by Sazawal et al [25] that showed increases in malaria-related morbidity and mortality in the iron-supplemented arms of a randomized control-led trial of ironfolate and ironfolate plus zinc versus placebo (summarized in table 2) A subgroup of this Sa

zaw

al[2

5]La

ncet

200

61ndash

35 m

o ir

on (1

25

mg)

+ fo

late

vs

iron

+ fo

late

+ zi

nc v

s pl

aceb

o m

orbi

d-ity

and

mor

talit

y ou

tcom

es a

sses

sed

N

= 3

215

5

43

wer

e pa

rasit

emic

at

bas

elin

eH

b gt

7 g

dL 5

7 o

f ch

ildre

n ha

d H

b lt

10 g

dL

at b

asel

ine

Trea

ted

subs

tudy

chil-

dren

with

clin

ical

m

alar

ia w

ith S

P at

ba

selin

e 6

mo

and

12

mo

Com

bine

d iro

n gr

oups

vs

pla-

cebo

Fo

r adv

erse

mal

aria

-rel

ated

ev

ents

RR

= 1

16

For c

ereb

ral m

alar

ia R

R =

122

Iron

+ fo

late

vs

plac

ebo

For c

ereb

ral m

alar

ia a

s a c

ause

of

dea

th R

R =

17

Subs

tudy

Lo

wer

rate

of a

dver

se e

vent

s in

child

ren

iron

defic

ient

at

base

line

Prot

ectiv

e ef

fect

of i

ron

+ fo

late

in

iron

-def

icie

nt a

nem

ic ch

il-dr

en R

R =

051

Sig

nific

ant d

iffer

ence

s as

repo

rted

by

the

auth

ors

RCT

ran

dom

ized

con

trol

led

tria

l H

b h

emog

lobi

n O

R o

dds

ratio

MC

V m

ean

corp

uscu

lar

volu

me

NS

not

sig

nific

ant

PCV

pac

ked

cell

volu

me

SP

sul

fado

xine

ndashpyr

imet

ham

ine

IPT

inte

rmitt

ent

prev

entiv

e th

erap

y IT

N i

nsec

ticid

e tr

eate

d be

dnet

s ]H

R h

azar

d ra

tio R

R re

lativ

e ris

k

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S530 A M Prentice et al

trial was investigated in more detail and consequently received more intensive diagnosis and treatment of malaria and other infections Substudy children with iron-deficiency anemia at baseline benefited sig-nificantly from iron supplementation in that they had reduced malaria and other infection-related hospital admissions and mortality [25]

The results of this recent study in Zanzibari children have raised new concerns about possible serious side effects of iron supplementation in populations where the etiology of anemia is not solely attributable to iron

deficiency and point to the need for a deeper under-standing of the complex biology of iron sequestration and redistribution between different storage and functional compartments and of the underlying host factors that influence these processes

Effect of malaria on iron metabolism

Erythropoietic iron requirement is met largely through recycling of senescent red blood cells through reticu-loendothelial macrophages where iron is repackaged onto transferrin for transport to the bone marrow [27] Red blood cells are predominantly engulfed directly by reticuloendothelial macrophages however up to 10 of normal recycling occurs as a result of intravascular hemolysis Hemoglobin is released and rapidly bound to haptoglobin and the resultant complex is cleared by liver parenchymal cells or the CD163 macrophagal receptor [28] Malaria-induced destruction of infected and noninfected red blood cells both stresses and impedes the capacity of reticuloendothelial macro-phages to recycle iron back to the bone marrow Intra-vascular rupture of parasitized red cells macrophagal phagocytosis of both parasitized and unparasitized red cells and hypersplenism all contribute to the patho-physiology of the anemia associated particularly with acute malaria

The local epidemiology and transmission character-istics of Plasmodium falciparum together with local drug treatment and intermittent preventive therapy

TABLE 3 Meta-analyses and reviews

First author Sourceyear Study design Findings

Shankar [87] J Infect Dis 2000 Meta-analysis of 13 RCTs of the effect of iron supplementation on malaria and iron status

RR for clinical malaria attack = 11 (NS)RR for slide positive for Plasmodium falci-

parum = 117Absolute increase in infection rate = 57 (NS)RR for spleen enlargement = 112 (NS)Mean increase in Hb = 125 gdLRR for anemia = 05

Oppenheimer [2] J Nutr 2001 Review of controlled interven-tion studies of iron supplemen-tation

Oral iron therapy increased clinical malaria in 5 out of 9 studies

No studies of iron therapy in malarious areas showed benefits on infectious morbidity

Does not report on effect on iron status

Gera [88] BMJ 2002 Systematic review of 28 RCTs of the effect of iron supplementa-tion or fortification in children on infectious illness (including 8 studies of the effect of iron supplementation on malaria)

Pooled OR for malaria-positive smear = 143 but OR when adjusted for baseline malaria smear = 124 (NS)

(The treatment effect increased by 289 times per unit increase in baseline malaria posi-tivity this supports the argument that iron supplementation of children with preexist-ing malaria increases their risk of remaining malaria positive)

Significant differences as reported by the authors RCT randomized controlled trial RR relative risk NS not significant Hb hemoglobin OR odds ratio

TABLE 4 Factors complicating assessment of the relationship between iron status and malaria and the response to iron sup-plementation in malaria-endemic populations

raquo Differences in dose duration and route of iron admin-istration

raquo Degree of malaria immunity in study individuals which can also be related to age and local malaria transmission patterns [7]

raquo Supplementation with iron and folate vs iron alone (especially as some antimalarials have antifolate action) [24]

raquo Markers of iron status used (the confounding effect of infection on serum markers of iron deficiency) [2 8]

raquo Baseline iron status iron-deficient individuals benefit [18 21]

raquo Access to health care and intensity of malaria surveil-lance and treatment during the trial [18 25]

raquo Hemoglobinopathies may affect anemia and response to iron supplementation as well as risk of malaria [9 73]

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S531Iron metabolism and malaria

(IPT) practices influence population immunity and resultant malarial clinical presentation as well as the epidemiology of anemia in a particular setting These factors may also influence the disturbance of iron metabolism and erythropoietic response to iron sup-plementation Acute malaria is associated predomi-nantly with a picture of fever hemolysis and oxidant stress whereas dyserythropoiesis predominates in the anemia of chronic malaria in a semiimmune patient [29] Acute malarial hemolysis represents a major stress on the homeostatic mechanisms of iron flux regulation that have evolved primarily to maintain erythroblast supply while minimizing the oxidant stress-associated effects of iron

Iron can be sequestered and trapped in reticuloen-dothelial macrophages as a result of both chronic and acute malaria and can present a picture of iron-deficient erythropoiesis associated with normal or increased bone marrow iron For instance bone marrow aspirates in 23 Thai patients with uncomplicated acute malaria (age 15 to 52 years) demonstrated malarial pigment in 22 of them Convalescent bone marrow aspirates in 16 patients (3 to 25 days after admission) demonstrated increased iron content compared with the admission sample [30] Five of six Gambian children (lt 5 years of age) with acute malaria had elevated stainable bone marrow iron and four of six children with chronic malaria and severe anemia (hemoglobin lt 6 gdL) had either normal or markedly increased levels of bone marrow stainable iron [31] Eighty-six percent of Indian children and adults (N = 26) with acute and 84 of those with chronic falciparum malaria and anemia (mean hemoglobin 54 gdL N = 38) had normal or increased bone marrow iron stores [32] Ferrokinetic studies involving the intravenous administration of 59Fe demonstrated low unsaturated iron-binding capacity and a rapid plasma iron disappearance time in both parasitemic and postparasitemic patients with acute and secondary (recent acute infection with persistent parasitemia) P falciparum and P vivax in Thai adults compared with controls [33] Incorporation of 59Fe into red blood cells was decreased in acute (N = 5) and secondary parasitemia (11 of 14) but found to be largely normal in the postparasitemic patients includ-ing 3 who were restudied from the parasitemic group Iron sequestration in acute malaria is cytokine driven (elevated tumor necrosis factor α [TNF-α] ILndash1 and interferon γ [IFN-γ] and diminished ILndash10) [29] prob-ably mediated via hepcidin however quantifying this phenomenon assessing how long it persists after acute malaria and in association with chronic malaria and assessing its importance in relation to malarial anemia malaria-associated immunosuppression and response to iron supplementation is difficult since there are few data Conventional indices of iron storage (eg ferritin) or of tissue supply (eg zinc protoporphyrin soluble transferrin receptor transferrin saturation) are

affected by inflammation [8 34ndash36] and the assess-ment of the iron status of young children in malarious areas with acute or chronic malaria is problematic [34] In a holoendemic environment ferritin and eryth-rocyte protoporphyrin were not affected by chronic malaria in older children [37] These indices also do not distinguish between iron deficiency and iron sequestration

Effect of malaria on response to iron supplementation

Malaria-induced anemia does not lead to loss of iron from the body However iron deficiency often coex-ists with malaria in areas of malaria transmission and therapy for severe postmalarial anemia commonly assumes a component due to preexisting iron defi-ciency Iron supplements are routinely prescribed both for severe malaria-associated anemia and for presumed iron-deficient anemia in a malaria-endemic environ-ment Few studies however have looked at the effect of acute malaria on the response to iron supplementation and even fewer have addressed the effect of chronic asymptomatic malaria More commonly studies either have either assessed the response to supplementation of children with anemia of undefined etiology in areas of coexistent malaria iron deficiency and hookworm or have randomized children who were anemic after malaria to a variety of hematinics In a study of 222 Malawian children (lt 5 years of age) with anemia after acute malaria the use of Fansidar and daily supplemen-tal iron resulted in a significantly greater hemoglobin recovery than Fansidar alone or Fansidar and weekly iron only in those children with initial hemoglobin between 5 and 8 gdL [17] However a larger propor-tion of the iron-treated children failed to clear their malaria In the Gambia 600 children (mean age 52 months mean hemoglobin 96 gdL) with uncompli-cated falciparum malaria randomized to receive chlo-roquine or Fansidar as treatment and then either iron folic acid or placebo for 28 days [22] demonstrated a significantly better hemoglobin response with iron than with placebo or folic acid (the difference in mean hemoglobin level after 1 month was 07 gdL) One hundred Tanzanian children (lt 30 months of age) with severe anemia (hemoglobin lt 5 gdL) were randomized either to receive daily iron supplementation or to be controls after antimalarial treatment [19] Among the 60 who completed the 12-week follow-up without a transfusion (30 in each group) there were no differ-ences in hemoglobin recovery From these studies the role of iron supplementation in the treatment of anemia after acute malaria is unclear and it is likely that the hemoglobin response to supplementation is influenced by both the direct inflammatory effect of malaria on iron absorption and utilization and preexistent iron

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S532 A M Prentice et al

deficiency which is impossible to assess in the presence of malaria In the Gambia we recently compared the absorption of stable-isotope-labeled iron in children anemic as a result of iron deficiency and children anemic after acute malaria Both groups were given 30 days of iron supplementation and the malaria group demonstrated significantly better hemoglobin recovery despite initially significantly reduced iron absorption (Doherty et al unpublished results) Utilization of sequestered iron is likely to be a major contributor to erythroblastic iron requirement after acute malaria

Studies of iron supplementation of populations of anemic children in malarious areas have reported either improved hemoglobin response or decreased prevalence of severe anemia [16 22 38 39] Incorpo-ration of antimalarial intervention arms is common Malaria transmission characteristics study design use of antecedent antimalarials differing iron supplemen-tation doses and differing outcome measures as well as different prevalence rates of iron deficiency and hook-worm infection have made the assessment of factors affecting hemoglobin response to iron supplementation difficult In particular the effect of chronic malaria on response to supplementation in high-transmission areas is unclear as the etiology of the anemia and the chronicity of malaria parasitemia are often undefined in study subjects In an area of intense transmission in Tanzania in which more than 80 of children (4 to 71 months old) were parasitemic at baseline and where malaria infection was strongly associated with hemo-globin supplementation improved the iron status and motor and language development of an iron-deficient population but not did not improve hemoglobin [21 36 40] The authors concluded that factors including malarial parasitemia or ineffective erythropoiesis due to inflammatory processes in a population with high levels of infectious morbidity and inflammation might have limited erythropoiesis

An inflammatory-mediated block to iron absorp-tion and utilization is likely to limit the erythropoietic response to supplemental iron after acute malaria how-ever it is unclear whether chronic parasitemia similarly limits the response to supplemental iron The asso-ciation of chronic malaria with anemia [39] stainable bone marrow iron [34] and increased cytokine levels [41] might suggest a probable effect and the eradica-tion of parasites has been associated with hemoglobin improvement without supplemental iron [31]

Iron metabolism by malaria parasites

In this section we consider whether the availability of iron in the host could modulate the efficiency with which malaria parasites can establish an infection and the severity of that infection What evidence is there to support the ldquonutritional immunityrdquo hypothesis that

host iron availability could limit parasite invasion or multiplication andor the clinical sequelae of para-site infection Support for the nutritional immunity hypothesis first stated in the 1970s has generally waned for the majority of pathogens [2] but there may still be a case for obligate intracellular pathogensmdashincluding Plasmodium spp

It may be informative to examine the research of other scientists than those typically involved in the cur-rent debate For example in order for this hypothesis to be truemdashat least in terms of the success of parasite invasion and replicationmdashit is a requirement that P falciparum be dependent on host iron sources for its survival Next is iron deficiency ever likely to be a limiting factor in the supply of iron to the parasite The most recent research suggests that P falciparum does utilize iron from the host but not from the abundant supplies available in erythrocyte hemoglobin the heme portion of which is quickly degraded to nontoxic but non-iron-bioavailable hemozoin or from the plasma via transferrin but from another source possibly an intraerythrocytic labile pool of ferrous iron [42 43] Interestingly measurements of this labile ferrous iron in normal and sickled erythrocytes indicate it to be positively associated with hemoglobin concentrations and negatively associated with plasma ferritin [44] However other researchers have reported evidence to suggest that the degradation of heme to hemozoin is incomplete and that 50 of heme may be degraded via an alternative pathway involving reduced glutathione and releasing bioavailable iron [45 46] As it has been estimated that less than 1 of heme iron would be sufficient to meet parasite iron requirements [47] iron deficiency would never induce iron-limited growth if hemoglobin were the iron source for parasites

Another mechanism by which iron deficiency may limit parasite growth is that proposed recently by Iyer et al [48] who demonstrated the inhibition of hemozoin formation from toxic free heme by the naturally occur-ring zinc protoporphyrin IX (ZPP) at levels likely to be encountered in anemic erythrocytes It is interesting to note that this is thought to be the mechanism by which the quinoline antimalarials act Furthermore Iyer et al demonstrated that quinolines competed for ZPP bind-ing and prevention of hemozoin formation It is pos-sible that via this mechanism moderate anemia could allow the persistence of low levels of parasitemia and therefore affect the development of exposure-related antibody repertoire and clinical immunitymdashwith consequent effects on future malarial incidence and malaria-associated anemia However the evidence for such an effect in human populations is currently limited due to the lack of longitudinal studies assessing ZPP levels and parasite prevalence and density from infancy onwards

Another research area that has been used to support the hypothesis of decreased iron availability is that

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S533Iron metabolism and malaria

of the effects of iron chelators on parasite growth in vitro and in vivo [49 50] Furthermore some antima-larial drugs such as the antibiotic cyclines including doxycycline are also iron chelators However iron chelators may not be acting by depriving the parasite of iron Alternative mechanisms have been suggested for some chelators including the induction of reactive oxygen species from dissociation of iron from heme and hemozoin as suggested for the lipophilic FR160 [51] similar to the suggested mechanism of artemisinin [52] Furthermore differences between the efficacy of chelators in vitro and in vivo have been associated with differences in immune modulation [53] This may suggest that iron status could affect malarial outcomes via direct effects on immune modulation as suggested by Nyakeriga et al [54] The evidence base for the effects of current iron-chelator therapies in reducing the prevalence density or clinical sequelae of malaria is weakmdashas outlined in a recent Cochrane review of clinical trials involving the use of either desferioxamine or the orally available deferiprone [55] in which all of the seven studies included had limitations relat-ing to study size relevance of study populations and more critically methodological and analytical faults However the authors of this review concluded that the results suggested possible benefits of treatment in cerebral malaria with a shorter recovery time from coma and decreased time to parasite clearance The initial justification for using iron-chelator therapy in cerebral malaria was based on the premise of prevent-ing iron-induced damage to brain cells resulting from hemolysis Therefore it is important to note that the possible benefits of iron-chelator therapy may not relate to limitation of iron for parasite growth and may there-fore not provide evidence in support of the nutritional immunity hypothesis

Iron malaria and hemoglobinopathies

How do hemoglobinopathies protect against parasite invasion or multiplication andor clinical sequelae of parasite infection Are these polymorphisms likely to affect the relationship between iron status or supple-mentation and malaria

J B S Haldane is credited with first postulat-ing heterozygote selection as an explanation for the high prevalence of the thalassemias and later other hemoglobinopathies He suggested that the small size reduced hemoglobin concentrations and increased resistance to hypertonic solutions of such cells may result in decreased parasite invasion or growth Although this hypothesis has been widely accepted for some time it has only recently been possible to dem-onstrate that these mutations have been maintained by selection mostly by malaria but possibly also other infectious causes However the extent and mechanisms

of protection are still debated At least in vitro many studies have failed to demonstrate decreased ability of parasites to invade or grow in thalassemic cells or cells containing hemoglobin S (HbS) Instead the mecha-nisms appear to be more complicated and possibly to vary between local conditions

The common polymorphisms involved in hemo-globin synthesis or red cell formation include sickle hemoglobin (HbS) HbC and HbE the α and β-thalassemias and South Asian ovalocytosis The geographic distribution of these varies across tropi-cal areas and can vary extensively even within closely related regions Current estimates of these polymor-phisms are often based on single sites and are likely to be underestimates [56] but a figure of 27 million carriers of the main hemoglobinopathies has been proposed [56] The carrier frequency for HbS is esti-mated at between 5 and 40 in populations across sub-Saharan Africa the Middle East and parts of South Asia HbC is limited to parts of West and North Africa whereas HbE is common in some parts of India and Southeast Asia with carrier rates up to 60 The thalassemias have the broadest geographic distribution and also the widest range of causative mutations and clinical outcomes The carrier frequencies for the more severe range of β-thalassemias is generally lower than for the α-thalassemias which are estimated to reach carrier frequencies of up to 20 in sub-Saharan Africa higher in Middle Eastern and Indian populations and up to 80 in some Pacific populations (reviewed in Williams et al [57] Rees et al [58] and Maitland et al [59])

In β-thalassemias excess α-globin chains precipitate in red cell precursors leading to ineffective erythropoi-esis and resulting in anemia in the context of increased iron absorption and iron accumulation The clinical expression of β-thalassemia varies widely depending on the exact genetic lesions inherited and interactions with other genetic loci including the α and γ globin genes β-Thalassemia trait and β-thalassemia interme-diate are often asymptomatic and may not be diagnosed except for mild anemia In α-thalassemia the excess β-chains form stable homotetramers which do not sig-nificantly affect erythropoiesis but cause an increased rate of hemolysis of mature cells The degree of the deficit of α-globin chains depends on the number of α-globin genes inactivated and unless three α-globin genes are lost the effects are subtle and various so that the condition will go largely undiagnosed It might be supposed that iron supplementation could be more deleterious in populations with a high prevalence of β-thalassemia mutations because of the inability to utilize the iron leading to increased iron availability to pathogens or iron-induced oxidant stress Interest-ingly Oppenheimer [2] reported that the increased susceptibility to malaria associated with parenteral iron in Papua New Guinean children was not apparent in

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S534 A M Prentice et al

single-deletion α-thalassemia compared with normal children

In a prospective casendashcontrol study in Papua New Guinea α-thalassemic α+ndash homozygotes and α+ndash heterozygotes had a greatly decreased risk of severe malaria (incidence rate ratio = 04 and 066) compared with controls [9] Furthermore protection was also observed for hospitalization from other infections possibly suggesting an immune component to the pro-tection [60] although the reduction of severe malaria may reduce infectious sequelae by invasive bacte-rial disease In apparent contrast α-thalassemia has also been associated with an increased prevalence of uncomplicated malaria in Vanuatu particularly in very young children with P vivax [57] It was suggested that increased red cell turnover in these children increased susceptibility to P vivax [58] resulting in cross-species immunity to P falciparum in later life [59] A similar finding was reported for glucose-6-phosphate dehy-drogenase (G6PD) deficiency in a cohort study in Uganda in which many other potential risk factors for malarial infection were controlled for (age water source use of prophylaxis bednet usage and proxim-ity to mosquito breeding sites) Female heterozygotes for G6PD had a significantly increased incidence of uncomplicated malaria (IRR = 13 p = 03) and a trend for increased parasite densities similar trends were seen for hemizygote males This was different from the pattern observed for HbS heterozygotes who had a nonsignificantly decreased incidence of uncomplicated malaria and decreased parasite densities [61]

A mechanism that has been suggested for G6PD defi-ciency and that may also be applicable to sickle (HbAS) and thalassemic cells involves decreased oxidative protection (G6PD) or increased constitutive oxidative stress of these cells (HbAS αβ thalassemias) especially when infected resulting in increased clearance of the cells from non-malaria-specific immune mechanisms essentially the same as the normal removal of old ldquosenescentrdquo red cells by phagocytes [62ndash64] It has been proposed that such a mechanism could prevent parasitemias from reaching critically high densities and therefore protect from severe malaria and also facilitate the development of antibody repertoires in children from the maintenance of low-grade infections in young children [65ndash67] In a slight modification of this hypothesis the increased phagocytic removal of early ring-stage infected cellsmdashcompared with schizonts and trophozoitesmdashhas been demonstrated for G6PD β-thalassemic and HbAS cells in vitro but not for α-thalassemic infected cells [68] The phagocytosis of ring compared with later stages may be advantageous since rings contain less hemozoin the buildup of which in monocytes has been associated with decreased func-tion Additionally the reduction of the later stages of parasite development may reduce the development of severe symptoms such as cerebral malaria from

reduced endothelial adhesion of late-stage infected red blood cells to receptors such as intracellular adhesion molecule-1 (ICAM-1)

The epidemiological evidence for a protective effect of HbAS suggests that the protective effects are great-est for severe disease (reviewed by Roberts et al [69]) In the most comprehensive study to date a detailed prospective cohort in two Kenyan populations it was reported that HbS heterozygotes had a significantly decreased risk of mild clinical malaria as assessed by active surveillance (50 decreased risk 95 confi-dence interval [CI] 26 to 67]) a 75 (95 CI 84 to 61) decreased risk of hospital admission for malaria and a 90 [95 CI 3 to 99] decreased risk of severe malaria (severe malarial anemia cerebral malaria or complicated malaria) [70] There was no effect of HbAS on the risk of asymptomatic infec-tions or of parasite density in asymptomatic infections assessed at four cross-sectional surveys There were significant decreases in parasite densities for all of the other categories of infection Additionally in this study unlike another in western Kenya [71] the protection was specific to malaria and did not extend to other common childhood infections including respiratory infections gastroenteritis and helminth infections

What influence the hemoglobinopathic and other polymorphisms may have on the effect of iron sup-plementation on malarial susceptibility is potentially dependent on the extent and mechanisms of protection from infection in the different genotypesmdashinfluences that are likely to be further complicated by differential effects according to age and malarial exposure and effects of coinheritance [72] The coinheritance of the HbS G6PD deficiency and α-thalassemia deletion alle-les is likely to be prevalent in sub-Saharan populations making the study of such effects in real populations extremely difficult by requiring very large sample sizes and complex statistical modeling

To the authorsrsquo knowledge only two published randomized controlled trials of iron supplementation have assessed the effects by genotypemdashin both cases by HbAS versus HbAA [73 74]

In the first trial involving Traditional Birth Attend-ant-administered routine iron supplementation to multigravid Gambian pregnant women Menendez et al [73] reported that although overall there were significant beneficial effects on hemoglobin and packed cell volume (PCV) and on birthweight these effects were entirely accounted for by women with the HbAA phenotype (N = 402 vs N = 98) whereas iron-supplemented HbAS women had lower HB PCV and birthweight than HbAA women receiving placebo Furthermore even in this relatively small study these interactions were statistically significant (p lt 01 for hematological indices at delivery baseline measurements as a covariate p lt 03 for birthweight maternal height included as a covariate) Overall

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S535Iron metabolism and malaria

there was no reported increase in susceptibility to malaria as assessed by the prevalence of peripheral malaria at late pregnancy and delivery or by placental histology Yet iron-supplemented HbAS women had an increased prevalence of placental malaria (76 [2229]) compared with iron-supplemented HbAA women (53 [83158]) placebo-treated HbAA women (59 [91154]) or placebo-treated HbAS women (58 [1933]) At the time of this study IPT prophylaxis was recommended only for primigravid pregnant women in the Gambia hence the choice of the study population What the effects of iron supplementation might be in either primigravidae or multigravidae receiving IPTmdashwhich is now recommended for all pregnant women in malaria-endemic countriesmdashhas not been assessed The protection afforded by the HbAS genotype is likely to vary according to gravidity and malarial endemic-ity In areas of high transmission the majority of the increased risk is borne by primigravidae whereas in areas of lower and highly defined seasonal transmis-sion the increased risk extends to a greater number of pregnancies [75] The protective effect of HbAS is thought to be greatest in relatively nonimmune young children who have not yet developed acquired immunity by exposure to a variety of clonal variants of P falciparum and therefore have not developed a full antibody repertoire to the variant surface antigens (VSA) expressed on the cell surfaces of parasitized red blood cells

In the second trial the effect of the HbAS phenotype on the response to iron supplementation in children was assessed in a subanalysis of a 2 times 2 randomized controlled trial of iron supplementation and inter-mittent preventive treatment (IPT) for malaria using sulfadoxinendashpyrimethamine in anemic Kenyan chil-dren (hemoglobin 7 to 109 gdL) [74] There was no reported increase in the susceptibility to clinical malaria or the prevalence of parasitemia at monthly screening associated with the iron supplementation alone or with IPT [16] whereas IPT plus iron was the most effective in increasing hemoglobin concentrations There were no significant statistical interactions between HbASAA phenotypes and treatment group However there was a nonsignificant increase in the incidence rate ratio of clinical malaria in the HbAS group not receiv-ing IPT during the 12 weeks of follow-up (IRR = 416 95 CI 05 to 346) and increased geometric mean parasite density in both groups but by far the biggest difference was seen in the group receiving IPT (6203 vs 1853 p = 08 for the interaction) The authors acknowledge that the number of clinical events was very small and that these findings would need veri-fication in a larger study since the number of HbAS individuals (approximately 25 to 30) in each treatment group versus approximately 100 HbAA individuals plus the short follow-up time means that the study was grossly underpowered to assess these outcomes If this

effect is real then the age group studied in this trial (2 to 36 months with 78 lt 18 months) should include the most affected although greater effects might be observed in areas of lower transmission and therefore also in a greater age range of children The results of these two trials warrant urgent further trials or retro-spective analysis of prior trials with sufficient power and detail to make firm conclusions on the effects of common polymorphisms on the response to iron sup-plementation which may be expected to vary by age group and transmission intensity

Clinical trials of IPT during infancy (IPTi) have demonstrated a reduction in the prevalence of anemia in young children in malaria-endemic areas [16 18 38 76] and in some trials a reduction in the incidence of clinical malaria [38 76] and morbidity and mortality in the first year of life [38 77] However the effects may vary depending on the timing of dosing choice of drug local levels of resistance and levels of transmission [78 79] On the basis of our analysis above the impact of IPTi plus iron supplementation may be modulated by levels of hemoglobinopathies and therefore suba-nalyses of these studies should be performed according to genotype wherever possible

Interactions of polymorphisms in host iron metabolism and regulatory proteins with malaria

Polymorphisms of haptoglobin a plasma protein that binds free hemoglobin released from lysed red blood cells recirculating the heme portion to the bone marrow through monocyte and macrophage uptake via CD136 have also been associated with malarial outcomes although reports are conflicting Hap-toglobin exists as three common phenotypes Hp1-1 1-2 and 2-2 In case-control studies in India Sudan Ghana and Cameroon the Hp2-2 phenotype has been associated with protection from severe malaria and placental infection [80ndash83] However two studies that have assessed associations with haptoglobin genotypes did not report any associations [84 85] In a cohort study in Gambian children the Hp2-2 genotype was associated with a greater drop in hemoglobin concen-trations across a malarial transmission season [65] The authors proposed that this effect may have been mediated through an increased prevalence of asymp-tomatic infection observed in the Hp2-2 group which contributed to anemia but could provide protection against severe malaria Interestingly similar but smaller drops in hemoglobin concentration were also observed for heterozygotes for G6PD and HbS We are currently analyzing the effects of low-dose iron supplementation during a malarial transmission season in a similar cohort of children

Inducible heme oxygenase (iHO-1) catalyzes the

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S536 A M Prentice et al

breakdown of heme to generate iron carbon monoxide and biliverdin and is expressed in monocytes and mac-rophages among other cells Biliverdin is subsequently degraded to bilirubin which has potent antioxidant effects Microsatellite polymorphisms in the number of tandem repeats in the promoter of iHO-1 have been variously associated with increased and decreased oxidant stress in various disease pathologies However in a case-control study of cerebral malaria patients in Myanmar homozygotes for the short number of repeats (lt 28) previously associated with higher levels of transcription of iHO-1 were significantly more likely to have cerebral malaria than uncomplicated malaria (odds ratio 314 p = 008) [86] It is not clear how this effect may be mediated but it is possible that it results from increased levels of free iron and resulting oxidant stress

In summary the mechanisms by which various genetic polymorphisms interact with malarial infec-tion are still not clear Furthermore it is not clear how they may affect a possible relationship between iron and malaria especially in relation to supplementation which should be differentiated from that of iron status The current evidence suggests that the heterozygous states of the hemoglobinopathies do not protect against malaria by a simple mechanism involving iron with-holding from the pathogen However the effects of iron supplementation in individuals with the most common polymorphisms should be carefully evaluated taking into account differences in transmission intensity and iron status at baseline

Conclusions

The evidence reviewed above tends to substantiate the concerns raised by the recent Pemba trial that universal administration of iron to children in malarious areas may be associated with adverse outcomes The mecha-nism by which this occurs is far from clear and merits

further research to test whether other chemical forms of supplementary iron might carry less risk There is also evidence that the risk profile will be altered by host genetic variations in hemoglobinopathies G6PD and genes regulating iron metabolism However these insights are not of great practical value because population screening and targeted supplementation programs are not feasible in the areas where iron defi-ciency is most prevalent Likewise the evidence that anemic children are probably at low risk for any adverse outcomes associated with iron supplementation implies a need for prescreening that may not be cost-effective or logistically feasible in developing-country settings

The evidence is fairly clear that malaria causes anemia by diverting iron away from bone marrow and erythropoiesis as part of the inflammatory response and hence iron administration alone is not likely to be the most effective means of combating the anemia Other therapeutic paradigms that combat the inflam-mation and adjust the timing of iron administra-tion to children recovering from malaria should be researched

We suggest that further research is still required to confirm the apparent relationships between iron status and malaria and that such studies should also focus on the underlying mechanisms of the putative interaction This might be achieved through the establishment of a multicountry collaboration to standardize protocols both for iron-supplementation interventions and for the assessment of iron and malaria status indicators Standardizing protocols across variations in age groups malaria transmission patterns and genetic distribu-tions of hemoglobinopathies will provide the evidence for a more targeted approach to policies of prevention and treatment of anemia in malaria-endemic regions

Until this evidence is gathered we recommend that iron supplementation in malarious areas must be accompanied by effective systems for ensuring univer-sal rapid access to diagnosis and treatment of malaria or by preventive therapy

References

1 WHO UNICEF Focusing on anaemia Towards an integrated approach for effective anaemia control Joint WHO UNICEF Statement Geneva Joint WHO UNICEF Statement 2004

2 Oppenheimer SJ Iron and its relation to immunity and infectious disease J Nutr 2001131616Sndash33S discussion 33Sndash35S

3 Murray MJ Murray AB Murray NJ Murray MB Diet and cerebral malaria the effect of famine and refeeding Am J Clin Nutr 19783157ndash61

4 Nyakeriga AM Troye-Blomberg M Dorfman JR Alexander ND Back R Kortok M Chemtai AK Marsh K Williams TN Iron deficiency and malaria among children living on the coast of Kenya J Infect Dis 2004 190439ndash47

5 Oppenheimer SJ Macfarlane SB Moody JB Bunari O Hendrickse RG Effect of iron prophylaxis on morbidity due to infectious disease report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 1986 80596ndash602

6 Shipton D Association between haemoglobin level and susceptibility to malaria a study of Gambian children [MSc dissertation] London London School of Hygiene and Tropical Medicine 2004

7 Snow RW Byass P Shenton FC Greenwood BM The relationship between anthropometric measurements and measurements of iron status and susceptibility to malaria in Gambian children Trans R Soc Trop Med Hyg 199185584ndash9

8 Asobayire FS Adou P Davidsson L Cook JD Hurrell

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S537Iron metabolism and malaria

RF Prevalence of iron deficiency with and without concurrent anemia in population groups with high prevalences of malaria and other infections a study in Cote drsquoIvoire Am J Clin Nutr 200174776ndash82

9 Allen SJ OrsquoDonnell A Alexander ND Alpers MP Peto TE Clegg JB Weatherall DJ alpha+-Thalassemia protects children against disease caused by other infec-tions as well as malaria Proc Natl Acad Sci U S A 1997 9414736ndash41

10 Murray MJ Murray AB Murray MB Murray CJ The adverse effect of iron repletion on the course of certain infections Br Med J 197821113ndash5

11 Smith AW Hendrickse RG Harrison C Hayes RJ Greenwood BM The effects on malaria of treatment of iron-deficiency anaemia with oral iron in Gambian children Ann Trop Paediatr 1989917ndash23

12 Oppenheimer SJ Gibson FD Macfarlane SB Moody JB Harrison C Spencer A Bunari O Iron supplementation increases prevalence and effects of malaria report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 198680603ndash12

13 Byles AB Drsquosa A Reduction of reaction due to iron dextran infusion using chloroquine Br Med J 19703625ndash7

14 Berger J Dyck JL Galan P Aplogan A Schneider D Traissac P Hercberg S Effect of daily iron supplementa-tion on iron status cell-mediated immunity and inci-dence of infections in 6ndash36 month old Togolese children Eur J Clin Nutr 20005429ndash35

15 Chippaux JP Schneider D Aplogan A Dyck JL Berger J [Effects of iron supplementation on malaria infection] Bull Soc Pathol Exot 19918454ndash62

16 Desai MR Mei JV Kariuki SK Wannemuehler KA Phil-lips-Howard PA Nahlen BL Kager PA Vulule JM ter Kuile FO Randomized controlled trial of daily iron sup-plementation and intermittent sulfadoxine-pyrimeth-amine for the treatment of mild childhood anemia in western Kenya J Infect Dis 2003187658ndash66

17 Nwanyanwu OC Ziba C Kazembe PN Gamadzi G Gandwe J Redd SC The effect of oral iron therapy during treatment for Plasmodium falciparum malaria with sulphadoxine-pyrimethamine on Malawian chil-dren under 5 years of age Ann Trop Med Parasitol 199690589ndash95

18 Verhoef H West CE Nzyuko SM de Vogel S van der Valk R Wanga MA Kuijsten A Veenemans J Kok FJ Intermittent administration of iron and sulfadoxine-py-rimethamine to control anaemia in Kenyan children a randomised controlled trial Lancet 2002360908ndash14

19 van den Hombergh J Dalderop E Smit Y Does iron therapy benefit children with severe malaria-associated anaemia A clinical trial with 12 weeks supplementation of oral iron in young children from the Turiani Division Tanzania J Trop Pediatr 199642220ndash7

20 Lawless JW Latham MC Stephenson LS Kinoti SN Pertet AM Iron supplementation improves appetite and growth in anemic Kenyan primary school children J Nutr 1994124645ndash54

21 Mebrahtu T Stoltzfus RJ Chwaya HM Jape JK Savioli L Montresor A Albonico M Tielsch JM Low-dose daily iron supplementation for 12 months does not increase the prevalence of malarial infection or den-sity of parasites in young Zanzibari children J Nutr 20041343037ndash41

22 Menendez C Kahigwa E Hirt R Vounatsou P Aponte JJ Font F Acosta CJ Schellenberg DM Galindo CM Kimario J Urassa H Brabin B Smith TA Kitua AY Tanner M Alonso PL Randomised placebo-controlled trial of iron supplementation and malaria chemoproph-ylaxis for prevention of severe anaemia and malaria in Tanzanian infants Lancet 1997350844ndash50

23 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S MrsquoBoge B Greenwood BM The effects of iron supplementation during pregnancy given by traditional birth attendants on the prevalence of anaemia and malaria Trans R Soc Trop Med Hyg 199488590ndash3

24 van Hensbroek MB Morris-Jones S Meisner S Jaffar S Bayo L Dackour R Phillips C Greenwood BM Iron but not folic acid combined with effective antimalarial therapy promotes haematological recovery in African children after acute falciparum malaria Trans R Soc Trop Med Hyg 199589672ndash6

25 Sazawal S Black RE Ramsan M Chwaya HM Stoltzfus RJ Dutta A Dhingra U Kabole I Deb S Othman MK Kabole FM Effects of routine prophylactic supplemen-tation with iron and folic acid on admission to hospital and mortality in preschool children in a high malaria transmission setting community-based randomised placebo-controlled trial Lancet 2006367133ndash43

26 Harvey PW Heywood PF Nesheim MC Galme K Zegans M Habicht JP Stephenson LS Radimer KL Brabin B Forsyth K et al The effect of iron therapy on malarial infection in Papua New Guinean schoolchil-dren Am J Trop Med Hyg 19894012ndash8

27 Andrews NC Iron homeostasis insights from genetics and animal models Nat Rev Genet 20001208ndash17

28 Kristiansen M Graversen JH Jacobsen C Sonne O Hoffman HJ Law SK Moestrup SK Identification of the haemoglobin scavenger receptor Nature 2001409 198ndash201

29 Wickramasinghe SN Abdalla SH Blood and bone marrow changes in malaria Baillieres Best Pract Res Clin Haematol 200013277ndash99

30 Phillips RE Looareesuwan S Warrell DA Lee SH Karbwang J Warrell MJ White NJ Swasdichai C Weatherall DJ The importance of anaemia in cerebral and uncomplicated falciparum malaria role of compli-cations dyserythropoiesis and iron sequestration Q J Med 198658305ndash23

31 Abdalla S Weatherall DJ Wickramasinghe SN Hughes M The anaemia of P falciparum malaria Br J Haematol 198046171ndash83

32 Sen R Bhatnagar BM Singh U Yadav MS Sehgal PK Patterns of erythropoiesis and anaemia in malaria J Commun Dis 199022247ndash53

33 Srichaikul T Wasanasomsithi M Poshyachinda V Panikbutr N Rabieb T Ferrokinetic studies and eryth-ropoiesis in malaria Arch Intern Med 1969124623ndash8

34 Das BS Thurnham DI Das DB Influence of malaria on markers of iron status in children implications for interpreting iron status in malaria-endemic communi-ties Br J Nutr 199778751ndash60

35 Menendez C Quinto LL Kahigwa E Alvarez L Fern-andez R Gimenez N Schellenberg D Aponte JJ Tanner M Alonso PL Effect of malaria on soluble transferrin receptor levels in Tanzanian infants Am J Trop Med Hyg 200165138ndash42

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S538 A M Prentice et al

36 Stoltzfus RJ Chwaya HM Montresor A Albonico M Savioli L Tielsch JM Malaria hookworms and recent fever are related to anemia and iron status indicators in 0- to 5-y old Zanzibari children and these relationships change with age J Nutr 20001301724ndash33

37 Stoltzfus RJ Chwaya HM Albonico M Schulze KJ Savioli L Tielsch JM Serum ferritin erythrocyte pro-toporphyrin and hemoglobin are valid indicators of iron status of school children in a malaria-holoendemic population J Nutr 1997127293ndash8

38 Massaga JJ Kitua AY Lemnge MM Akida JA Malle LN Ronn AM Theander TG Bygbjerg IC Effect of intermittent treatment with amodiaquine on anaemia and malarial fevers in infants in Tanzania a randomised placebo-controlled trial Lancet 20033611853ndash60

39 Verhoef H West CE Kraaijenhagen R Nzyuko SM King R Mbandi MM van Laatum S Hogervorst R Schep C Kok FJ Malarial anemia leads to adequately increased erythropoiesis in asymptomatic Kenyan children Blood 20021003489ndash94

40 Stoltzfus RJ Chway HM Montresor A Tielsch JM Jape JK Albonico M Savioli L Low dose daily iron supplementation improves iron status and appetite but not anemia whereas quarterly anthelminthic treatment improves growth appetite and anemia in Zanzibari preschool children J Nutr 2004134348ndash56

41 Kurtzhals JA Addae MM Akanmori BD Dunyo S Koram KA Appawu MA Nkrumah FK Hviid L Anae-mia caused by asymptomatic Plasmodium falciparum infection in semi-immune African schoolchildren Trans R Soc Trop Med Hyg 199993623ndash7

42 Loyevsky M John C Dickens B Hu V Miller JH Gordeuk VR Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators Mol Biochem Parasitol 199910143ndash59

43 Scholl PF Tripathi AK Sullivan DJ Bioavailable iron and heme metabolism in Plasmodium falciparum Curr Top Microbiol Immunol 2005295293ndash324

44 Darbari D Loyevsky M Gordeuk V Kark JA Castro O Rana S Apprey V Kurantsin-Mills J Fluorescence meas-urements of the labile iron pool of sickle erythrocytes Blood 2003102357ndash64

45 Ginsburg H Iron acquisition by Plasmodium spp Para-sitol Today 199915466

46 Atamna H Ginsburg H Heme degradation in the presence of glutathione A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells J Biol Chem 199527024876ndash83

47 Gabay T Ginsburg H Hemoglobin denaturation and iron release in acidified red blood cell lysatemdasha possible source of iron for intraerythrocytic malaria parasites Exp Parasitol 199377261ndash72

48 Iyer JK Shi L Shankar AH Sullivan DJ Jr Zinc pro-toporphyrin IX binds heme crystals to inhibit the proc-ess of crystallization in Plasmodium falciparum Mol Med 20039175ndash82

49 Cabantchik ZI Moody-Haupt S Gordeuk VR Iron che-lators as anti-infectives malaria as a paradigm FEMS Immunol Med Microbiol 199926289ndash98

50 Hershko C Control of disease by selective iron deple-tion a novel therapeutic strategy utilizing iron chelators Baillieres Clin Haematol 19947965ndash1000

51 Pradines B Tall A Ramiandrasoa F Spiegel A Sokhna C Fusai T Mosnier J Daries W Trape JF Kunesch G Parzy D Rogier C In vitro activity of iron-binding compounds against Senegalese isolates of Plasmodium falciparum J Antimicrob Chemother 2006571093ndash9

52 Meshnick SR Yang YZ Lima V Kuypers F Kam-chonwongpaisan S Yuthavong Y Iron-dependent free radical generation from the antimalarial agent artem-isinin (qinghaosu) Antimicrob Agents Chemother 1993371108ndash14

53 Golenser J Domb A Mordechai-Daniel T Leshem B Luty A Kremsner P Iron chelators correlation between effects on Plasmodium spp and immune functions J Parasitol 200692170ndash7

54 Nyakeriga AM Williams TN Marsh K Wambua S Perlmann H Perlmann P Grandien A Troye-Blomberg M Cytokine mRNA expression and iron status in chil-dren living in a malaria endemic area Scand J Immunol 200561370ndash5

55 Smith HJ Meremikwu M Iron chelating agents for treating malaria Cochrane Database Syst Rev 2003CD001474

56 Weatherall DJ The global problem of genetic disease Ann Hum Biol 200532117ndash22

57 Williams TN Maitland K Bennett S Ganczakowski M Peto TE Newbold CI Bowden DK Weatherall DJ Clegg JB High incidence of malaria in alpha-thalassaemic children Nature 1996383522ndash5

58 Rees DC Williams TN Maitland K Clegg JB Weather-all DJ Alpha thalassaemia is associated with increased soluble transferrin receptor levels Br J Haematol 1998103365ndash9

59 Maitland K Williams TN Bennett S Newbold CI Peto TE Viji J Timothy R Clegg JB Weatherall DJ Bowden DK The interaction between Plasmodium falciparum and P vivax in children on Espiritu Santo island Van-uatu Trans R Soc Trop Med Hyg 199690614ndash20

60 Weatherall DJ Clegg JB Genetic variability in response to infection malaria and after Genes Immun 2002 3331ndash7

61 Parikh S Dorsey G Rosenthal PJ Host polymorphisms and the incidence of malaria in Ugandan children Am J Trop Med Hyg 200471750ndash3

62 Destro Bisol G Genetic resistance to malaria oxidative stress and hemoglobin oxidation Parassitologia 1999 41203ndash4

63 Cappadoro M Giribaldi G OrsquoBrien E Turrini F Mannu F Ulliers D Simula G Luzzatto L Arese P Early phago-cytosis of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes parasitized by Plasmodium falciparum may explain malaria protection in G6PD deficiency Blood 1998922527ndash34

64 Arese P Turrini F Schwarzer E Band 3complement-mediated recognition and removal of normally senes-cent and pathological human erythrocytes Cell Physiol Biochem 200516133ndash46

65 Atkinson SH Rockett K Sirugo G Bejon PA Fulford A OrsquoConnell M A Bailey R Kwiatkowski DP Prentice AM Seasonal Childhood Anaemia in West Africa Is Associated with the Haptoglobin 2-2 Genotype PLoS Med 20063e172

66 Cabrera G Cot M Migot-Nabias F Kremsner PG Deloron P Luty AJ The sickle cell trait is associated

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S539Iron metabolism and malaria

with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens J Infect Dis 20051911631ndash8

67 Williams TN Mwangi TW Roberts DJ Alexander ND Weatherall DJ Wambua S Kortok M Snow RW Marsh K An immune basis for malaria protection by the sickle cell trait PLoS Med 20052e128

68 Ayi K Turrini F Piga A Arese P Enhanced phagocyto-sis of ring-parasitized mutant erythrocytes a common mechanism that may explain protection against falci-parum malaria in sickle trait and beta-thalassemia trait Blood 20041043364ndash71

69 Roberts DJ Harris T Williams T The influence of inherited traits on malaria infection In Bellamy R ed Susceptibility to infectious diseases the importance of host genetics Cambridge Cambridge University Press 2004 139ndash84

70 Williams TN Mwangi TW Wambua S Alexander ND Kortok M Snow RW Marsh K Sickle cell trait and the risk of Plasmodium falciparum malaria and other child-hood diseases J Infect Dis 2005192178ndash86

71 Aidoo M Terlouw DJ Kolczak MS McElroy PD ter Kuile FO Kariuki S Nahlen BL Lal AA Udhayakumar V Protective effects of the sickle cell gene against malaria morbidity and mortality Lancet 20023591311ndash2

72 Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K Nega-tive epistasis between the malaria-protective effects of alpha+-thalassemia and the sickle cell trait Nat Genet 2005371253ndash7

73 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S Ascaso C Smith T MrsquoBoge B Greenwood BM The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS Trans R Soc Trop Med Hyg 199589289ndash92

74 Terlouw DJ Desai MR Wannemuehler KA Kariuki SK Pfeiffer CM Kager PA Shi YP Ter Kuile FO Relation between the response to iron supplementation and sickle cell hemoglobin phenotype in preschool children in western Kenya Am J Clin Nutr 200479466ndash72

75 Duffy PE Fried M Malaria in the pregnant woman Curr Top Microbiol Immunol 2005295169ndash200

76 Schellenberg D Menendez C Kahigwa E Aponte J Vidal J Tanner M Mshinda H Alonso P Intermittent treatment for malaria and anaemia control at time of routine vaccinations in Tanzanian infants a randomised placebo-controlled trial Lancet 20013571471ndash7

77 Schellenberg D Menendez C Aponte JJ Kahigwa E Tanner M Mshinda H Alonso P Intermittent preventive antimalarial treatment for Tanzanian infants follow-up to age 2 years of a randomised placebo-controlled trial Lancet 20053651481ndash3

78 OrsquoMeara WP Breman JG McKenzie FE The promise and potential challenges of intermittent preventive treat-ment for malaria in infants (IPTi) Malar J 2005433

79 White NJ Intermittent presumptive treatment for malaria PLoS Med 20052e3

80 Elagib AA Kider AO Akerstrom B Elbashir MI Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan Trans R Soc Trop Med Hyg 199892309ndash11

81 Minang JT Gyan BA Anchang JK Troye-Blomberg M Perlmann H Achidi EA Haptoglobin phenotypes and malaria infection in pregnant women at delivery in western Cameroon Acta Trop 200490107ndash14

82 Quaye IK Ekuban FA Goka BQ Adabayeri V Kurtzhals JA Gyan B Ankrah NA Hviid L Akanmori BD Hap-toglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria Trans R Soc Trop Med Hyg 200094216ndash9

83 Singh IP Walter H Bhasin MK Bhardwaj V Sudhakar K Genetic markers and malaria Observations in Gujarat India Hum Hered 19863631ndash6

84 Aucan C Walley AJ Greenwood BM Hill AV Hap-toglobin genotypes are not associated with resistance to severe malaria in The Gambia Trans R Soc Trop Med Hyg 200296327ndash8

85 Bienzle U Eggelte TA Adjei LA Dietz E Ehrhardt S Cramer JP Otchwemah RN Mockenhaupt FP Limited influence of haptoglobin genotypes on severe malaria in Ghanaian children Trop Med Int Health 200510668ndash71

86 Takeda M Kikuchi M Ubalee R Na-Bangchang K Ruangweerayut R Shibahara S Imai S Hirayama K Microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with susceptibility to cerebral malaria in Myanmar Jpn J Infect Dis 2005 58268ndash71

87 Shankar AH Nutritional modulation of malaria mor-bidity and mortality J Infect Dis 2000182 Suppl 1 S37ndash53

88 Gera T Sachdev HP Effect of iron supplementation on incidence of infectious illness in children systematic review Bmj 20023251142

Page 3: Iron metabolism and malaria

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S526 A M Prentice et alTa

ble

2 P

ublis

hed

tria

ls of

ora

l iro

n su

pple

men

tatio

n an

d m

alar

ia ri

sk

Firs

t aut

hor

Sour

ce a

nd y

ear

Stud

y de

sign

Mal

aria

at b

asel

ine

Iron

stat

us in

clus

ion

crite

ria

Cas

e de

tect

ion

and

trea

tmen

t of m

alar

ia

inci

dent

cas

esFi

ndin

gs

Mur

ray

[10]

BMJ 1

978

11ndash6

0 yr

sin

gle-

blin

d RC

T ir

on (9

00 m

g fe

rrou

s sul

fate

) vs

plac

ebo

N =

137

Excl

uded

par

asite

mic

su

bjec

tsH

b lt

11A

ctiv

e ca

se d

etec

tion

no

dat

a on

trea

tmen

tIn

terv

entio

n gr

oup

had

incr

ease

d H

b (3

6 g

dL

) and

tr

ansf

errin

and

incr

ease

d cl

inic

al m

alar

ia at

tack

s (O

R =

147

9)

Har

vey

[26]

Am

J Tr

op M

ed H

yg

1989

8ndash12

yr

iron

(200

mg

ferr

ous s

ulfa

te) v

s pl

aceb

o N

= 3

18

70

par

asite

mic

at

base

line

Hb

8ndash12

gd

L A

ctiv

e m

orbi

dity

re

ferr

al to

hea

lth

faci

lity

Diff

eren

ces i

n m

alar

ia p

ara-

sitem

ia at

bas

elin

e be

twee

n pl

aceb

o an

d in

terv

entio

n

mak

e fin

ding

s diff

icul

t to

inte

rpre

t0

6 g

dL d

iffer

ence

in

Hb

betw

een

grou

psPe

rcen

tage

of c

hild

ren

with

pa

rasit

emia

dec

reas

ed in

bo

th g

roup

s Pe

rcen

tage

with

pa

rasit

emia

in ir

on g

roup

re

mai

ned

high

er th

an th

at in

pl

aceb

o gr

oup

Aut

hors

con-

clud

e th

at ir

on th

erap

y ha

s no

effe

ct o

n m

alar

ia

Smith

[11]

Ann

Tro

p Pa

edia

tr

1989

6 m

ondash5

yr i

ron

(3ndash

6mg

kg fe

rrou

s su

lfate

) vs

plac

ebo

N

= 2

13

Dat

a no

t ava

ilabl

eH

b 5ndash

11 g

dL

Act

ive

mor

bidi

ty

surv

ey b

ut li

mite

d ac

cess

to m

edic

al

faci

litie

s

Iron

supp

lem

enta

tion

incr

ease

d H

b M

CV

seru

m ir

on t

rans

-fe

rrin

satu

ratio

n se

rum

fer-

ritin

In

crea

sed

feve

r ass

ocia

ted

with

pa

rasit

emia

OR

= 6

47

Chi

ppau

x [1

5]Bu

ll So

c Pat

hol E

xot

1991

6ndash36

mo

iron

(25

m

gkg

ferr

ous s

ulfa

te)

vs p

lace

bo N

= 2

20

Appr

ox 6

0 p

ara-

sitem

ic at

bas

elin

eH

b ge

8 g

dLA

ctiv

e tr

eatm

ent o

f m

alar

ia in

cide

nt c

ases

OR

for m

alar

ia-p

ositi

ve sm

ear

= 1

28 (N

S)

Law

less

[20]

J Nut

r 199

46ndash

11 y

r iro

n (1

50 m

g fe

rrou

s sul

fate

) vs

plac

ebo

N =

87

Dat

a no

t ava

ilabl

e75

h

ad H

b lt

12 g

dL

at b

asel

ine

Dat

a no

t ava

ilabl

eIr

on su

pple

men

tatio

n in

crea

sed

seru

m fe

rriti

n by

16

5 microg

L

vs p

lace

bo

No

diffe

renc

es in

pre

vale

nce

of

mal

aria

afte

r sup

plem

enta

tion

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S527Iron metabolism and malariaM

enen

dez [

23]

Tran

s R S

oc T

rop

Med

H

yg 1

994

Mul

tigra

vid

preg

nant

w

omen

iro

n (2

00 m

g fe

rrou

s sul

fate

) vs

plac

ebo

N =

550

Dat

a no

t ava

ilabl

ePC

V gt

25

Mea

n H

b =

10g

dL at

ba

selin

e

Act

ive

trea

tmen

t of

mal

aria

inci

dent

cas

esD

ecre

ased

pre

vale

nce

of

anem

ia a

nd o

f iro

n de

fi-ci

ency

Ir

on su

pple

men

tatio

n w

as n

ot

signi

fican

tly a

ssoc

iate

d w

ith

susc

eptib

ility

to p

reva

lenc

e or

se

verit

y of

mal

aria

van

Hen

sbro

ek [2

4]Tr

ans R

Soc

Tro

p M

ed

Hyg

199

56

mondash

9 yr

chl

oro-

quin

e vs

SP

+ ra

n-do

miz

atio

n to

iron

(asymp

100

mg

elem

enta

l iro

n) v

s fo

late

vs

pla-

cebo

N =

530

All

child

ren

wer

e re

crui

ted

at cl

inic

w

ith u

ncom

plic

ated

m

alar

ia

74

had

Hb

lt 11

g

dL at

bas

elin

eA

ll ch

ildre

n re

ceiv

ed

trea

tmen

t for

mal

aria

as

par

t of t

he tr

ial

Iron

gro

up h

ad m

ean

incr

ease

in

Hb

= 0

81 g

dL

Fola

te su

pple

men

tatio

n di

d no

t im

prov

e he

mat

olog

ical

pa

ram

eter

s and

incr

ease

d ra

te

of tr

eatm

ent f

ailu

re in

chil-

dren

rece

ivin

g SP

Ir

on d

id n

ot a

ffect

susc

eptib

il-ity

to m

alar

ia

Nw

anya

nwu

[17]

Ann

Tro

p M

ed P

aras

i-to

l 199

6lt

5 yr

SP

vs S

P +

daily

iron

(25

mg

kg fe

rrou

s sul

fate

) vs

SP

+ w

eekl

y iro

n

N

= 2

22

Incl

usio

n cr

iterio

n

para

site

dens

itygt

500

microl w

hole

blo

od

Hb

ge 5

gdL

All

wer

e tr

eate

d w

ith

SPD

aily

iron

+ S

P H

b in

crea

sed

49

gdL

vs

35ndash

37

gdL

in

SP a

nd S

P +

wee

kly

iron

G

reat

est b

enef

it on

Hb

in H

b gr

oup

5ndash8

gdL

at b

asel

ine

Iron

gro

ups h

ad in

crea

sed

trea

tmen

t fai

lure

vs

SP a

lone

(N

S)

van

den

Hom

berg

h [1

9]

J Tro

p Pe

diat

r 199

6lt

30 m

o ir

on (2

00

mg

ferr

ous s

ulfa

te) +

fo

late

vs

fola

te o

nly

N =

100

Onl

y in

clud

ed ch

il-dr

en w

ith p

aras

ite-

posit

ive

thic

k fil

ms

Hb

le 5

gdL

All

rece

ived

trea

tmen

t w

ith S

P +

quin

ine

40

rece

ived

blo

od tr

ans-

fusio

n

Diff

eren

ces i

n ba

selin

e ch

arac

-te

ristic

s (H

b p

aras

ite d

ensit

y be

twee

n gr

oups

)N

o sig

nific

ant d

iffer

ence

in

chan

ge in

Hb

betw

een

grou

psN

o di

ffere

nces

in m

alar

ia in

di-

ces b

etw

een

grou

ps

Men

ende

z [22

] La

ncet

199

72ndash

12 m

o ir

on (2

mg

kg fe

rrou

s gly

cine

sul-

fate

) + D

elta

prim

vs

iron

vs D

elta

prim

vs

plac

ebo

N =

832

24

of c

hild

ren

wer

e pa

rasit

emic

at b

ase-

line

PCV

gt 2

5Pa

ssiv

e ca

se d

etec

tion

plus

hig

h us

e of h

ealth

se

rvic

es

Iron

supp

lem

enta

tion

decr

ease

d an

emia

by

288

and

mal

aria

chem

opro

phy-

laxi

s dec

reas

ed a

nem

ia b

y 60

5

Iron

supp

lem

enta

tion

had

no

effe

ct o

n fr

eque

ncy

of m

alar

iaco

ntin

ued

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S528 A M Prentice et al

Berg

er [

14]

Eur J

Clin

Nut

r 200

06ndash

36 m

o iro

n (2

ndash3

mg

kg ir

on b

atai

n-at

e) v

s pl

aceb

o

N

= 1

97

62

of c

hild

ren

wer

e pa

rasit

emic

at

base

line

Hb

ge 8g

dL

Act

ive

mor

bidi

ty

follo

w-u

p an

d tr

eat-

men

t of a

ll fe

vers

w

ith a

ntim

alar

ials

Prev

alen

ce o

f iro

n-de

ficie

ncy

anem

ia d

ecre

ased

in ir

on

grou

p an

d in

crea

sed

in p

la-

cebo

gro

upA

ll m

arke

rs o

f iro

n st

atus

wer

e sig

nific

antly

hig

her i

n iro

n gr

oup

Incr

ease

in p

erce

ntag

e of

chil-

dren

with

par

asite

mia

gt 3

000

in

iron

gro

up (N

S)

Verh

oef [

18]

Lanc

et 2

002

2ndash36

mo

iron

(6 m

gkg

wk

ferr

ous f

uma-

rate

) vs

SP v

s iro

n +

SP v

s pl

aceb

o

N

= 3

28

Onl

y as

ympt

omat

ic

mal

aria

incl

uded

(3

0 d

ipst

ick

posi-

tive

at b

asel

ine)

Hb

6ndash11

gd

L A

ctiv

e fo

llow

-up

of

feve

rs a

nd tr

eatm

ent

upon

dia

gnos

is

SP a

lone

incr

ease

d H

b by

03

1 g

dLIr

on +

SP

incr

ease

d H

b by

11

1 g

dLIr

on a

lone

incr

ease

d H

b by

10

7 g

dLIn

crea

se in

mal

aria

risk

with

iro

n su

pple

men

tatio

n (N

S)

Des

ai [1

6]J I

nfec

t Dis

2003

2ndash36

mo

IPT

+ iro

n (3

ndash6 m

gkg

ferr

ous

sulfa

te) v

s iro

n vs

IP

T vs

pla

cebo

N

= 5

46

26

of c

hild

ren

wer

e pa

rasit

emic

at b

ase-

line

(are

a of

hig

h IT

N u

se

Hb

7ndash10

9 g

dL

Pass

ive

surv

eil-

lanc

e sy

stem

and

ac

tive

trea

tmen

t of

mal

aria

and

ane

mia

(4

-wee

kly

visit

s)

Iron

gro

up h

ad m

ean

incr

ease

in

Hb

of 0

88g

dL

Ir

on +

IPT

mea

n in

crea

se in

H

b =

114

gd

LIn

crea

se in

mal

aria

par

asite

mia

(N

S) H

R =

114

N

o ef

fect

on

HR

of cl

inic

al

mal

aria

Meb

raht

u [2

1]J N

utr 2

004

4ndash71

mo

iron

(10

mg

ferr

ous s

ulfa

te) v

s iro

n +

meb

enda

zole

vs

meb

enda

zole

+

plac

ebo

vs p

lace

bo

supp

lem

ente

d fo

r 12

mo

N =

614

84

of c

hild

ren

wer

e pa

rasit

emic

at

base

line

94

had

Hb

lt 11

gd

LA

ctiv

e su

rvei

llanc

e no

trea

tmen

tIn

crea

sed

seru

m fe

rriti

nD

ecre

ased

zinc

pro

topo

rphy

rin

in su

pplem

ente

d gr

oup

N

o di

ffere

nce

in m

alar

iom

etric

in

dice

s (pr

eval

ence

or p

ara-

sitem

ia)

but c

linic

al v

alue

s no

t ass

esse

d

Tabl

e 2

Pub

lishe

d tr

ials

of o

ral i

ron

supp

lem

enta

tion

and

mal

aria

risk

Firs

t aut

hor

Sour

ce a

nd y

ear

Stud

y de

sign

Mal

aria

at b

asel

ine

Iron

stat

us in

clus

ion

crite

ria

Cas

e de

tect

ion

and

trea

tmen

t of m

alar

ia

inci

dent

cas

esFi

ndin

gs

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S529Iron metabolism and malaria

partly explain the variations in response to iron supple-mentation reported by different studies other potential complicating factors that contribute to these variations are described in table 4

All but two studies [15 19] have found significant positive effects on markers of iron status in those receiving iron supplementation In the trial of van den Hombergh et al [19] the sample size was limited and baseline characteristics were significantly different between the supplementation and placebo groups Chippaux et al [15] found that anemic children who remained parasite free had increased hemoglobin levels postsupplementation but those that subsequently developed malaria did not The effect of supplementa-tion on hemoglobin concentrations ranged between 06 and 49 gdL with the highest increase occurring in a study that combined iron supplements with anti-malarial therapy [17] Other studies have also shown an additional advantage of iron plus antimalarials as regards hemoglobin recovery [16 18] However despite the hematological benefits all of these studies found nonsignificant increases in adverse malarial outcomes in the groups that received antimalarials plus iron including increased parasite density [16] risk of malaria [18] and treatment failure [17]

Six studies found no effect of iron supplements on malaria risk [19ndash24] of these three included large proportions of anemic subjects (74 to 94) [20 21 24] and one included only children with hemoglobin lt 5 gdL [19] Other studies that stratified by baseline hemoglobin levels [17 25] found that the greatest ben-efits occurred in the most anemic subgroups

Three studies found an increase in clinical malaria attacks in the iron-supplemented groups [10 11 25] and a further six studies found nonsignificant increases in malaria outcomes [14ndash18 26] One of the striking differences between study populations with significant increases in malaria outcomes and those with non-significant effects is access to health care and active treatment of malaria incident cases In fact all but one of the trials [21] that found no effect on malaria outcomes provided access to health care facilities or active follow-up and treatment of malaria incident cases This implies that the potential detrimental effects of iron supplementation may be curtailed by concurrent effective treatment of malaria infections However Verhoef et al and Nwanyanwu et al have shown potential treatment failure effects of combining sulfadoxinendashpyrimethamine with iron in the treatment of preexisting malaria suggesting that antimalarial therapy should precede supplementation [2 17 18]

These observations are further confirmed by a large study in Zanzibar by Sazawal et al [25] that showed increases in malaria-related morbidity and mortality in the iron-supplemented arms of a randomized control-led trial of ironfolate and ironfolate plus zinc versus placebo (summarized in table 2) A subgroup of this Sa

zaw

al[2

5]La

ncet

200

61ndash

35 m

o ir

on (1

25

mg)

+ fo

late

vs

iron

+ fo

late

+ zi

nc v

s pl

aceb

o m

orbi

d-ity

and

mor

talit

y ou

tcom

es a

sses

sed

N

= 3

215

5

43

wer

e pa

rasit

emic

at

bas

elin

eH

b gt

7 g

dL 5

7 o

f ch

ildre

n ha

d H

b lt

10 g

dL

at b

asel

ine

Trea

ted

subs

tudy

chil-

dren

with

clin

ical

m

alar

ia w

ith S

P at

ba

selin

e 6

mo

and

12

mo

Com

bine

d iro

n gr

oups

vs

pla-

cebo

Fo

r adv

erse

mal

aria

-rel

ated

ev

ents

RR

= 1

16

For c

ereb

ral m

alar

ia R

R =

122

Iron

+ fo

late

vs

plac

ebo

For c

ereb

ral m

alar

ia a

s a c

ause

of

dea

th R

R =

17

Subs

tudy

Lo

wer

rate

of a

dver

se e

vent

s in

child

ren

iron

defic

ient

at

base

line

Prot

ectiv

e ef

fect

of i

ron

+ fo

late

in

iron

-def

icie

nt a

nem

ic ch

il-dr

en R

R =

051

Sig

nific

ant d

iffer

ence

s as

repo

rted

by

the

auth

ors

RCT

ran

dom

ized

con

trol

led

tria

l H

b h

emog

lobi

n O

R o

dds

ratio

MC

V m

ean

corp

uscu

lar

volu

me

NS

not

sig

nific

ant

PCV

pac

ked

cell

volu

me

SP

sul

fado

xine

ndashpyr

imet

ham

ine

IPT

inte

rmitt

ent

prev

entiv

e th

erap

y IT

N i

nsec

ticid

e tr

eate

d be

dnet

s ]H

R h

azar

d ra

tio R

R re

lativ

e ris

k

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S530 A M Prentice et al

trial was investigated in more detail and consequently received more intensive diagnosis and treatment of malaria and other infections Substudy children with iron-deficiency anemia at baseline benefited sig-nificantly from iron supplementation in that they had reduced malaria and other infection-related hospital admissions and mortality [25]

The results of this recent study in Zanzibari children have raised new concerns about possible serious side effects of iron supplementation in populations where the etiology of anemia is not solely attributable to iron

deficiency and point to the need for a deeper under-standing of the complex biology of iron sequestration and redistribution between different storage and functional compartments and of the underlying host factors that influence these processes

Effect of malaria on iron metabolism

Erythropoietic iron requirement is met largely through recycling of senescent red blood cells through reticu-loendothelial macrophages where iron is repackaged onto transferrin for transport to the bone marrow [27] Red blood cells are predominantly engulfed directly by reticuloendothelial macrophages however up to 10 of normal recycling occurs as a result of intravascular hemolysis Hemoglobin is released and rapidly bound to haptoglobin and the resultant complex is cleared by liver parenchymal cells or the CD163 macrophagal receptor [28] Malaria-induced destruction of infected and noninfected red blood cells both stresses and impedes the capacity of reticuloendothelial macro-phages to recycle iron back to the bone marrow Intra-vascular rupture of parasitized red cells macrophagal phagocytosis of both parasitized and unparasitized red cells and hypersplenism all contribute to the patho-physiology of the anemia associated particularly with acute malaria

The local epidemiology and transmission character-istics of Plasmodium falciparum together with local drug treatment and intermittent preventive therapy

TABLE 3 Meta-analyses and reviews

First author Sourceyear Study design Findings

Shankar [87] J Infect Dis 2000 Meta-analysis of 13 RCTs of the effect of iron supplementation on malaria and iron status

RR for clinical malaria attack = 11 (NS)RR for slide positive for Plasmodium falci-

parum = 117Absolute increase in infection rate = 57 (NS)RR for spleen enlargement = 112 (NS)Mean increase in Hb = 125 gdLRR for anemia = 05

Oppenheimer [2] J Nutr 2001 Review of controlled interven-tion studies of iron supplemen-tation

Oral iron therapy increased clinical malaria in 5 out of 9 studies

No studies of iron therapy in malarious areas showed benefits on infectious morbidity

Does not report on effect on iron status

Gera [88] BMJ 2002 Systematic review of 28 RCTs of the effect of iron supplementa-tion or fortification in children on infectious illness (including 8 studies of the effect of iron supplementation on malaria)

Pooled OR for malaria-positive smear = 143 but OR when adjusted for baseline malaria smear = 124 (NS)

(The treatment effect increased by 289 times per unit increase in baseline malaria posi-tivity this supports the argument that iron supplementation of children with preexist-ing malaria increases their risk of remaining malaria positive)

Significant differences as reported by the authors RCT randomized controlled trial RR relative risk NS not significant Hb hemoglobin OR odds ratio

TABLE 4 Factors complicating assessment of the relationship between iron status and malaria and the response to iron sup-plementation in malaria-endemic populations

raquo Differences in dose duration and route of iron admin-istration

raquo Degree of malaria immunity in study individuals which can also be related to age and local malaria transmission patterns [7]

raquo Supplementation with iron and folate vs iron alone (especially as some antimalarials have antifolate action) [24]

raquo Markers of iron status used (the confounding effect of infection on serum markers of iron deficiency) [2 8]

raquo Baseline iron status iron-deficient individuals benefit [18 21]

raquo Access to health care and intensity of malaria surveil-lance and treatment during the trial [18 25]

raquo Hemoglobinopathies may affect anemia and response to iron supplementation as well as risk of malaria [9 73]

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S531Iron metabolism and malaria

(IPT) practices influence population immunity and resultant malarial clinical presentation as well as the epidemiology of anemia in a particular setting These factors may also influence the disturbance of iron metabolism and erythropoietic response to iron sup-plementation Acute malaria is associated predomi-nantly with a picture of fever hemolysis and oxidant stress whereas dyserythropoiesis predominates in the anemia of chronic malaria in a semiimmune patient [29] Acute malarial hemolysis represents a major stress on the homeostatic mechanisms of iron flux regulation that have evolved primarily to maintain erythroblast supply while minimizing the oxidant stress-associated effects of iron

Iron can be sequestered and trapped in reticuloen-dothelial macrophages as a result of both chronic and acute malaria and can present a picture of iron-deficient erythropoiesis associated with normal or increased bone marrow iron For instance bone marrow aspirates in 23 Thai patients with uncomplicated acute malaria (age 15 to 52 years) demonstrated malarial pigment in 22 of them Convalescent bone marrow aspirates in 16 patients (3 to 25 days after admission) demonstrated increased iron content compared with the admission sample [30] Five of six Gambian children (lt 5 years of age) with acute malaria had elevated stainable bone marrow iron and four of six children with chronic malaria and severe anemia (hemoglobin lt 6 gdL) had either normal or markedly increased levels of bone marrow stainable iron [31] Eighty-six percent of Indian children and adults (N = 26) with acute and 84 of those with chronic falciparum malaria and anemia (mean hemoglobin 54 gdL N = 38) had normal or increased bone marrow iron stores [32] Ferrokinetic studies involving the intravenous administration of 59Fe demonstrated low unsaturated iron-binding capacity and a rapid plasma iron disappearance time in both parasitemic and postparasitemic patients with acute and secondary (recent acute infection with persistent parasitemia) P falciparum and P vivax in Thai adults compared with controls [33] Incorporation of 59Fe into red blood cells was decreased in acute (N = 5) and secondary parasitemia (11 of 14) but found to be largely normal in the postparasitemic patients includ-ing 3 who were restudied from the parasitemic group Iron sequestration in acute malaria is cytokine driven (elevated tumor necrosis factor α [TNF-α] ILndash1 and interferon γ [IFN-γ] and diminished ILndash10) [29] prob-ably mediated via hepcidin however quantifying this phenomenon assessing how long it persists after acute malaria and in association with chronic malaria and assessing its importance in relation to malarial anemia malaria-associated immunosuppression and response to iron supplementation is difficult since there are few data Conventional indices of iron storage (eg ferritin) or of tissue supply (eg zinc protoporphyrin soluble transferrin receptor transferrin saturation) are

affected by inflammation [8 34ndash36] and the assess-ment of the iron status of young children in malarious areas with acute or chronic malaria is problematic [34] In a holoendemic environment ferritin and eryth-rocyte protoporphyrin were not affected by chronic malaria in older children [37] These indices also do not distinguish between iron deficiency and iron sequestration

Effect of malaria on response to iron supplementation

Malaria-induced anemia does not lead to loss of iron from the body However iron deficiency often coex-ists with malaria in areas of malaria transmission and therapy for severe postmalarial anemia commonly assumes a component due to preexisting iron defi-ciency Iron supplements are routinely prescribed both for severe malaria-associated anemia and for presumed iron-deficient anemia in a malaria-endemic environ-ment Few studies however have looked at the effect of acute malaria on the response to iron supplementation and even fewer have addressed the effect of chronic asymptomatic malaria More commonly studies either have either assessed the response to supplementation of children with anemia of undefined etiology in areas of coexistent malaria iron deficiency and hookworm or have randomized children who were anemic after malaria to a variety of hematinics In a study of 222 Malawian children (lt 5 years of age) with anemia after acute malaria the use of Fansidar and daily supplemen-tal iron resulted in a significantly greater hemoglobin recovery than Fansidar alone or Fansidar and weekly iron only in those children with initial hemoglobin between 5 and 8 gdL [17] However a larger propor-tion of the iron-treated children failed to clear their malaria In the Gambia 600 children (mean age 52 months mean hemoglobin 96 gdL) with uncompli-cated falciparum malaria randomized to receive chlo-roquine or Fansidar as treatment and then either iron folic acid or placebo for 28 days [22] demonstrated a significantly better hemoglobin response with iron than with placebo or folic acid (the difference in mean hemoglobin level after 1 month was 07 gdL) One hundred Tanzanian children (lt 30 months of age) with severe anemia (hemoglobin lt 5 gdL) were randomized either to receive daily iron supplementation or to be controls after antimalarial treatment [19] Among the 60 who completed the 12-week follow-up without a transfusion (30 in each group) there were no differ-ences in hemoglobin recovery From these studies the role of iron supplementation in the treatment of anemia after acute malaria is unclear and it is likely that the hemoglobin response to supplementation is influenced by both the direct inflammatory effect of malaria on iron absorption and utilization and preexistent iron

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S532 A M Prentice et al

deficiency which is impossible to assess in the presence of malaria In the Gambia we recently compared the absorption of stable-isotope-labeled iron in children anemic as a result of iron deficiency and children anemic after acute malaria Both groups were given 30 days of iron supplementation and the malaria group demonstrated significantly better hemoglobin recovery despite initially significantly reduced iron absorption (Doherty et al unpublished results) Utilization of sequestered iron is likely to be a major contributor to erythroblastic iron requirement after acute malaria

Studies of iron supplementation of populations of anemic children in malarious areas have reported either improved hemoglobin response or decreased prevalence of severe anemia [16 22 38 39] Incorpo-ration of antimalarial intervention arms is common Malaria transmission characteristics study design use of antecedent antimalarials differing iron supplemen-tation doses and differing outcome measures as well as different prevalence rates of iron deficiency and hook-worm infection have made the assessment of factors affecting hemoglobin response to iron supplementation difficult In particular the effect of chronic malaria on response to supplementation in high-transmission areas is unclear as the etiology of the anemia and the chronicity of malaria parasitemia are often undefined in study subjects In an area of intense transmission in Tanzania in which more than 80 of children (4 to 71 months old) were parasitemic at baseline and where malaria infection was strongly associated with hemo-globin supplementation improved the iron status and motor and language development of an iron-deficient population but not did not improve hemoglobin [21 36 40] The authors concluded that factors including malarial parasitemia or ineffective erythropoiesis due to inflammatory processes in a population with high levels of infectious morbidity and inflammation might have limited erythropoiesis

An inflammatory-mediated block to iron absorp-tion and utilization is likely to limit the erythropoietic response to supplemental iron after acute malaria how-ever it is unclear whether chronic parasitemia similarly limits the response to supplemental iron The asso-ciation of chronic malaria with anemia [39] stainable bone marrow iron [34] and increased cytokine levels [41] might suggest a probable effect and the eradica-tion of parasites has been associated with hemoglobin improvement without supplemental iron [31]

Iron metabolism by malaria parasites

In this section we consider whether the availability of iron in the host could modulate the efficiency with which malaria parasites can establish an infection and the severity of that infection What evidence is there to support the ldquonutritional immunityrdquo hypothesis that

host iron availability could limit parasite invasion or multiplication andor the clinical sequelae of para-site infection Support for the nutritional immunity hypothesis first stated in the 1970s has generally waned for the majority of pathogens [2] but there may still be a case for obligate intracellular pathogensmdashincluding Plasmodium spp

It may be informative to examine the research of other scientists than those typically involved in the cur-rent debate For example in order for this hypothesis to be truemdashat least in terms of the success of parasite invasion and replicationmdashit is a requirement that P falciparum be dependent on host iron sources for its survival Next is iron deficiency ever likely to be a limiting factor in the supply of iron to the parasite The most recent research suggests that P falciparum does utilize iron from the host but not from the abundant supplies available in erythrocyte hemoglobin the heme portion of which is quickly degraded to nontoxic but non-iron-bioavailable hemozoin or from the plasma via transferrin but from another source possibly an intraerythrocytic labile pool of ferrous iron [42 43] Interestingly measurements of this labile ferrous iron in normal and sickled erythrocytes indicate it to be positively associated with hemoglobin concentrations and negatively associated with plasma ferritin [44] However other researchers have reported evidence to suggest that the degradation of heme to hemozoin is incomplete and that 50 of heme may be degraded via an alternative pathway involving reduced glutathione and releasing bioavailable iron [45 46] As it has been estimated that less than 1 of heme iron would be sufficient to meet parasite iron requirements [47] iron deficiency would never induce iron-limited growth if hemoglobin were the iron source for parasites

Another mechanism by which iron deficiency may limit parasite growth is that proposed recently by Iyer et al [48] who demonstrated the inhibition of hemozoin formation from toxic free heme by the naturally occur-ring zinc protoporphyrin IX (ZPP) at levels likely to be encountered in anemic erythrocytes It is interesting to note that this is thought to be the mechanism by which the quinoline antimalarials act Furthermore Iyer et al demonstrated that quinolines competed for ZPP bind-ing and prevention of hemozoin formation It is pos-sible that via this mechanism moderate anemia could allow the persistence of low levels of parasitemia and therefore affect the development of exposure-related antibody repertoire and clinical immunitymdashwith consequent effects on future malarial incidence and malaria-associated anemia However the evidence for such an effect in human populations is currently limited due to the lack of longitudinal studies assessing ZPP levels and parasite prevalence and density from infancy onwards

Another research area that has been used to support the hypothesis of decreased iron availability is that

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S533Iron metabolism and malaria

of the effects of iron chelators on parasite growth in vitro and in vivo [49 50] Furthermore some antima-larial drugs such as the antibiotic cyclines including doxycycline are also iron chelators However iron chelators may not be acting by depriving the parasite of iron Alternative mechanisms have been suggested for some chelators including the induction of reactive oxygen species from dissociation of iron from heme and hemozoin as suggested for the lipophilic FR160 [51] similar to the suggested mechanism of artemisinin [52] Furthermore differences between the efficacy of chelators in vitro and in vivo have been associated with differences in immune modulation [53] This may suggest that iron status could affect malarial outcomes via direct effects on immune modulation as suggested by Nyakeriga et al [54] The evidence base for the effects of current iron-chelator therapies in reducing the prevalence density or clinical sequelae of malaria is weakmdashas outlined in a recent Cochrane review of clinical trials involving the use of either desferioxamine or the orally available deferiprone [55] in which all of the seven studies included had limitations relat-ing to study size relevance of study populations and more critically methodological and analytical faults However the authors of this review concluded that the results suggested possible benefits of treatment in cerebral malaria with a shorter recovery time from coma and decreased time to parasite clearance The initial justification for using iron-chelator therapy in cerebral malaria was based on the premise of prevent-ing iron-induced damage to brain cells resulting from hemolysis Therefore it is important to note that the possible benefits of iron-chelator therapy may not relate to limitation of iron for parasite growth and may there-fore not provide evidence in support of the nutritional immunity hypothesis

Iron malaria and hemoglobinopathies

How do hemoglobinopathies protect against parasite invasion or multiplication andor clinical sequelae of parasite infection Are these polymorphisms likely to affect the relationship between iron status or supple-mentation and malaria

J B S Haldane is credited with first postulat-ing heterozygote selection as an explanation for the high prevalence of the thalassemias and later other hemoglobinopathies He suggested that the small size reduced hemoglobin concentrations and increased resistance to hypertonic solutions of such cells may result in decreased parasite invasion or growth Although this hypothesis has been widely accepted for some time it has only recently been possible to dem-onstrate that these mutations have been maintained by selection mostly by malaria but possibly also other infectious causes However the extent and mechanisms

of protection are still debated At least in vitro many studies have failed to demonstrate decreased ability of parasites to invade or grow in thalassemic cells or cells containing hemoglobin S (HbS) Instead the mecha-nisms appear to be more complicated and possibly to vary between local conditions

The common polymorphisms involved in hemo-globin synthesis or red cell formation include sickle hemoglobin (HbS) HbC and HbE the α and β-thalassemias and South Asian ovalocytosis The geographic distribution of these varies across tropi-cal areas and can vary extensively even within closely related regions Current estimates of these polymor-phisms are often based on single sites and are likely to be underestimates [56] but a figure of 27 million carriers of the main hemoglobinopathies has been proposed [56] The carrier frequency for HbS is esti-mated at between 5 and 40 in populations across sub-Saharan Africa the Middle East and parts of South Asia HbC is limited to parts of West and North Africa whereas HbE is common in some parts of India and Southeast Asia with carrier rates up to 60 The thalassemias have the broadest geographic distribution and also the widest range of causative mutations and clinical outcomes The carrier frequencies for the more severe range of β-thalassemias is generally lower than for the α-thalassemias which are estimated to reach carrier frequencies of up to 20 in sub-Saharan Africa higher in Middle Eastern and Indian populations and up to 80 in some Pacific populations (reviewed in Williams et al [57] Rees et al [58] and Maitland et al [59])

In β-thalassemias excess α-globin chains precipitate in red cell precursors leading to ineffective erythropoi-esis and resulting in anemia in the context of increased iron absorption and iron accumulation The clinical expression of β-thalassemia varies widely depending on the exact genetic lesions inherited and interactions with other genetic loci including the α and γ globin genes β-Thalassemia trait and β-thalassemia interme-diate are often asymptomatic and may not be diagnosed except for mild anemia In α-thalassemia the excess β-chains form stable homotetramers which do not sig-nificantly affect erythropoiesis but cause an increased rate of hemolysis of mature cells The degree of the deficit of α-globin chains depends on the number of α-globin genes inactivated and unless three α-globin genes are lost the effects are subtle and various so that the condition will go largely undiagnosed It might be supposed that iron supplementation could be more deleterious in populations with a high prevalence of β-thalassemia mutations because of the inability to utilize the iron leading to increased iron availability to pathogens or iron-induced oxidant stress Interest-ingly Oppenheimer [2] reported that the increased susceptibility to malaria associated with parenteral iron in Papua New Guinean children was not apparent in

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S534 A M Prentice et al

single-deletion α-thalassemia compared with normal children

In a prospective casendashcontrol study in Papua New Guinea α-thalassemic α+ndash homozygotes and α+ndash heterozygotes had a greatly decreased risk of severe malaria (incidence rate ratio = 04 and 066) compared with controls [9] Furthermore protection was also observed for hospitalization from other infections possibly suggesting an immune component to the pro-tection [60] although the reduction of severe malaria may reduce infectious sequelae by invasive bacte-rial disease In apparent contrast α-thalassemia has also been associated with an increased prevalence of uncomplicated malaria in Vanuatu particularly in very young children with P vivax [57] It was suggested that increased red cell turnover in these children increased susceptibility to P vivax [58] resulting in cross-species immunity to P falciparum in later life [59] A similar finding was reported for glucose-6-phosphate dehy-drogenase (G6PD) deficiency in a cohort study in Uganda in which many other potential risk factors for malarial infection were controlled for (age water source use of prophylaxis bednet usage and proxim-ity to mosquito breeding sites) Female heterozygotes for G6PD had a significantly increased incidence of uncomplicated malaria (IRR = 13 p = 03) and a trend for increased parasite densities similar trends were seen for hemizygote males This was different from the pattern observed for HbS heterozygotes who had a nonsignificantly decreased incidence of uncomplicated malaria and decreased parasite densities [61]

A mechanism that has been suggested for G6PD defi-ciency and that may also be applicable to sickle (HbAS) and thalassemic cells involves decreased oxidative protection (G6PD) or increased constitutive oxidative stress of these cells (HbAS αβ thalassemias) especially when infected resulting in increased clearance of the cells from non-malaria-specific immune mechanisms essentially the same as the normal removal of old ldquosenescentrdquo red cells by phagocytes [62ndash64] It has been proposed that such a mechanism could prevent parasitemias from reaching critically high densities and therefore protect from severe malaria and also facilitate the development of antibody repertoires in children from the maintenance of low-grade infections in young children [65ndash67] In a slight modification of this hypothesis the increased phagocytic removal of early ring-stage infected cellsmdashcompared with schizonts and trophozoitesmdashhas been demonstrated for G6PD β-thalassemic and HbAS cells in vitro but not for α-thalassemic infected cells [68] The phagocytosis of ring compared with later stages may be advantageous since rings contain less hemozoin the buildup of which in monocytes has been associated with decreased func-tion Additionally the reduction of the later stages of parasite development may reduce the development of severe symptoms such as cerebral malaria from

reduced endothelial adhesion of late-stage infected red blood cells to receptors such as intracellular adhesion molecule-1 (ICAM-1)

The epidemiological evidence for a protective effect of HbAS suggests that the protective effects are great-est for severe disease (reviewed by Roberts et al [69]) In the most comprehensive study to date a detailed prospective cohort in two Kenyan populations it was reported that HbS heterozygotes had a significantly decreased risk of mild clinical malaria as assessed by active surveillance (50 decreased risk 95 confi-dence interval [CI] 26 to 67]) a 75 (95 CI 84 to 61) decreased risk of hospital admission for malaria and a 90 [95 CI 3 to 99] decreased risk of severe malaria (severe malarial anemia cerebral malaria or complicated malaria) [70] There was no effect of HbAS on the risk of asymptomatic infec-tions or of parasite density in asymptomatic infections assessed at four cross-sectional surveys There were significant decreases in parasite densities for all of the other categories of infection Additionally in this study unlike another in western Kenya [71] the protection was specific to malaria and did not extend to other common childhood infections including respiratory infections gastroenteritis and helminth infections

What influence the hemoglobinopathic and other polymorphisms may have on the effect of iron sup-plementation on malarial susceptibility is potentially dependent on the extent and mechanisms of protection from infection in the different genotypesmdashinfluences that are likely to be further complicated by differential effects according to age and malarial exposure and effects of coinheritance [72] The coinheritance of the HbS G6PD deficiency and α-thalassemia deletion alle-les is likely to be prevalent in sub-Saharan populations making the study of such effects in real populations extremely difficult by requiring very large sample sizes and complex statistical modeling

To the authorsrsquo knowledge only two published randomized controlled trials of iron supplementation have assessed the effects by genotypemdashin both cases by HbAS versus HbAA [73 74]

In the first trial involving Traditional Birth Attend-ant-administered routine iron supplementation to multigravid Gambian pregnant women Menendez et al [73] reported that although overall there were significant beneficial effects on hemoglobin and packed cell volume (PCV) and on birthweight these effects were entirely accounted for by women with the HbAA phenotype (N = 402 vs N = 98) whereas iron-supplemented HbAS women had lower HB PCV and birthweight than HbAA women receiving placebo Furthermore even in this relatively small study these interactions were statistically significant (p lt 01 for hematological indices at delivery baseline measurements as a covariate p lt 03 for birthweight maternal height included as a covariate) Overall

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S535Iron metabolism and malaria

there was no reported increase in susceptibility to malaria as assessed by the prevalence of peripheral malaria at late pregnancy and delivery or by placental histology Yet iron-supplemented HbAS women had an increased prevalence of placental malaria (76 [2229]) compared with iron-supplemented HbAA women (53 [83158]) placebo-treated HbAA women (59 [91154]) or placebo-treated HbAS women (58 [1933]) At the time of this study IPT prophylaxis was recommended only for primigravid pregnant women in the Gambia hence the choice of the study population What the effects of iron supplementation might be in either primigravidae or multigravidae receiving IPTmdashwhich is now recommended for all pregnant women in malaria-endemic countriesmdashhas not been assessed The protection afforded by the HbAS genotype is likely to vary according to gravidity and malarial endemic-ity In areas of high transmission the majority of the increased risk is borne by primigravidae whereas in areas of lower and highly defined seasonal transmis-sion the increased risk extends to a greater number of pregnancies [75] The protective effect of HbAS is thought to be greatest in relatively nonimmune young children who have not yet developed acquired immunity by exposure to a variety of clonal variants of P falciparum and therefore have not developed a full antibody repertoire to the variant surface antigens (VSA) expressed on the cell surfaces of parasitized red blood cells

In the second trial the effect of the HbAS phenotype on the response to iron supplementation in children was assessed in a subanalysis of a 2 times 2 randomized controlled trial of iron supplementation and inter-mittent preventive treatment (IPT) for malaria using sulfadoxinendashpyrimethamine in anemic Kenyan chil-dren (hemoglobin 7 to 109 gdL) [74] There was no reported increase in the susceptibility to clinical malaria or the prevalence of parasitemia at monthly screening associated with the iron supplementation alone or with IPT [16] whereas IPT plus iron was the most effective in increasing hemoglobin concentrations There were no significant statistical interactions between HbASAA phenotypes and treatment group However there was a nonsignificant increase in the incidence rate ratio of clinical malaria in the HbAS group not receiv-ing IPT during the 12 weeks of follow-up (IRR = 416 95 CI 05 to 346) and increased geometric mean parasite density in both groups but by far the biggest difference was seen in the group receiving IPT (6203 vs 1853 p = 08 for the interaction) The authors acknowledge that the number of clinical events was very small and that these findings would need veri-fication in a larger study since the number of HbAS individuals (approximately 25 to 30) in each treatment group versus approximately 100 HbAA individuals plus the short follow-up time means that the study was grossly underpowered to assess these outcomes If this

effect is real then the age group studied in this trial (2 to 36 months with 78 lt 18 months) should include the most affected although greater effects might be observed in areas of lower transmission and therefore also in a greater age range of children The results of these two trials warrant urgent further trials or retro-spective analysis of prior trials with sufficient power and detail to make firm conclusions on the effects of common polymorphisms on the response to iron sup-plementation which may be expected to vary by age group and transmission intensity

Clinical trials of IPT during infancy (IPTi) have demonstrated a reduction in the prevalence of anemia in young children in malaria-endemic areas [16 18 38 76] and in some trials a reduction in the incidence of clinical malaria [38 76] and morbidity and mortality in the first year of life [38 77] However the effects may vary depending on the timing of dosing choice of drug local levels of resistance and levels of transmission [78 79] On the basis of our analysis above the impact of IPTi plus iron supplementation may be modulated by levels of hemoglobinopathies and therefore suba-nalyses of these studies should be performed according to genotype wherever possible

Interactions of polymorphisms in host iron metabolism and regulatory proteins with malaria

Polymorphisms of haptoglobin a plasma protein that binds free hemoglobin released from lysed red blood cells recirculating the heme portion to the bone marrow through monocyte and macrophage uptake via CD136 have also been associated with malarial outcomes although reports are conflicting Hap-toglobin exists as three common phenotypes Hp1-1 1-2 and 2-2 In case-control studies in India Sudan Ghana and Cameroon the Hp2-2 phenotype has been associated with protection from severe malaria and placental infection [80ndash83] However two studies that have assessed associations with haptoglobin genotypes did not report any associations [84 85] In a cohort study in Gambian children the Hp2-2 genotype was associated with a greater drop in hemoglobin concen-trations across a malarial transmission season [65] The authors proposed that this effect may have been mediated through an increased prevalence of asymp-tomatic infection observed in the Hp2-2 group which contributed to anemia but could provide protection against severe malaria Interestingly similar but smaller drops in hemoglobin concentration were also observed for heterozygotes for G6PD and HbS We are currently analyzing the effects of low-dose iron supplementation during a malarial transmission season in a similar cohort of children

Inducible heme oxygenase (iHO-1) catalyzes the

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S536 A M Prentice et al

breakdown of heme to generate iron carbon monoxide and biliverdin and is expressed in monocytes and mac-rophages among other cells Biliverdin is subsequently degraded to bilirubin which has potent antioxidant effects Microsatellite polymorphisms in the number of tandem repeats in the promoter of iHO-1 have been variously associated with increased and decreased oxidant stress in various disease pathologies However in a case-control study of cerebral malaria patients in Myanmar homozygotes for the short number of repeats (lt 28) previously associated with higher levels of transcription of iHO-1 were significantly more likely to have cerebral malaria than uncomplicated malaria (odds ratio 314 p = 008) [86] It is not clear how this effect may be mediated but it is possible that it results from increased levels of free iron and resulting oxidant stress

In summary the mechanisms by which various genetic polymorphisms interact with malarial infec-tion are still not clear Furthermore it is not clear how they may affect a possible relationship between iron and malaria especially in relation to supplementation which should be differentiated from that of iron status The current evidence suggests that the heterozygous states of the hemoglobinopathies do not protect against malaria by a simple mechanism involving iron with-holding from the pathogen However the effects of iron supplementation in individuals with the most common polymorphisms should be carefully evaluated taking into account differences in transmission intensity and iron status at baseline

Conclusions

The evidence reviewed above tends to substantiate the concerns raised by the recent Pemba trial that universal administration of iron to children in malarious areas may be associated with adverse outcomes The mecha-nism by which this occurs is far from clear and merits

further research to test whether other chemical forms of supplementary iron might carry less risk There is also evidence that the risk profile will be altered by host genetic variations in hemoglobinopathies G6PD and genes regulating iron metabolism However these insights are not of great practical value because population screening and targeted supplementation programs are not feasible in the areas where iron defi-ciency is most prevalent Likewise the evidence that anemic children are probably at low risk for any adverse outcomes associated with iron supplementation implies a need for prescreening that may not be cost-effective or logistically feasible in developing-country settings

The evidence is fairly clear that malaria causes anemia by diverting iron away from bone marrow and erythropoiesis as part of the inflammatory response and hence iron administration alone is not likely to be the most effective means of combating the anemia Other therapeutic paradigms that combat the inflam-mation and adjust the timing of iron administra-tion to children recovering from malaria should be researched

We suggest that further research is still required to confirm the apparent relationships between iron status and malaria and that such studies should also focus on the underlying mechanisms of the putative interaction This might be achieved through the establishment of a multicountry collaboration to standardize protocols both for iron-supplementation interventions and for the assessment of iron and malaria status indicators Standardizing protocols across variations in age groups malaria transmission patterns and genetic distribu-tions of hemoglobinopathies will provide the evidence for a more targeted approach to policies of prevention and treatment of anemia in malaria-endemic regions

Until this evidence is gathered we recommend that iron supplementation in malarious areas must be accompanied by effective systems for ensuring univer-sal rapid access to diagnosis and treatment of malaria or by preventive therapy

References

1 WHO UNICEF Focusing on anaemia Towards an integrated approach for effective anaemia control Joint WHO UNICEF Statement Geneva Joint WHO UNICEF Statement 2004

2 Oppenheimer SJ Iron and its relation to immunity and infectious disease J Nutr 2001131616Sndash33S discussion 33Sndash35S

3 Murray MJ Murray AB Murray NJ Murray MB Diet and cerebral malaria the effect of famine and refeeding Am J Clin Nutr 19783157ndash61

4 Nyakeriga AM Troye-Blomberg M Dorfman JR Alexander ND Back R Kortok M Chemtai AK Marsh K Williams TN Iron deficiency and malaria among children living on the coast of Kenya J Infect Dis 2004 190439ndash47

5 Oppenheimer SJ Macfarlane SB Moody JB Bunari O Hendrickse RG Effect of iron prophylaxis on morbidity due to infectious disease report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 1986 80596ndash602

6 Shipton D Association between haemoglobin level and susceptibility to malaria a study of Gambian children [MSc dissertation] London London School of Hygiene and Tropical Medicine 2004

7 Snow RW Byass P Shenton FC Greenwood BM The relationship between anthropometric measurements and measurements of iron status and susceptibility to malaria in Gambian children Trans R Soc Trop Med Hyg 199185584ndash9

8 Asobayire FS Adou P Davidsson L Cook JD Hurrell

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S537Iron metabolism and malaria

RF Prevalence of iron deficiency with and without concurrent anemia in population groups with high prevalences of malaria and other infections a study in Cote drsquoIvoire Am J Clin Nutr 200174776ndash82

9 Allen SJ OrsquoDonnell A Alexander ND Alpers MP Peto TE Clegg JB Weatherall DJ alpha+-Thalassemia protects children against disease caused by other infec-tions as well as malaria Proc Natl Acad Sci U S A 1997 9414736ndash41

10 Murray MJ Murray AB Murray MB Murray CJ The adverse effect of iron repletion on the course of certain infections Br Med J 197821113ndash5

11 Smith AW Hendrickse RG Harrison C Hayes RJ Greenwood BM The effects on malaria of treatment of iron-deficiency anaemia with oral iron in Gambian children Ann Trop Paediatr 1989917ndash23

12 Oppenheimer SJ Gibson FD Macfarlane SB Moody JB Harrison C Spencer A Bunari O Iron supplementation increases prevalence and effects of malaria report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 198680603ndash12

13 Byles AB Drsquosa A Reduction of reaction due to iron dextran infusion using chloroquine Br Med J 19703625ndash7

14 Berger J Dyck JL Galan P Aplogan A Schneider D Traissac P Hercberg S Effect of daily iron supplementa-tion on iron status cell-mediated immunity and inci-dence of infections in 6ndash36 month old Togolese children Eur J Clin Nutr 20005429ndash35

15 Chippaux JP Schneider D Aplogan A Dyck JL Berger J [Effects of iron supplementation on malaria infection] Bull Soc Pathol Exot 19918454ndash62

16 Desai MR Mei JV Kariuki SK Wannemuehler KA Phil-lips-Howard PA Nahlen BL Kager PA Vulule JM ter Kuile FO Randomized controlled trial of daily iron sup-plementation and intermittent sulfadoxine-pyrimeth-amine for the treatment of mild childhood anemia in western Kenya J Infect Dis 2003187658ndash66

17 Nwanyanwu OC Ziba C Kazembe PN Gamadzi G Gandwe J Redd SC The effect of oral iron therapy during treatment for Plasmodium falciparum malaria with sulphadoxine-pyrimethamine on Malawian chil-dren under 5 years of age Ann Trop Med Parasitol 199690589ndash95

18 Verhoef H West CE Nzyuko SM de Vogel S van der Valk R Wanga MA Kuijsten A Veenemans J Kok FJ Intermittent administration of iron and sulfadoxine-py-rimethamine to control anaemia in Kenyan children a randomised controlled trial Lancet 2002360908ndash14

19 van den Hombergh J Dalderop E Smit Y Does iron therapy benefit children with severe malaria-associated anaemia A clinical trial with 12 weeks supplementation of oral iron in young children from the Turiani Division Tanzania J Trop Pediatr 199642220ndash7

20 Lawless JW Latham MC Stephenson LS Kinoti SN Pertet AM Iron supplementation improves appetite and growth in anemic Kenyan primary school children J Nutr 1994124645ndash54

21 Mebrahtu T Stoltzfus RJ Chwaya HM Jape JK Savioli L Montresor A Albonico M Tielsch JM Low-dose daily iron supplementation for 12 months does not increase the prevalence of malarial infection or den-sity of parasites in young Zanzibari children J Nutr 20041343037ndash41

22 Menendez C Kahigwa E Hirt R Vounatsou P Aponte JJ Font F Acosta CJ Schellenberg DM Galindo CM Kimario J Urassa H Brabin B Smith TA Kitua AY Tanner M Alonso PL Randomised placebo-controlled trial of iron supplementation and malaria chemoproph-ylaxis for prevention of severe anaemia and malaria in Tanzanian infants Lancet 1997350844ndash50

23 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S MrsquoBoge B Greenwood BM The effects of iron supplementation during pregnancy given by traditional birth attendants on the prevalence of anaemia and malaria Trans R Soc Trop Med Hyg 199488590ndash3

24 van Hensbroek MB Morris-Jones S Meisner S Jaffar S Bayo L Dackour R Phillips C Greenwood BM Iron but not folic acid combined with effective antimalarial therapy promotes haematological recovery in African children after acute falciparum malaria Trans R Soc Trop Med Hyg 199589672ndash6

25 Sazawal S Black RE Ramsan M Chwaya HM Stoltzfus RJ Dutta A Dhingra U Kabole I Deb S Othman MK Kabole FM Effects of routine prophylactic supplemen-tation with iron and folic acid on admission to hospital and mortality in preschool children in a high malaria transmission setting community-based randomised placebo-controlled trial Lancet 2006367133ndash43

26 Harvey PW Heywood PF Nesheim MC Galme K Zegans M Habicht JP Stephenson LS Radimer KL Brabin B Forsyth K et al The effect of iron therapy on malarial infection in Papua New Guinean schoolchil-dren Am J Trop Med Hyg 19894012ndash8

27 Andrews NC Iron homeostasis insights from genetics and animal models Nat Rev Genet 20001208ndash17

28 Kristiansen M Graversen JH Jacobsen C Sonne O Hoffman HJ Law SK Moestrup SK Identification of the haemoglobin scavenger receptor Nature 2001409 198ndash201

29 Wickramasinghe SN Abdalla SH Blood and bone marrow changes in malaria Baillieres Best Pract Res Clin Haematol 200013277ndash99

30 Phillips RE Looareesuwan S Warrell DA Lee SH Karbwang J Warrell MJ White NJ Swasdichai C Weatherall DJ The importance of anaemia in cerebral and uncomplicated falciparum malaria role of compli-cations dyserythropoiesis and iron sequestration Q J Med 198658305ndash23

31 Abdalla S Weatherall DJ Wickramasinghe SN Hughes M The anaemia of P falciparum malaria Br J Haematol 198046171ndash83

32 Sen R Bhatnagar BM Singh U Yadav MS Sehgal PK Patterns of erythropoiesis and anaemia in malaria J Commun Dis 199022247ndash53

33 Srichaikul T Wasanasomsithi M Poshyachinda V Panikbutr N Rabieb T Ferrokinetic studies and eryth-ropoiesis in malaria Arch Intern Med 1969124623ndash8

34 Das BS Thurnham DI Das DB Influence of malaria on markers of iron status in children implications for interpreting iron status in malaria-endemic communi-ties Br J Nutr 199778751ndash60

35 Menendez C Quinto LL Kahigwa E Alvarez L Fern-andez R Gimenez N Schellenberg D Aponte JJ Tanner M Alonso PL Effect of malaria on soluble transferrin receptor levels in Tanzanian infants Am J Trop Med Hyg 200165138ndash42

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S538 A M Prentice et al

36 Stoltzfus RJ Chwaya HM Montresor A Albonico M Savioli L Tielsch JM Malaria hookworms and recent fever are related to anemia and iron status indicators in 0- to 5-y old Zanzibari children and these relationships change with age J Nutr 20001301724ndash33

37 Stoltzfus RJ Chwaya HM Albonico M Schulze KJ Savioli L Tielsch JM Serum ferritin erythrocyte pro-toporphyrin and hemoglobin are valid indicators of iron status of school children in a malaria-holoendemic population J Nutr 1997127293ndash8

38 Massaga JJ Kitua AY Lemnge MM Akida JA Malle LN Ronn AM Theander TG Bygbjerg IC Effect of intermittent treatment with amodiaquine on anaemia and malarial fevers in infants in Tanzania a randomised placebo-controlled trial Lancet 20033611853ndash60

39 Verhoef H West CE Kraaijenhagen R Nzyuko SM King R Mbandi MM van Laatum S Hogervorst R Schep C Kok FJ Malarial anemia leads to adequately increased erythropoiesis in asymptomatic Kenyan children Blood 20021003489ndash94

40 Stoltzfus RJ Chway HM Montresor A Tielsch JM Jape JK Albonico M Savioli L Low dose daily iron supplementation improves iron status and appetite but not anemia whereas quarterly anthelminthic treatment improves growth appetite and anemia in Zanzibari preschool children J Nutr 2004134348ndash56

41 Kurtzhals JA Addae MM Akanmori BD Dunyo S Koram KA Appawu MA Nkrumah FK Hviid L Anae-mia caused by asymptomatic Plasmodium falciparum infection in semi-immune African schoolchildren Trans R Soc Trop Med Hyg 199993623ndash7

42 Loyevsky M John C Dickens B Hu V Miller JH Gordeuk VR Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators Mol Biochem Parasitol 199910143ndash59

43 Scholl PF Tripathi AK Sullivan DJ Bioavailable iron and heme metabolism in Plasmodium falciparum Curr Top Microbiol Immunol 2005295293ndash324

44 Darbari D Loyevsky M Gordeuk V Kark JA Castro O Rana S Apprey V Kurantsin-Mills J Fluorescence meas-urements of the labile iron pool of sickle erythrocytes Blood 2003102357ndash64

45 Ginsburg H Iron acquisition by Plasmodium spp Para-sitol Today 199915466

46 Atamna H Ginsburg H Heme degradation in the presence of glutathione A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells J Biol Chem 199527024876ndash83

47 Gabay T Ginsburg H Hemoglobin denaturation and iron release in acidified red blood cell lysatemdasha possible source of iron for intraerythrocytic malaria parasites Exp Parasitol 199377261ndash72

48 Iyer JK Shi L Shankar AH Sullivan DJ Jr Zinc pro-toporphyrin IX binds heme crystals to inhibit the proc-ess of crystallization in Plasmodium falciparum Mol Med 20039175ndash82

49 Cabantchik ZI Moody-Haupt S Gordeuk VR Iron che-lators as anti-infectives malaria as a paradigm FEMS Immunol Med Microbiol 199926289ndash98

50 Hershko C Control of disease by selective iron deple-tion a novel therapeutic strategy utilizing iron chelators Baillieres Clin Haematol 19947965ndash1000

51 Pradines B Tall A Ramiandrasoa F Spiegel A Sokhna C Fusai T Mosnier J Daries W Trape JF Kunesch G Parzy D Rogier C In vitro activity of iron-binding compounds against Senegalese isolates of Plasmodium falciparum J Antimicrob Chemother 2006571093ndash9

52 Meshnick SR Yang YZ Lima V Kuypers F Kam-chonwongpaisan S Yuthavong Y Iron-dependent free radical generation from the antimalarial agent artem-isinin (qinghaosu) Antimicrob Agents Chemother 1993371108ndash14

53 Golenser J Domb A Mordechai-Daniel T Leshem B Luty A Kremsner P Iron chelators correlation between effects on Plasmodium spp and immune functions J Parasitol 200692170ndash7

54 Nyakeriga AM Williams TN Marsh K Wambua S Perlmann H Perlmann P Grandien A Troye-Blomberg M Cytokine mRNA expression and iron status in chil-dren living in a malaria endemic area Scand J Immunol 200561370ndash5

55 Smith HJ Meremikwu M Iron chelating agents for treating malaria Cochrane Database Syst Rev 2003CD001474

56 Weatherall DJ The global problem of genetic disease Ann Hum Biol 200532117ndash22

57 Williams TN Maitland K Bennett S Ganczakowski M Peto TE Newbold CI Bowden DK Weatherall DJ Clegg JB High incidence of malaria in alpha-thalassaemic children Nature 1996383522ndash5

58 Rees DC Williams TN Maitland K Clegg JB Weather-all DJ Alpha thalassaemia is associated with increased soluble transferrin receptor levels Br J Haematol 1998103365ndash9

59 Maitland K Williams TN Bennett S Newbold CI Peto TE Viji J Timothy R Clegg JB Weatherall DJ Bowden DK The interaction between Plasmodium falciparum and P vivax in children on Espiritu Santo island Van-uatu Trans R Soc Trop Med Hyg 199690614ndash20

60 Weatherall DJ Clegg JB Genetic variability in response to infection malaria and after Genes Immun 2002 3331ndash7

61 Parikh S Dorsey G Rosenthal PJ Host polymorphisms and the incidence of malaria in Ugandan children Am J Trop Med Hyg 200471750ndash3

62 Destro Bisol G Genetic resistance to malaria oxidative stress and hemoglobin oxidation Parassitologia 1999 41203ndash4

63 Cappadoro M Giribaldi G OrsquoBrien E Turrini F Mannu F Ulliers D Simula G Luzzatto L Arese P Early phago-cytosis of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes parasitized by Plasmodium falciparum may explain malaria protection in G6PD deficiency Blood 1998922527ndash34

64 Arese P Turrini F Schwarzer E Band 3complement-mediated recognition and removal of normally senes-cent and pathological human erythrocytes Cell Physiol Biochem 200516133ndash46

65 Atkinson SH Rockett K Sirugo G Bejon PA Fulford A OrsquoConnell M A Bailey R Kwiatkowski DP Prentice AM Seasonal Childhood Anaemia in West Africa Is Associated with the Haptoglobin 2-2 Genotype PLoS Med 20063e172

66 Cabrera G Cot M Migot-Nabias F Kremsner PG Deloron P Luty AJ The sickle cell trait is associated

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S539Iron metabolism and malaria

with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens J Infect Dis 20051911631ndash8

67 Williams TN Mwangi TW Roberts DJ Alexander ND Weatherall DJ Wambua S Kortok M Snow RW Marsh K An immune basis for malaria protection by the sickle cell trait PLoS Med 20052e128

68 Ayi K Turrini F Piga A Arese P Enhanced phagocyto-sis of ring-parasitized mutant erythrocytes a common mechanism that may explain protection against falci-parum malaria in sickle trait and beta-thalassemia trait Blood 20041043364ndash71

69 Roberts DJ Harris T Williams T The influence of inherited traits on malaria infection In Bellamy R ed Susceptibility to infectious diseases the importance of host genetics Cambridge Cambridge University Press 2004 139ndash84

70 Williams TN Mwangi TW Wambua S Alexander ND Kortok M Snow RW Marsh K Sickle cell trait and the risk of Plasmodium falciparum malaria and other child-hood diseases J Infect Dis 2005192178ndash86

71 Aidoo M Terlouw DJ Kolczak MS McElroy PD ter Kuile FO Kariuki S Nahlen BL Lal AA Udhayakumar V Protective effects of the sickle cell gene against malaria morbidity and mortality Lancet 20023591311ndash2

72 Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K Nega-tive epistasis between the malaria-protective effects of alpha+-thalassemia and the sickle cell trait Nat Genet 2005371253ndash7

73 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S Ascaso C Smith T MrsquoBoge B Greenwood BM The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS Trans R Soc Trop Med Hyg 199589289ndash92

74 Terlouw DJ Desai MR Wannemuehler KA Kariuki SK Pfeiffer CM Kager PA Shi YP Ter Kuile FO Relation between the response to iron supplementation and sickle cell hemoglobin phenotype in preschool children in western Kenya Am J Clin Nutr 200479466ndash72

75 Duffy PE Fried M Malaria in the pregnant woman Curr Top Microbiol Immunol 2005295169ndash200

76 Schellenberg D Menendez C Kahigwa E Aponte J Vidal J Tanner M Mshinda H Alonso P Intermittent treatment for malaria and anaemia control at time of routine vaccinations in Tanzanian infants a randomised placebo-controlled trial Lancet 20013571471ndash7

77 Schellenberg D Menendez C Aponte JJ Kahigwa E Tanner M Mshinda H Alonso P Intermittent preventive antimalarial treatment for Tanzanian infants follow-up to age 2 years of a randomised placebo-controlled trial Lancet 20053651481ndash3

78 OrsquoMeara WP Breman JG McKenzie FE The promise and potential challenges of intermittent preventive treat-ment for malaria in infants (IPTi) Malar J 2005433

79 White NJ Intermittent presumptive treatment for malaria PLoS Med 20052e3

80 Elagib AA Kider AO Akerstrom B Elbashir MI Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan Trans R Soc Trop Med Hyg 199892309ndash11

81 Minang JT Gyan BA Anchang JK Troye-Blomberg M Perlmann H Achidi EA Haptoglobin phenotypes and malaria infection in pregnant women at delivery in western Cameroon Acta Trop 200490107ndash14

82 Quaye IK Ekuban FA Goka BQ Adabayeri V Kurtzhals JA Gyan B Ankrah NA Hviid L Akanmori BD Hap-toglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria Trans R Soc Trop Med Hyg 200094216ndash9

83 Singh IP Walter H Bhasin MK Bhardwaj V Sudhakar K Genetic markers and malaria Observations in Gujarat India Hum Hered 19863631ndash6

84 Aucan C Walley AJ Greenwood BM Hill AV Hap-toglobin genotypes are not associated with resistance to severe malaria in The Gambia Trans R Soc Trop Med Hyg 200296327ndash8

85 Bienzle U Eggelte TA Adjei LA Dietz E Ehrhardt S Cramer JP Otchwemah RN Mockenhaupt FP Limited influence of haptoglobin genotypes on severe malaria in Ghanaian children Trop Med Int Health 200510668ndash71

86 Takeda M Kikuchi M Ubalee R Na-Bangchang K Ruangweerayut R Shibahara S Imai S Hirayama K Microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with susceptibility to cerebral malaria in Myanmar Jpn J Infect Dis 2005 58268ndash71

87 Shankar AH Nutritional modulation of malaria mor-bidity and mortality J Infect Dis 2000182 Suppl 1 S37ndash53

88 Gera T Sachdev HP Effect of iron supplementation on incidence of infectious illness in children systematic review Bmj 20023251142

Page 4: Iron metabolism and malaria

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S527Iron metabolism and malariaM

enen

dez [

23]

Tran

s R S

oc T

rop

Med

H

yg 1

994

Mul

tigra

vid

preg

nant

w

omen

iro

n (2

00 m

g fe

rrou

s sul

fate

) vs

plac

ebo

N =

550

Dat

a no

t ava

ilabl

ePC

V gt

25

Mea

n H

b =

10g

dL at

ba

selin

e

Act

ive

trea

tmen

t of

mal

aria

inci

dent

cas

esD

ecre

ased

pre

vale

nce

of

anem

ia a

nd o

f iro

n de

fi-ci

ency

Ir

on su

pple

men

tatio

n w

as n

ot

signi

fican

tly a

ssoc

iate

d w

ith

susc

eptib

ility

to p

reva

lenc

e or

se

verit

y of

mal

aria

van

Hen

sbro

ek [2

4]Tr

ans R

Soc

Tro

p M

ed

Hyg

199

56

mondash

9 yr

chl

oro-

quin

e vs

SP

+ ra

n-do

miz

atio

n to

iron

(asymp

100

mg

elem

enta

l iro

n) v

s fo

late

vs

pla-

cebo

N =

530

All

child

ren

wer

e re

crui

ted

at cl

inic

w

ith u

ncom

plic

ated

m

alar

ia

74

had

Hb

lt 11

g

dL at

bas

elin

eA

ll ch

ildre

n re

ceiv

ed

trea

tmen

t for

mal

aria

as

par

t of t

he tr

ial

Iron

gro

up h

ad m

ean

incr

ease

in

Hb

= 0

81 g

dL

Fola

te su

pple

men

tatio

n di

d no

t im

prov

e he

mat

olog

ical

pa

ram

eter

s and

incr

ease

d ra

te

of tr

eatm

ent f

ailu

re in

chil-

dren

rece

ivin

g SP

Ir

on d

id n

ot a

ffect

susc

eptib

il-ity

to m

alar

ia

Nw

anya

nwu

[17]

Ann

Tro

p M

ed P

aras

i-to

l 199

6lt

5 yr

SP

vs S

P +

daily

iron

(25

mg

kg fe

rrou

s sul

fate

) vs

SP

+ w

eekl

y iro

n

N

= 2

22

Incl

usio

n cr

iterio

n

para

site

dens

itygt

500

microl w

hole

blo

od

Hb

ge 5

gdL

All

wer

e tr

eate

d w

ith

SPD

aily

iron

+ S

P H

b in

crea

sed

49

gdL

vs

35ndash

37

gdL

in

SP a

nd S

P +

wee

kly

iron

G

reat

est b

enef

it on

Hb

in H

b gr

oup

5ndash8

gdL

at b

asel

ine

Iron

gro

ups h

ad in

crea

sed

trea

tmen

t fai

lure

vs

SP a

lone

(N

S)

van

den

Hom

berg

h [1

9]

J Tro

p Pe

diat

r 199

6lt

30 m

o ir

on (2

00

mg

ferr

ous s

ulfa

te) +

fo

late

vs

fola

te o

nly

N =

100

Onl

y in

clud

ed ch

il-dr

en w

ith p

aras

ite-

posit

ive

thic

k fil

ms

Hb

le 5

gdL

All

rece

ived

trea

tmen

t w

ith S

P +

quin

ine

40

rece

ived

blo

od tr

ans-

fusio

n

Diff

eren

ces i

n ba

selin

e ch

arac

-te

ristic

s (H

b p

aras

ite d

ensit

y be

twee

n gr

oups

)N

o sig

nific

ant d

iffer

ence

in

chan

ge in

Hb

betw

een

grou

psN

o di

ffere

nces

in m

alar

ia in

di-

ces b

etw

een

grou

ps

Men

ende

z [22

] La

ncet

199

72ndash

12 m

o ir

on (2

mg

kg fe

rrou

s gly

cine

sul-

fate

) + D

elta

prim

vs

iron

vs D

elta

prim

vs

plac

ebo

N =

832

24

of c

hild

ren

wer

e pa

rasit

emic

at b

ase-

line

PCV

gt 2

5Pa

ssiv

e ca

se d

etec

tion

plus

hig

h us

e of h

ealth

se

rvic

es

Iron

supp

lem

enta

tion

decr

ease

d an

emia

by

288

and

mal

aria

chem

opro

phy-

laxi

s dec

reas

ed a

nem

ia b

y 60

5

Iron

supp

lem

enta

tion

had

no

effe

ct o

n fr

eque

ncy

of m

alar

iaco

ntin

ued

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S528 A M Prentice et al

Berg

er [

14]

Eur J

Clin

Nut

r 200

06ndash

36 m

o iro

n (2

ndash3

mg

kg ir

on b

atai

n-at

e) v

s pl

aceb

o

N

= 1

97

62

of c

hild

ren

wer

e pa

rasit

emic

at

base

line

Hb

ge 8g

dL

Act

ive

mor

bidi

ty

follo

w-u

p an

d tr

eat-

men

t of a

ll fe

vers

w

ith a

ntim

alar

ials

Prev

alen

ce o

f iro

n-de

ficie

ncy

anem

ia d

ecre

ased

in ir

on

grou

p an

d in

crea

sed

in p

la-

cebo

gro

upA

ll m

arke

rs o

f iro

n st

atus

wer

e sig

nific

antly

hig

her i

n iro

n gr

oup

Incr

ease

in p

erce

ntag

e of

chil-

dren

with

par

asite

mia

gt 3

000

in

iron

gro

up (N

S)

Verh

oef [

18]

Lanc

et 2

002

2ndash36

mo

iron

(6 m

gkg

wk

ferr

ous f

uma-

rate

) vs

SP v

s iro

n +

SP v

s pl

aceb

o

N

= 3

28

Onl

y as

ympt

omat

ic

mal

aria

incl

uded

(3

0 d

ipst

ick

posi-

tive

at b

asel

ine)

Hb

6ndash11

gd

L A

ctiv

e fo

llow

-up

of

feve

rs a

nd tr

eatm

ent

upon

dia

gnos

is

SP a

lone

incr

ease

d H

b by

03

1 g

dLIr

on +

SP

incr

ease

d H

b by

11

1 g

dLIr

on a

lone

incr

ease

d H

b by

10

7 g

dLIn

crea

se in

mal

aria

risk

with

iro

n su

pple

men

tatio

n (N

S)

Des

ai [1

6]J I

nfec

t Dis

2003

2ndash36

mo

IPT

+ iro

n (3

ndash6 m

gkg

ferr

ous

sulfa

te) v

s iro

n vs

IP

T vs

pla

cebo

N

= 5

46

26

of c

hild

ren

wer

e pa

rasit

emic

at b

ase-

line

(are

a of

hig

h IT

N u

se

Hb

7ndash10

9 g

dL

Pass

ive

surv

eil-

lanc

e sy

stem

and

ac

tive

trea

tmen

t of

mal

aria

and

ane

mia

(4

-wee

kly

visit

s)

Iron

gro

up h

ad m

ean

incr

ease

in

Hb

of 0

88g

dL

Ir

on +

IPT

mea

n in

crea

se in

H

b =

114

gd

LIn

crea

se in

mal

aria

par

asite

mia

(N

S) H

R =

114

N

o ef

fect

on

HR

of cl

inic

al

mal

aria

Meb

raht

u [2

1]J N

utr 2

004

4ndash71

mo

iron

(10

mg

ferr

ous s

ulfa

te) v

s iro

n +

meb

enda

zole

vs

meb

enda

zole

+

plac

ebo

vs p

lace

bo

supp

lem

ente

d fo

r 12

mo

N =

614

84

of c

hild

ren

wer

e pa

rasit

emic

at

base

line

94

had

Hb

lt 11

gd

LA

ctiv

e su

rvei

llanc

e no

trea

tmen

tIn

crea

sed

seru

m fe

rriti

nD

ecre

ased

zinc

pro

topo

rphy

rin

in su

pplem

ente

d gr

oup

N

o di

ffere

nce

in m

alar

iom

etric

in

dice

s (pr

eval

ence

or p

ara-

sitem

ia)

but c

linic

al v

alue

s no

t ass

esse

d

Tabl

e 2

Pub

lishe

d tr

ials

of o

ral i

ron

supp

lem

enta

tion

and

mal

aria

risk

Firs

t aut

hor

Sour

ce a

nd y

ear

Stud

y de

sign

Mal

aria

at b

asel

ine

Iron

stat

us in

clus

ion

crite

ria

Cas

e de

tect

ion

and

trea

tmen

t of m

alar

ia

inci

dent

cas

esFi

ndin

gs

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S529Iron metabolism and malaria

partly explain the variations in response to iron supple-mentation reported by different studies other potential complicating factors that contribute to these variations are described in table 4

All but two studies [15 19] have found significant positive effects on markers of iron status in those receiving iron supplementation In the trial of van den Hombergh et al [19] the sample size was limited and baseline characteristics were significantly different between the supplementation and placebo groups Chippaux et al [15] found that anemic children who remained parasite free had increased hemoglobin levels postsupplementation but those that subsequently developed malaria did not The effect of supplementa-tion on hemoglobin concentrations ranged between 06 and 49 gdL with the highest increase occurring in a study that combined iron supplements with anti-malarial therapy [17] Other studies have also shown an additional advantage of iron plus antimalarials as regards hemoglobin recovery [16 18] However despite the hematological benefits all of these studies found nonsignificant increases in adverse malarial outcomes in the groups that received antimalarials plus iron including increased parasite density [16] risk of malaria [18] and treatment failure [17]

Six studies found no effect of iron supplements on malaria risk [19ndash24] of these three included large proportions of anemic subjects (74 to 94) [20 21 24] and one included only children with hemoglobin lt 5 gdL [19] Other studies that stratified by baseline hemoglobin levels [17 25] found that the greatest ben-efits occurred in the most anemic subgroups

Three studies found an increase in clinical malaria attacks in the iron-supplemented groups [10 11 25] and a further six studies found nonsignificant increases in malaria outcomes [14ndash18 26] One of the striking differences between study populations with significant increases in malaria outcomes and those with non-significant effects is access to health care and active treatment of malaria incident cases In fact all but one of the trials [21] that found no effect on malaria outcomes provided access to health care facilities or active follow-up and treatment of malaria incident cases This implies that the potential detrimental effects of iron supplementation may be curtailed by concurrent effective treatment of malaria infections However Verhoef et al and Nwanyanwu et al have shown potential treatment failure effects of combining sulfadoxinendashpyrimethamine with iron in the treatment of preexisting malaria suggesting that antimalarial therapy should precede supplementation [2 17 18]

These observations are further confirmed by a large study in Zanzibar by Sazawal et al [25] that showed increases in malaria-related morbidity and mortality in the iron-supplemented arms of a randomized control-led trial of ironfolate and ironfolate plus zinc versus placebo (summarized in table 2) A subgroup of this Sa

zaw

al[2

5]La

ncet

200

61ndash

35 m

o ir

on (1

25

mg)

+ fo

late

vs

iron

+ fo

late

+ zi

nc v

s pl

aceb

o m

orbi

d-ity

and

mor

talit

y ou

tcom

es a

sses

sed

N

= 3

215

5

43

wer

e pa

rasit

emic

at

bas

elin

eH

b gt

7 g

dL 5

7 o

f ch

ildre

n ha

d H

b lt

10 g

dL

at b

asel

ine

Trea

ted

subs

tudy

chil-

dren

with

clin

ical

m

alar

ia w

ith S

P at

ba

selin

e 6

mo

and

12

mo

Com

bine

d iro

n gr

oups

vs

pla-

cebo

Fo

r adv

erse

mal

aria

-rel

ated

ev

ents

RR

= 1

16

For c

ereb

ral m

alar

ia R

R =

122

Iron

+ fo

late

vs

plac

ebo

For c

ereb

ral m

alar

ia a

s a c

ause

of

dea

th R

R =

17

Subs

tudy

Lo

wer

rate

of a

dver

se e

vent

s in

child

ren

iron

defic

ient

at

base

line

Prot

ectiv

e ef

fect

of i

ron

+ fo

late

in

iron

-def

icie

nt a

nem

ic ch

il-dr

en R

R =

051

Sig

nific

ant d

iffer

ence

s as

repo

rted

by

the

auth

ors

RCT

ran

dom

ized

con

trol

led

tria

l H

b h

emog

lobi

n O

R o

dds

ratio

MC

V m

ean

corp

uscu

lar

volu

me

NS

not

sig

nific

ant

PCV

pac

ked

cell

volu

me

SP

sul

fado

xine

ndashpyr

imet

ham

ine

IPT

inte

rmitt

ent

prev

entiv

e th

erap

y IT

N i

nsec

ticid

e tr

eate

d be

dnet

s ]H

R h

azar

d ra

tio R

R re

lativ

e ris

k

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S530 A M Prentice et al

trial was investigated in more detail and consequently received more intensive diagnosis and treatment of malaria and other infections Substudy children with iron-deficiency anemia at baseline benefited sig-nificantly from iron supplementation in that they had reduced malaria and other infection-related hospital admissions and mortality [25]

The results of this recent study in Zanzibari children have raised new concerns about possible serious side effects of iron supplementation in populations where the etiology of anemia is not solely attributable to iron

deficiency and point to the need for a deeper under-standing of the complex biology of iron sequestration and redistribution between different storage and functional compartments and of the underlying host factors that influence these processes

Effect of malaria on iron metabolism

Erythropoietic iron requirement is met largely through recycling of senescent red blood cells through reticu-loendothelial macrophages where iron is repackaged onto transferrin for transport to the bone marrow [27] Red blood cells are predominantly engulfed directly by reticuloendothelial macrophages however up to 10 of normal recycling occurs as a result of intravascular hemolysis Hemoglobin is released and rapidly bound to haptoglobin and the resultant complex is cleared by liver parenchymal cells or the CD163 macrophagal receptor [28] Malaria-induced destruction of infected and noninfected red blood cells both stresses and impedes the capacity of reticuloendothelial macro-phages to recycle iron back to the bone marrow Intra-vascular rupture of parasitized red cells macrophagal phagocytosis of both parasitized and unparasitized red cells and hypersplenism all contribute to the patho-physiology of the anemia associated particularly with acute malaria

The local epidemiology and transmission character-istics of Plasmodium falciparum together with local drug treatment and intermittent preventive therapy

TABLE 3 Meta-analyses and reviews

First author Sourceyear Study design Findings

Shankar [87] J Infect Dis 2000 Meta-analysis of 13 RCTs of the effect of iron supplementation on malaria and iron status

RR for clinical malaria attack = 11 (NS)RR for slide positive for Plasmodium falci-

parum = 117Absolute increase in infection rate = 57 (NS)RR for spleen enlargement = 112 (NS)Mean increase in Hb = 125 gdLRR for anemia = 05

Oppenheimer [2] J Nutr 2001 Review of controlled interven-tion studies of iron supplemen-tation

Oral iron therapy increased clinical malaria in 5 out of 9 studies

No studies of iron therapy in malarious areas showed benefits on infectious morbidity

Does not report on effect on iron status

Gera [88] BMJ 2002 Systematic review of 28 RCTs of the effect of iron supplementa-tion or fortification in children on infectious illness (including 8 studies of the effect of iron supplementation on malaria)

Pooled OR for malaria-positive smear = 143 but OR when adjusted for baseline malaria smear = 124 (NS)

(The treatment effect increased by 289 times per unit increase in baseline malaria posi-tivity this supports the argument that iron supplementation of children with preexist-ing malaria increases their risk of remaining malaria positive)

Significant differences as reported by the authors RCT randomized controlled trial RR relative risk NS not significant Hb hemoglobin OR odds ratio

TABLE 4 Factors complicating assessment of the relationship between iron status and malaria and the response to iron sup-plementation in malaria-endemic populations

raquo Differences in dose duration and route of iron admin-istration

raquo Degree of malaria immunity in study individuals which can also be related to age and local malaria transmission patterns [7]

raquo Supplementation with iron and folate vs iron alone (especially as some antimalarials have antifolate action) [24]

raquo Markers of iron status used (the confounding effect of infection on serum markers of iron deficiency) [2 8]

raquo Baseline iron status iron-deficient individuals benefit [18 21]

raquo Access to health care and intensity of malaria surveil-lance and treatment during the trial [18 25]

raquo Hemoglobinopathies may affect anemia and response to iron supplementation as well as risk of malaria [9 73]

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S531Iron metabolism and malaria

(IPT) practices influence population immunity and resultant malarial clinical presentation as well as the epidemiology of anemia in a particular setting These factors may also influence the disturbance of iron metabolism and erythropoietic response to iron sup-plementation Acute malaria is associated predomi-nantly with a picture of fever hemolysis and oxidant stress whereas dyserythropoiesis predominates in the anemia of chronic malaria in a semiimmune patient [29] Acute malarial hemolysis represents a major stress on the homeostatic mechanisms of iron flux regulation that have evolved primarily to maintain erythroblast supply while minimizing the oxidant stress-associated effects of iron

Iron can be sequestered and trapped in reticuloen-dothelial macrophages as a result of both chronic and acute malaria and can present a picture of iron-deficient erythropoiesis associated with normal or increased bone marrow iron For instance bone marrow aspirates in 23 Thai patients with uncomplicated acute malaria (age 15 to 52 years) demonstrated malarial pigment in 22 of them Convalescent bone marrow aspirates in 16 patients (3 to 25 days after admission) demonstrated increased iron content compared with the admission sample [30] Five of six Gambian children (lt 5 years of age) with acute malaria had elevated stainable bone marrow iron and four of six children with chronic malaria and severe anemia (hemoglobin lt 6 gdL) had either normal or markedly increased levels of bone marrow stainable iron [31] Eighty-six percent of Indian children and adults (N = 26) with acute and 84 of those with chronic falciparum malaria and anemia (mean hemoglobin 54 gdL N = 38) had normal or increased bone marrow iron stores [32] Ferrokinetic studies involving the intravenous administration of 59Fe demonstrated low unsaturated iron-binding capacity and a rapid plasma iron disappearance time in both parasitemic and postparasitemic patients with acute and secondary (recent acute infection with persistent parasitemia) P falciparum and P vivax in Thai adults compared with controls [33] Incorporation of 59Fe into red blood cells was decreased in acute (N = 5) and secondary parasitemia (11 of 14) but found to be largely normal in the postparasitemic patients includ-ing 3 who were restudied from the parasitemic group Iron sequestration in acute malaria is cytokine driven (elevated tumor necrosis factor α [TNF-α] ILndash1 and interferon γ [IFN-γ] and diminished ILndash10) [29] prob-ably mediated via hepcidin however quantifying this phenomenon assessing how long it persists after acute malaria and in association with chronic malaria and assessing its importance in relation to malarial anemia malaria-associated immunosuppression and response to iron supplementation is difficult since there are few data Conventional indices of iron storage (eg ferritin) or of tissue supply (eg zinc protoporphyrin soluble transferrin receptor transferrin saturation) are

affected by inflammation [8 34ndash36] and the assess-ment of the iron status of young children in malarious areas with acute or chronic malaria is problematic [34] In a holoendemic environment ferritin and eryth-rocyte protoporphyrin were not affected by chronic malaria in older children [37] These indices also do not distinguish between iron deficiency and iron sequestration

Effect of malaria on response to iron supplementation

Malaria-induced anemia does not lead to loss of iron from the body However iron deficiency often coex-ists with malaria in areas of malaria transmission and therapy for severe postmalarial anemia commonly assumes a component due to preexisting iron defi-ciency Iron supplements are routinely prescribed both for severe malaria-associated anemia and for presumed iron-deficient anemia in a malaria-endemic environ-ment Few studies however have looked at the effect of acute malaria on the response to iron supplementation and even fewer have addressed the effect of chronic asymptomatic malaria More commonly studies either have either assessed the response to supplementation of children with anemia of undefined etiology in areas of coexistent malaria iron deficiency and hookworm or have randomized children who were anemic after malaria to a variety of hematinics In a study of 222 Malawian children (lt 5 years of age) with anemia after acute malaria the use of Fansidar and daily supplemen-tal iron resulted in a significantly greater hemoglobin recovery than Fansidar alone or Fansidar and weekly iron only in those children with initial hemoglobin between 5 and 8 gdL [17] However a larger propor-tion of the iron-treated children failed to clear their malaria In the Gambia 600 children (mean age 52 months mean hemoglobin 96 gdL) with uncompli-cated falciparum malaria randomized to receive chlo-roquine or Fansidar as treatment and then either iron folic acid or placebo for 28 days [22] demonstrated a significantly better hemoglobin response with iron than with placebo or folic acid (the difference in mean hemoglobin level after 1 month was 07 gdL) One hundred Tanzanian children (lt 30 months of age) with severe anemia (hemoglobin lt 5 gdL) were randomized either to receive daily iron supplementation or to be controls after antimalarial treatment [19] Among the 60 who completed the 12-week follow-up without a transfusion (30 in each group) there were no differ-ences in hemoglobin recovery From these studies the role of iron supplementation in the treatment of anemia after acute malaria is unclear and it is likely that the hemoglobin response to supplementation is influenced by both the direct inflammatory effect of malaria on iron absorption and utilization and preexistent iron

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S532 A M Prentice et al

deficiency which is impossible to assess in the presence of malaria In the Gambia we recently compared the absorption of stable-isotope-labeled iron in children anemic as a result of iron deficiency and children anemic after acute malaria Both groups were given 30 days of iron supplementation and the malaria group demonstrated significantly better hemoglobin recovery despite initially significantly reduced iron absorption (Doherty et al unpublished results) Utilization of sequestered iron is likely to be a major contributor to erythroblastic iron requirement after acute malaria

Studies of iron supplementation of populations of anemic children in malarious areas have reported either improved hemoglobin response or decreased prevalence of severe anemia [16 22 38 39] Incorpo-ration of antimalarial intervention arms is common Malaria transmission characteristics study design use of antecedent antimalarials differing iron supplemen-tation doses and differing outcome measures as well as different prevalence rates of iron deficiency and hook-worm infection have made the assessment of factors affecting hemoglobin response to iron supplementation difficult In particular the effect of chronic malaria on response to supplementation in high-transmission areas is unclear as the etiology of the anemia and the chronicity of malaria parasitemia are often undefined in study subjects In an area of intense transmission in Tanzania in which more than 80 of children (4 to 71 months old) were parasitemic at baseline and where malaria infection was strongly associated with hemo-globin supplementation improved the iron status and motor and language development of an iron-deficient population but not did not improve hemoglobin [21 36 40] The authors concluded that factors including malarial parasitemia or ineffective erythropoiesis due to inflammatory processes in a population with high levels of infectious morbidity and inflammation might have limited erythropoiesis

An inflammatory-mediated block to iron absorp-tion and utilization is likely to limit the erythropoietic response to supplemental iron after acute malaria how-ever it is unclear whether chronic parasitemia similarly limits the response to supplemental iron The asso-ciation of chronic malaria with anemia [39] stainable bone marrow iron [34] and increased cytokine levels [41] might suggest a probable effect and the eradica-tion of parasites has been associated with hemoglobin improvement without supplemental iron [31]

Iron metabolism by malaria parasites

In this section we consider whether the availability of iron in the host could modulate the efficiency with which malaria parasites can establish an infection and the severity of that infection What evidence is there to support the ldquonutritional immunityrdquo hypothesis that

host iron availability could limit parasite invasion or multiplication andor the clinical sequelae of para-site infection Support for the nutritional immunity hypothesis first stated in the 1970s has generally waned for the majority of pathogens [2] but there may still be a case for obligate intracellular pathogensmdashincluding Plasmodium spp

It may be informative to examine the research of other scientists than those typically involved in the cur-rent debate For example in order for this hypothesis to be truemdashat least in terms of the success of parasite invasion and replicationmdashit is a requirement that P falciparum be dependent on host iron sources for its survival Next is iron deficiency ever likely to be a limiting factor in the supply of iron to the parasite The most recent research suggests that P falciparum does utilize iron from the host but not from the abundant supplies available in erythrocyte hemoglobin the heme portion of which is quickly degraded to nontoxic but non-iron-bioavailable hemozoin or from the plasma via transferrin but from another source possibly an intraerythrocytic labile pool of ferrous iron [42 43] Interestingly measurements of this labile ferrous iron in normal and sickled erythrocytes indicate it to be positively associated with hemoglobin concentrations and negatively associated with plasma ferritin [44] However other researchers have reported evidence to suggest that the degradation of heme to hemozoin is incomplete and that 50 of heme may be degraded via an alternative pathway involving reduced glutathione and releasing bioavailable iron [45 46] As it has been estimated that less than 1 of heme iron would be sufficient to meet parasite iron requirements [47] iron deficiency would never induce iron-limited growth if hemoglobin were the iron source for parasites

Another mechanism by which iron deficiency may limit parasite growth is that proposed recently by Iyer et al [48] who demonstrated the inhibition of hemozoin formation from toxic free heme by the naturally occur-ring zinc protoporphyrin IX (ZPP) at levels likely to be encountered in anemic erythrocytes It is interesting to note that this is thought to be the mechanism by which the quinoline antimalarials act Furthermore Iyer et al demonstrated that quinolines competed for ZPP bind-ing and prevention of hemozoin formation It is pos-sible that via this mechanism moderate anemia could allow the persistence of low levels of parasitemia and therefore affect the development of exposure-related antibody repertoire and clinical immunitymdashwith consequent effects on future malarial incidence and malaria-associated anemia However the evidence for such an effect in human populations is currently limited due to the lack of longitudinal studies assessing ZPP levels and parasite prevalence and density from infancy onwards

Another research area that has been used to support the hypothesis of decreased iron availability is that

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S533Iron metabolism and malaria

of the effects of iron chelators on parasite growth in vitro and in vivo [49 50] Furthermore some antima-larial drugs such as the antibiotic cyclines including doxycycline are also iron chelators However iron chelators may not be acting by depriving the parasite of iron Alternative mechanisms have been suggested for some chelators including the induction of reactive oxygen species from dissociation of iron from heme and hemozoin as suggested for the lipophilic FR160 [51] similar to the suggested mechanism of artemisinin [52] Furthermore differences between the efficacy of chelators in vitro and in vivo have been associated with differences in immune modulation [53] This may suggest that iron status could affect malarial outcomes via direct effects on immune modulation as suggested by Nyakeriga et al [54] The evidence base for the effects of current iron-chelator therapies in reducing the prevalence density or clinical sequelae of malaria is weakmdashas outlined in a recent Cochrane review of clinical trials involving the use of either desferioxamine or the orally available deferiprone [55] in which all of the seven studies included had limitations relat-ing to study size relevance of study populations and more critically methodological and analytical faults However the authors of this review concluded that the results suggested possible benefits of treatment in cerebral malaria with a shorter recovery time from coma and decreased time to parasite clearance The initial justification for using iron-chelator therapy in cerebral malaria was based on the premise of prevent-ing iron-induced damage to brain cells resulting from hemolysis Therefore it is important to note that the possible benefits of iron-chelator therapy may not relate to limitation of iron for parasite growth and may there-fore not provide evidence in support of the nutritional immunity hypothesis

Iron malaria and hemoglobinopathies

How do hemoglobinopathies protect against parasite invasion or multiplication andor clinical sequelae of parasite infection Are these polymorphisms likely to affect the relationship between iron status or supple-mentation and malaria

J B S Haldane is credited with first postulat-ing heterozygote selection as an explanation for the high prevalence of the thalassemias and later other hemoglobinopathies He suggested that the small size reduced hemoglobin concentrations and increased resistance to hypertonic solutions of such cells may result in decreased parasite invasion or growth Although this hypothesis has been widely accepted for some time it has only recently been possible to dem-onstrate that these mutations have been maintained by selection mostly by malaria but possibly also other infectious causes However the extent and mechanisms

of protection are still debated At least in vitro many studies have failed to demonstrate decreased ability of parasites to invade or grow in thalassemic cells or cells containing hemoglobin S (HbS) Instead the mecha-nisms appear to be more complicated and possibly to vary between local conditions

The common polymorphisms involved in hemo-globin synthesis or red cell formation include sickle hemoglobin (HbS) HbC and HbE the α and β-thalassemias and South Asian ovalocytosis The geographic distribution of these varies across tropi-cal areas and can vary extensively even within closely related regions Current estimates of these polymor-phisms are often based on single sites and are likely to be underestimates [56] but a figure of 27 million carriers of the main hemoglobinopathies has been proposed [56] The carrier frequency for HbS is esti-mated at between 5 and 40 in populations across sub-Saharan Africa the Middle East and parts of South Asia HbC is limited to parts of West and North Africa whereas HbE is common in some parts of India and Southeast Asia with carrier rates up to 60 The thalassemias have the broadest geographic distribution and also the widest range of causative mutations and clinical outcomes The carrier frequencies for the more severe range of β-thalassemias is generally lower than for the α-thalassemias which are estimated to reach carrier frequencies of up to 20 in sub-Saharan Africa higher in Middle Eastern and Indian populations and up to 80 in some Pacific populations (reviewed in Williams et al [57] Rees et al [58] and Maitland et al [59])

In β-thalassemias excess α-globin chains precipitate in red cell precursors leading to ineffective erythropoi-esis and resulting in anemia in the context of increased iron absorption and iron accumulation The clinical expression of β-thalassemia varies widely depending on the exact genetic lesions inherited and interactions with other genetic loci including the α and γ globin genes β-Thalassemia trait and β-thalassemia interme-diate are often asymptomatic and may not be diagnosed except for mild anemia In α-thalassemia the excess β-chains form stable homotetramers which do not sig-nificantly affect erythropoiesis but cause an increased rate of hemolysis of mature cells The degree of the deficit of α-globin chains depends on the number of α-globin genes inactivated and unless three α-globin genes are lost the effects are subtle and various so that the condition will go largely undiagnosed It might be supposed that iron supplementation could be more deleterious in populations with a high prevalence of β-thalassemia mutations because of the inability to utilize the iron leading to increased iron availability to pathogens or iron-induced oxidant stress Interest-ingly Oppenheimer [2] reported that the increased susceptibility to malaria associated with parenteral iron in Papua New Guinean children was not apparent in

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S534 A M Prentice et al

single-deletion α-thalassemia compared with normal children

In a prospective casendashcontrol study in Papua New Guinea α-thalassemic α+ndash homozygotes and α+ndash heterozygotes had a greatly decreased risk of severe malaria (incidence rate ratio = 04 and 066) compared with controls [9] Furthermore protection was also observed for hospitalization from other infections possibly suggesting an immune component to the pro-tection [60] although the reduction of severe malaria may reduce infectious sequelae by invasive bacte-rial disease In apparent contrast α-thalassemia has also been associated with an increased prevalence of uncomplicated malaria in Vanuatu particularly in very young children with P vivax [57] It was suggested that increased red cell turnover in these children increased susceptibility to P vivax [58] resulting in cross-species immunity to P falciparum in later life [59] A similar finding was reported for glucose-6-phosphate dehy-drogenase (G6PD) deficiency in a cohort study in Uganda in which many other potential risk factors for malarial infection were controlled for (age water source use of prophylaxis bednet usage and proxim-ity to mosquito breeding sites) Female heterozygotes for G6PD had a significantly increased incidence of uncomplicated malaria (IRR = 13 p = 03) and a trend for increased parasite densities similar trends were seen for hemizygote males This was different from the pattern observed for HbS heterozygotes who had a nonsignificantly decreased incidence of uncomplicated malaria and decreased parasite densities [61]

A mechanism that has been suggested for G6PD defi-ciency and that may also be applicable to sickle (HbAS) and thalassemic cells involves decreased oxidative protection (G6PD) or increased constitutive oxidative stress of these cells (HbAS αβ thalassemias) especially when infected resulting in increased clearance of the cells from non-malaria-specific immune mechanisms essentially the same as the normal removal of old ldquosenescentrdquo red cells by phagocytes [62ndash64] It has been proposed that such a mechanism could prevent parasitemias from reaching critically high densities and therefore protect from severe malaria and also facilitate the development of antibody repertoires in children from the maintenance of low-grade infections in young children [65ndash67] In a slight modification of this hypothesis the increased phagocytic removal of early ring-stage infected cellsmdashcompared with schizonts and trophozoitesmdashhas been demonstrated for G6PD β-thalassemic and HbAS cells in vitro but not for α-thalassemic infected cells [68] The phagocytosis of ring compared with later stages may be advantageous since rings contain less hemozoin the buildup of which in monocytes has been associated with decreased func-tion Additionally the reduction of the later stages of parasite development may reduce the development of severe symptoms such as cerebral malaria from

reduced endothelial adhesion of late-stage infected red blood cells to receptors such as intracellular adhesion molecule-1 (ICAM-1)

The epidemiological evidence for a protective effect of HbAS suggests that the protective effects are great-est for severe disease (reviewed by Roberts et al [69]) In the most comprehensive study to date a detailed prospective cohort in two Kenyan populations it was reported that HbS heterozygotes had a significantly decreased risk of mild clinical malaria as assessed by active surveillance (50 decreased risk 95 confi-dence interval [CI] 26 to 67]) a 75 (95 CI 84 to 61) decreased risk of hospital admission for malaria and a 90 [95 CI 3 to 99] decreased risk of severe malaria (severe malarial anemia cerebral malaria or complicated malaria) [70] There was no effect of HbAS on the risk of asymptomatic infec-tions or of parasite density in asymptomatic infections assessed at four cross-sectional surveys There were significant decreases in parasite densities for all of the other categories of infection Additionally in this study unlike another in western Kenya [71] the protection was specific to malaria and did not extend to other common childhood infections including respiratory infections gastroenteritis and helminth infections

What influence the hemoglobinopathic and other polymorphisms may have on the effect of iron sup-plementation on malarial susceptibility is potentially dependent on the extent and mechanisms of protection from infection in the different genotypesmdashinfluences that are likely to be further complicated by differential effects according to age and malarial exposure and effects of coinheritance [72] The coinheritance of the HbS G6PD deficiency and α-thalassemia deletion alle-les is likely to be prevalent in sub-Saharan populations making the study of such effects in real populations extremely difficult by requiring very large sample sizes and complex statistical modeling

To the authorsrsquo knowledge only two published randomized controlled trials of iron supplementation have assessed the effects by genotypemdashin both cases by HbAS versus HbAA [73 74]

In the first trial involving Traditional Birth Attend-ant-administered routine iron supplementation to multigravid Gambian pregnant women Menendez et al [73] reported that although overall there were significant beneficial effects on hemoglobin and packed cell volume (PCV) and on birthweight these effects were entirely accounted for by women with the HbAA phenotype (N = 402 vs N = 98) whereas iron-supplemented HbAS women had lower HB PCV and birthweight than HbAA women receiving placebo Furthermore even in this relatively small study these interactions were statistically significant (p lt 01 for hematological indices at delivery baseline measurements as a covariate p lt 03 for birthweight maternal height included as a covariate) Overall

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S535Iron metabolism and malaria

there was no reported increase in susceptibility to malaria as assessed by the prevalence of peripheral malaria at late pregnancy and delivery or by placental histology Yet iron-supplemented HbAS women had an increased prevalence of placental malaria (76 [2229]) compared with iron-supplemented HbAA women (53 [83158]) placebo-treated HbAA women (59 [91154]) or placebo-treated HbAS women (58 [1933]) At the time of this study IPT prophylaxis was recommended only for primigravid pregnant women in the Gambia hence the choice of the study population What the effects of iron supplementation might be in either primigravidae or multigravidae receiving IPTmdashwhich is now recommended for all pregnant women in malaria-endemic countriesmdashhas not been assessed The protection afforded by the HbAS genotype is likely to vary according to gravidity and malarial endemic-ity In areas of high transmission the majority of the increased risk is borne by primigravidae whereas in areas of lower and highly defined seasonal transmis-sion the increased risk extends to a greater number of pregnancies [75] The protective effect of HbAS is thought to be greatest in relatively nonimmune young children who have not yet developed acquired immunity by exposure to a variety of clonal variants of P falciparum and therefore have not developed a full antibody repertoire to the variant surface antigens (VSA) expressed on the cell surfaces of parasitized red blood cells

In the second trial the effect of the HbAS phenotype on the response to iron supplementation in children was assessed in a subanalysis of a 2 times 2 randomized controlled trial of iron supplementation and inter-mittent preventive treatment (IPT) for malaria using sulfadoxinendashpyrimethamine in anemic Kenyan chil-dren (hemoglobin 7 to 109 gdL) [74] There was no reported increase in the susceptibility to clinical malaria or the prevalence of parasitemia at monthly screening associated with the iron supplementation alone or with IPT [16] whereas IPT plus iron was the most effective in increasing hemoglobin concentrations There were no significant statistical interactions between HbASAA phenotypes and treatment group However there was a nonsignificant increase in the incidence rate ratio of clinical malaria in the HbAS group not receiv-ing IPT during the 12 weeks of follow-up (IRR = 416 95 CI 05 to 346) and increased geometric mean parasite density in both groups but by far the biggest difference was seen in the group receiving IPT (6203 vs 1853 p = 08 for the interaction) The authors acknowledge that the number of clinical events was very small and that these findings would need veri-fication in a larger study since the number of HbAS individuals (approximately 25 to 30) in each treatment group versus approximately 100 HbAA individuals plus the short follow-up time means that the study was grossly underpowered to assess these outcomes If this

effect is real then the age group studied in this trial (2 to 36 months with 78 lt 18 months) should include the most affected although greater effects might be observed in areas of lower transmission and therefore also in a greater age range of children The results of these two trials warrant urgent further trials or retro-spective analysis of prior trials with sufficient power and detail to make firm conclusions on the effects of common polymorphisms on the response to iron sup-plementation which may be expected to vary by age group and transmission intensity

Clinical trials of IPT during infancy (IPTi) have demonstrated a reduction in the prevalence of anemia in young children in malaria-endemic areas [16 18 38 76] and in some trials a reduction in the incidence of clinical malaria [38 76] and morbidity and mortality in the first year of life [38 77] However the effects may vary depending on the timing of dosing choice of drug local levels of resistance and levels of transmission [78 79] On the basis of our analysis above the impact of IPTi plus iron supplementation may be modulated by levels of hemoglobinopathies and therefore suba-nalyses of these studies should be performed according to genotype wherever possible

Interactions of polymorphisms in host iron metabolism and regulatory proteins with malaria

Polymorphisms of haptoglobin a plasma protein that binds free hemoglobin released from lysed red blood cells recirculating the heme portion to the bone marrow through monocyte and macrophage uptake via CD136 have also been associated with malarial outcomes although reports are conflicting Hap-toglobin exists as three common phenotypes Hp1-1 1-2 and 2-2 In case-control studies in India Sudan Ghana and Cameroon the Hp2-2 phenotype has been associated with protection from severe malaria and placental infection [80ndash83] However two studies that have assessed associations with haptoglobin genotypes did not report any associations [84 85] In a cohort study in Gambian children the Hp2-2 genotype was associated with a greater drop in hemoglobin concen-trations across a malarial transmission season [65] The authors proposed that this effect may have been mediated through an increased prevalence of asymp-tomatic infection observed in the Hp2-2 group which contributed to anemia but could provide protection against severe malaria Interestingly similar but smaller drops in hemoglobin concentration were also observed for heterozygotes for G6PD and HbS We are currently analyzing the effects of low-dose iron supplementation during a malarial transmission season in a similar cohort of children

Inducible heme oxygenase (iHO-1) catalyzes the

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S536 A M Prentice et al

breakdown of heme to generate iron carbon monoxide and biliverdin and is expressed in monocytes and mac-rophages among other cells Biliverdin is subsequently degraded to bilirubin which has potent antioxidant effects Microsatellite polymorphisms in the number of tandem repeats in the promoter of iHO-1 have been variously associated with increased and decreased oxidant stress in various disease pathologies However in a case-control study of cerebral malaria patients in Myanmar homozygotes for the short number of repeats (lt 28) previously associated with higher levels of transcription of iHO-1 were significantly more likely to have cerebral malaria than uncomplicated malaria (odds ratio 314 p = 008) [86] It is not clear how this effect may be mediated but it is possible that it results from increased levels of free iron and resulting oxidant stress

In summary the mechanisms by which various genetic polymorphisms interact with malarial infec-tion are still not clear Furthermore it is not clear how they may affect a possible relationship between iron and malaria especially in relation to supplementation which should be differentiated from that of iron status The current evidence suggests that the heterozygous states of the hemoglobinopathies do not protect against malaria by a simple mechanism involving iron with-holding from the pathogen However the effects of iron supplementation in individuals with the most common polymorphisms should be carefully evaluated taking into account differences in transmission intensity and iron status at baseline

Conclusions

The evidence reviewed above tends to substantiate the concerns raised by the recent Pemba trial that universal administration of iron to children in malarious areas may be associated with adverse outcomes The mecha-nism by which this occurs is far from clear and merits

further research to test whether other chemical forms of supplementary iron might carry less risk There is also evidence that the risk profile will be altered by host genetic variations in hemoglobinopathies G6PD and genes regulating iron metabolism However these insights are not of great practical value because population screening and targeted supplementation programs are not feasible in the areas where iron defi-ciency is most prevalent Likewise the evidence that anemic children are probably at low risk for any adverse outcomes associated with iron supplementation implies a need for prescreening that may not be cost-effective or logistically feasible in developing-country settings

The evidence is fairly clear that malaria causes anemia by diverting iron away from bone marrow and erythropoiesis as part of the inflammatory response and hence iron administration alone is not likely to be the most effective means of combating the anemia Other therapeutic paradigms that combat the inflam-mation and adjust the timing of iron administra-tion to children recovering from malaria should be researched

We suggest that further research is still required to confirm the apparent relationships between iron status and malaria and that such studies should also focus on the underlying mechanisms of the putative interaction This might be achieved through the establishment of a multicountry collaboration to standardize protocols both for iron-supplementation interventions and for the assessment of iron and malaria status indicators Standardizing protocols across variations in age groups malaria transmission patterns and genetic distribu-tions of hemoglobinopathies will provide the evidence for a more targeted approach to policies of prevention and treatment of anemia in malaria-endemic regions

Until this evidence is gathered we recommend that iron supplementation in malarious areas must be accompanied by effective systems for ensuring univer-sal rapid access to diagnosis and treatment of malaria or by preventive therapy

References

1 WHO UNICEF Focusing on anaemia Towards an integrated approach for effective anaemia control Joint WHO UNICEF Statement Geneva Joint WHO UNICEF Statement 2004

2 Oppenheimer SJ Iron and its relation to immunity and infectious disease J Nutr 2001131616Sndash33S discussion 33Sndash35S

3 Murray MJ Murray AB Murray NJ Murray MB Diet and cerebral malaria the effect of famine and refeeding Am J Clin Nutr 19783157ndash61

4 Nyakeriga AM Troye-Blomberg M Dorfman JR Alexander ND Back R Kortok M Chemtai AK Marsh K Williams TN Iron deficiency and malaria among children living on the coast of Kenya J Infect Dis 2004 190439ndash47

5 Oppenheimer SJ Macfarlane SB Moody JB Bunari O Hendrickse RG Effect of iron prophylaxis on morbidity due to infectious disease report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 1986 80596ndash602

6 Shipton D Association between haemoglobin level and susceptibility to malaria a study of Gambian children [MSc dissertation] London London School of Hygiene and Tropical Medicine 2004

7 Snow RW Byass P Shenton FC Greenwood BM The relationship between anthropometric measurements and measurements of iron status and susceptibility to malaria in Gambian children Trans R Soc Trop Med Hyg 199185584ndash9

8 Asobayire FS Adou P Davidsson L Cook JD Hurrell

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S537Iron metabolism and malaria

RF Prevalence of iron deficiency with and without concurrent anemia in population groups with high prevalences of malaria and other infections a study in Cote drsquoIvoire Am J Clin Nutr 200174776ndash82

9 Allen SJ OrsquoDonnell A Alexander ND Alpers MP Peto TE Clegg JB Weatherall DJ alpha+-Thalassemia protects children against disease caused by other infec-tions as well as malaria Proc Natl Acad Sci U S A 1997 9414736ndash41

10 Murray MJ Murray AB Murray MB Murray CJ The adverse effect of iron repletion on the course of certain infections Br Med J 197821113ndash5

11 Smith AW Hendrickse RG Harrison C Hayes RJ Greenwood BM The effects on malaria of treatment of iron-deficiency anaemia with oral iron in Gambian children Ann Trop Paediatr 1989917ndash23

12 Oppenheimer SJ Gibson FD Macfarlane SB Moody JB Harrison C Spencer A Bunari O Iron supplementation increases prevalence and effects of malaria report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 198680603ndash12

13 Byles AB Drsquosa A Reduction of reaction due to iron dextran infusion using chloroquine Br Med J 19703625ndash7

14 Berger J Dyck JL Galan P Aplogan A Schneider D Traissac P Hercberg S Effect of daily iron supplementa-tion on iron status cell-mediated immunity and inci-dence of infections in 6ndash36 month old Togolese children Eur J Clin Nutr 20005429ndash35

15 Chippaux JP Schneider D Aplogan A Dyck JL Berger J [Effects of iron supplementation on malaria infection] Bull Soc Pathol Exot 19918454ndash62

16 Desai MR Mei JV Kariuki SK Wannemuehler KA Phil-lips-Howard PA Nahlen BL Kager PA Vulule JM ter Kuile FO Randomized controlled trial of daily iron sup-plementation and intermittent sulfadoxine-pyrimeth-amine for the treatment of mild childhood anemia in western Kenya J Infect Dis 2003187658ndash66

17 Nwanyanwu OC Ziba C Kazembe PN Gamadzi G Gandwe J Redd SC The effect of oral iron therapy during treatment for Plasmodium falciparum malaria with sulphadoxine-pyrimethamine on Malawian chil-dren under 5 years of age Ann Trop Med Parasitol 199690589ndash95

18 Verhoef H West CE Nzyuko SM de Vogel S van der Valk R Wanga MA Kuijsten A Veenemans J Kok FJ Intermittent administration of iron and sulfadoxine-py-rimethamine to control anaemia in Kenyan children a randomised controlled trial Lancet 2002360908ndash14

19 van den Hombergh J Dalderop E Smit Y Does iron therapy benefit children with severe malaria-associated anaemia A clinical trial with 12 weeks supplementation of oral iron in young children from the Turiani Division Tanzania J Trop Pediatr 199642220ndash7

20 Lawless JW Latham MC Stephenson LS Kinoti SN Pertet AM Iron supplementation improves appetite and growth in anemic Kenyan primary school children J Nutr 1994124645ndash54

21 Mebrahtu T Stoltzfus RJ Chwaya HM Jape JK Savioli L Montresor A Albonico M Tielsch JM Low-dose daily iron supplementation for 12 months does not increase the prevalence of malarial infection or den-sity of parasites in young Zanzibari children J Nutr 20041343037ndash41

22 Menendez C Kahigwa E Hirt R Vounatsou P Aponte JJ Font F Acosta CJ Schellenberg DM Galindo CM Kimario J Urassa H Brabin B Smith TA Kitua AY Tanner M Alonso PL Randomised placebo-controlled trial of iron supplementation and malaria chemoproph-ylaxis for prevention of severe anaemia and malaria in Tanzanian infants Lancet 1997350844ndash50

23 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S MrsquoBoge B Greenwood BM The effects of iron supplementation during pregnancy given by traditional birth attendants on the prevalence of anaemia and malaria Trans R Soc Trop Med Hyg 199488590ndash3

24 van Hensbroek MB Morris-Jones S Meisner S Jaffar S Bayo L Dackour R Phillips C Greenwood BM Iron but not folic acid combined with effective antimalarial therapy promotes haematological recovery in African children after acute falciparum malaria Trans R Soc Trop Med Hyg 199589672ndash6

25 Sazawal S Black RE Ramsan M Chwaya HM Stoltzfus RJ Dutta A Dhingra U Kabole I Deb S Othman MK Kabole FM Effects of routine prophylactic supplemen-tation with iron and folic acid on admission to hospital and mortality in preschool children in a high malaria transmission setting community-based randomised placebo-controlled trial Lancet 2006367133ndash43

26 Harvey PW Heywood PF Nesheim MC Galme K Zegans M Habicht JP Stephenson LS Radimer KL Brabin B Forsyth K et al The effect of iron therapy on malarial infection in Papua New Guinean schoolchil-dren Am J Trop Med Hyg 19894012ndash8

27 Andrews NC Iron homeostasis insights from genetics and animal models Nat Rev Genet 20001208ndash17

28 Kristiansen M Graversen JH Jacobsen C Sonne O Hoffman HJ Law SK Moestrup SK Identification of the haemoglobin scavenger receptor Nature 2001409 198ndash201

29 Wickramasinghe SN Abdalla SH Blood and bone marrow changes in malaria Baillieres Best Pract Res Clin Haematol 200013277ndash99

30 Phillips RE Looareesuwan S Warrell DA Lee SH Karbwang J Warrell MJ White NJ Swasdichai C Weatherall DJ The importance of anaemia in cerebral and uncomplicated falciparum malaria role of compli-cations dyserythropoiesis and iron sequestration Q J Med 198658305ndash23

31 Abdalla S Weatherall DJ Wickramasinghe SN Hughes M The anaemia of P falciparum malaria Br J Haematol 198046171ndash83

32 Sen R Bhatnagar BM Singh U Yadav MS Sehgal PK Patterns of erythropoiesis and anaemia in malaria J Commun Dis 199022247ndash53

33 Srichaikul T Wasanasomsithi M Poshyachinda V Panikbutr N Rabieb T Ferrokinetic studies and eryth-ropoiesis in malaria Arch Intern Med 1969124623ndash8

34 Das BS Thurnham DI Das DB Influence of malaria on markers of iron status in children implications for interpreting iron status in malaria-endemic communi-ties Br J Nutr 199778751ndash60

35 Menendez C Quinto LL Kahigwa E Alvarez L Fern-andez R Gimenez N Schellenberg D Aponte JJ Tanner M Alonso PL Effect of malaria on soluble transferrin receptor levels in Tanzanian infants Am J Trop Med Hyg 200165138ndash42

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S538 A M Prentice et al

36 Stoltzfus RJ Chwaya HM Montresor A Albonico M Savioli L Tielsch JM Malaria hookworms and recent fever are related to anemia and iron status indicators in 0- to 5-y old Zanzibari children and these relationships change with age J Nutr 20001301724ndash33

37 Stoltzfus RJ Chwaya HM Albonico M Schulze KJ Savioli L Tielsch JM Serum ferritin erythrocyte pro-toporphyrin and hemoglobin are valid indicators of iron status of school children in a malaria-holoendemic population J Nutr 1997127293ndash8

38 Massaga JJ Kitua AY Lemnge MM Akida JA Malle LN Ronn AM Theander TG Bygbjerg IC Effect of intermittent treatment with amodiaquine on anaemia and malarial fevers in infants in Tanzania a randomised placebo-controlled trial Lancet 20033611853ndash60

39 Verhoef H West CE Kraaijenhagen R Nzyuko SM King R Mbandi MM van Laatum S Hogervorst R Schep C Kok FJ Malarial anemia leads to adequately increased erythropoiesis in asymptomatic Kenyan children Blood 20021003489ndash94

40 Stoltzfus RJ Chway HM Montresor A Tielsch JM Jape JK Albonico M Savioli L Low dose daily iron supplementation improves iron status and appetite but not anemia whereas quarterly anthelminthic treatment improves growth appetite and anemia in Zanzibari preschool children J Nutr 2004134348ndash56

41 Kurtzhals JA Addae MM Akanmori BD Dunyo S Koram KA Appawu MA Nkrumah FK Hviid L Anae-mia caused by asymptomatic Plasmodium falciparum infection in semi-immune African schoolchildren Trans R Soc Trop Med Hyg 199993623ndash7

42 Loyevsky M John C Dickens B Hu V Miller JH Gordeuk VR Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators Mol Biochem Parasitol 199910143ndash59

43 Scholl PF Tripathi AK Sullivan DJ Bioavailable iron and heme metabolism in Plasmodium falciparum Curr Top Microbiol Immunol 2005295293ndash324

44 Darbari D Loyevsky M Gordeuk V Kark JA Castro O Rana S Apprey V Kurantsin-Mills J Fluorescence meas-urements of the labile iron pool of sickle erythrocytes Blood 2003102357ndash64

45 Ginsburg H Iron acquisition by Plasmodium spp Para-sitol Today 199915466

46 Atamna H Ginsburg H Heme degradation in the presence of glutathione A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells J Biol Chem 199527024876ndash83

47 Gabay T Ginsburg H Hemoglobin denaturation and iron release in acidified red blood cell lysatemdasha possible source of iron for intraerythrocytic malaria parasites Exp Parasitol 199377261ndash72

48 Iyer JK Shi L Shankar AH Sullivan DJ Jr Zinc pro-toporphyrin IX binds heme crystals to inhibit the proc-ess of crystallization in Plasmodium falciparum Mol Med 20039175ndash82

49 Cabantchik ZI Moody-Haupt S Gordeuk VR Iron che-lators as anti-infectives malaria as a paradigm FEMS Immunol Med Microbiol 199926289ndash98

50 Hershko C Control of disease by selective iron deple-tion a novel therapeutic strategy utilizing iron chelators Baillieres Clin Haematol 19947965ndash1000

51 Pradines B Tall A Ramiandrasoa F Spiegel A Sokhna C Fusai T Mosnier J Daries W Trape JF Kunesch G Parzy D Rogier C In vitro activity of iron-binding compounds against Senegalese isolates of Plasmodium falciparum J Antimicrob Chemother 2006571093ndash9

52 Meshnick SR Yang YZ Lima V Kuypers F Kam-chonwongpaisan S Yuthavong Y Iron-dependent free radical generation from the antimalarial agent artem-isinin (qinghaosu) Antimicrob Agents Chemother 1993371108ndash14

53 Golenser J Domb A Mordechai-Daniel T Leshem B Luty A Kremsner P Iron chelators correlation between effects on Plasmodium spp and immune functions J Parasitol 200692170ndash7

54 Nyakeriga AM Williams TN Marsh K Wambua S Perlmann H Perlmann P Grandien A Troye-Blomberg M Cytokine mRNA expression and iron status in chil-dren living in a malaria endemic area Scand J Immunol 200561370ndash5

55 Smith HJ Meremikwu M Iron chelating agents for treating malaria Cochrane Database Syst Rev 2003CD001474

56 Weatherall DJ The global problem of genetic disease Ann Hum Biol 200532117ndash22

57 Williams TN Maitland K Bennett S Ganczakowski M Peto TE Newbold CI Bowden DK Weatherall DJ Clegg JB High incidence of malaria in alpha-thalassaemic children Nature 1996383522ndash5

58 Rees DC Williams TN Maitland K Clegg JB Weather-all DJ Alpha thalassaemia is associated with increased soluble transferrin receptor levels Br J Haematol 1998103365ndash9

59 Maitland K Williams TN Bennett S Newbold CI Peto TE Viji J Timothy R Clegg JB Weatherall DJ Bowden DK The interaction between Plasmodium falciparum and P vivax in children on Espiritu Santo island Van-uatu Trans R Soc Trop Med Hyg 199690614ndash20

60 Weatherall DJ Clegg JB Genetic variability in response to infection malaria and after Genes Immun 2002 3331ndash7

61 Parikh S Dorsey G Rosenthal PJ Host polymorphisms and the incidence of malaria in Ugandan children Am J Trop Med Hyg 200471750ndash3

62 Destro Bisol G Genetic resistance to malaria oxidative stress and hemoglobin oxidation Parassitologia 1999 41203ndash4

63 Cappadoro M Giribaldi G OrsquoBrien E Turrini F Mannu F Ulliers D Simula G Luzzatto L Arese P Early phago-cytosis of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes parasitized by Plasmodium falciparum may explain malaria protection in G6PD deficiency Blood 1998922527ndash34

64 Arese P Turrini F Schwarzer E Band 3complement-mediated recognition and removal of normally senes-cent and pathological human erythrocytes Cell Physiol Biochem 200516133ndash46

65 Atkinson SH Rockett K Sirugo G Bejon PA Fulford A OrsquoConnell M A Bailey R Kwiatkowski DP Prentice AM Seasonal Childhood Anaemia in West Africa Is Associated with the Haptoglobin 2-2 Genotype PLoS Med 20063e172

66 Cabrera G Cot M Migot-Nabias F Kremsner PG Deloron P Luty AJ The sickle cell trait is associated

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S539Iron metabolism and malaria

with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens J Infect Dis 20051911631ndash8

67 Williams TN Mwangi TW Roberts DJ Alexander ND Weatherall DJ Wambua S Kortok M Snow RW Marsh K An immune basis for malaria protection by the sickle cell trait PLoS Med 20052e128

68 Ayi K Turrini F Piga A Arese P Enhanced phagocyto-sis of ring-parasitized mutant erythrocytes a common mechanism that may explain protection against falci-parum malaria in sickle trait and beta-thalassemia trait Blood 20041043364ndash71

69 Roberts DJ Harris T Williams T The influence of inherited traits on malaria infection In Bellamy R ed Susceptibility to infectious diseases the importance of host genetics Cambridge Cambridge University Press 2004 139ndash84

70 Williams TN Mwangi TW Wambua S Alexander ND Kortok M Snow RW Marsh K Sickle cell trait and the risk of Plasmodium falciparum malaria and other child-hood diseases J Infect Dis 2005192178ndash86

71 Aidoo M Terlouw DJ Kolczak MS McElroy PD ter Kuile FO Kariuki S Nahlen BL Lal AA Udhayakumar V Protective effects of the sickle cell gene against malaria morbidity and mortality Lancet 20023591311ndash2

72 Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K Nega-tive epistasis between the malaria-protective effects of alpha+-thalassemia and the sickle cell trait Nat Genet 2005371253ndash7

73 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S Ascaso C Smith T MrsquoBoge B Greenwood BM The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS Trans R Soc Trop Med Hyg 199589289ndash92

74 Terlouw DJ Desai MR Wannemuehler KA Kariuki SK Pfeiffer CM Kager PA Shi YP Ter Kuile FO Relation between the response to iron supplementation and sickle cell hemoglobin phenotype in preschool children in western Kenya Am J Clin Nutr 200479466ndash72

75 Duffy PE Fried M Malaria in the pregnant woman Curr Top Microbiol Immunol 2005295169ndash200

76 Schellenberg D Menendez C Kahigwa E Aponte J Vidal J Tanner M Mshinda H Alonso P Intermittent treatment for malaria and anaemia control at time of routine vaccinations in Tanzanian infants a randomised placebo-controlled trial Lancet 20013571471ndash7

77 Schellenberg D Menendez C Aponte JJ Kahigwa E Tanner M Mshinda H Alonso P Intermittent preventive antimalarial treatment for Tanzanian infants follow-up to age 2 years of a randomised placebo-controlled trial Lancet 20053651481ndash3

78 OrsquoMeara WP Breman JG McKenzie FE The promise and potential challenges of intermittent preventive treat-ment for malaria in infants (IPTi) Malar J 2005433

79 White NJ Intermittent presumptive treatment for malaria PLoS Med 20052e3

80 Elagib AA Kider AO Akerstrom B Elbashir MI Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan Trans R Soc Trop Med Hyg 199892309ndash11

81 Minang JT Gyan BA Anchang JK Troye-Blomberg M Perlmann H Achidi EA Haptoglobin phenotypes and malaria infection in pregnant women at delivery in western Cameroon Acta Trop 200490107ndash14

82 Quaye IK Ekuban FA Goka BQ Adabayeri V Kurtzhals JA Gyan B Ankrah NA Hviid L Akanmori BD Hap-toglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria Trans R Soc Trop Med Hyg 200094216ndash9

83 Singh IP Walter H Bhasin MK Bhardwaj V Sudhakar K Genetic markers and malaria Observations in Gujarat India Hum Hered 19863631ndash6

84 Aucan C Walley AJ Greenwood BM Hill AV Hap-toglobin genotypes are not associated with resistance to severe malaria in The Gambia Trans R Soc Trop Med Hyg 200296327ndash8

85 Bienzle U Eggelte TA Adjei LA Dietz E Ehrhardt S Cramer JP Otchwemah RN Mockenhaupt FP Limited influence of haptoglobin genotypes on severe malaria in Ghanaian children Trop Med Int Health 200510668ndash71

86 Takeda M Kikuchi M Ubalee R Na-Bangchang K Ruangweerayut R Shibahara S Imai S Hirayama K Microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with susceptibility to cerebral malaria in Myanmar Jpn J Infect Dis 2005 58268ndash71

87 Shankar AH Nutritional modulation of malaria mor-bidity and mortality J Infect Dis 2000182 Suppl 1 S37ndash53

88 Gera T Sachdev HP Effect of iron supplementation on incidence of infectious illness in children systematic review Bmj 20023251142

Page 5: Iron metabolism and malaria

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S528 A M Prentice et al

Berg

er [

14]

Eur J

Clin

Nut

r 200

06ndash

36 m

o iro

n (2

ndash3

mg

kg ir

on b

atai

n-at

e) v

s pl

aceb

o

N

= 1

97

62

of c

hild

ren

wer

e pa

rasit

emic

at

base

line

Hb

ge 8g

dL

Act

ive

mor

bidi

ty

follo

w-u

p an

d tr

eat-

men

t of a

ll fe

vers

w

ith a

ntim

alar

ials

Prev

alen

ce o

f iro

n-de

ficie

ncy

anem

ia d

ecre

ased

in ir

on

grou

p an

d in

crea

sed

in p

la-

cebo

gro

upA

ll m

arke

rs o

f iro

n st

atus

wer

e sig

nific

antly

hig

her i

n iro

n gr

oup

Incr

ease

in p

erce

ntag

e of

chil-

dren

with

par

asite

mia

gt 3

000

in

iron

gro

up (N

S)

Verh

oef [

18]

Lanc

et 2

002

2ndash36

mo

iron

(6 m

gkg

wk

ferr

ous f

uma-

rate

) vs

SP v

s iro

n +

SP v

s pl

aceb

o

N

= 3

28

Onl

y as

ympt

omat

ic

mal

aria

incl

uded

(3

0 d

ipst

ick

posi-

tive

at b

asel

ine)

Hb

6ndash11

gd

L A

ctiv

e fo

llow

-up

of

feve

rs a

nd tr

eatm

ent

upon

dia

gnos

is

SP a

lone

incr

ease

d H

b by

03

1 g

dLIr

on +

SP

incr

ease

d H

b by

11

1 g

dLIr

on a

lone

incr

ease

d H

b by

10

7 g

dLIn

crea

se in

mal

aria

risk

with

iro

n su

pple

men

tatio

n (N

S)

Des

ai [1

6]J I

nfec

t Dis

2003

2ndash36

mo

IPT

+ iro

n (3

ndash6 m

gkg

ferr

ous

sulfa

te) v

s iro

n vs

IP

T vs

pla

cebo

N

= 5

46

26

of c

hild

ren

wer

e pa

rasit

emic

at b

ase-

line

(are

a of

hig

h IT

N u

se

Hb

7ndash10

9 g

dL

Pass

ive

surv

eil-

lanc

e sy

stem

and

ac

tive

trea

tmen

t of

mal

aria

and

ane

mia

(4

-wee

kly

visit

s)

Iron

gro

up h

ad m

ean

incr

ease

in

Hb

of 0

88g

dL

Ir

on +

IPT

mea

n in

crea

se in

H

b =

114

gd

LIn

crea

se in

mal

aria

par

asite

mia

(N

S) H

R =

114

N

o ef

fect

on

HR

of cl

inic

al

mal

aria

Meb

raht

u [2

1]J N

utr 2

004

4ndash71

mo

iron

(10

mg

ferr

ous s

ulfa

te) v

s iro

n +

meb

enda

zole

vs

meb

enda

zole

+

plac

ebo

vs p

lace

bo

supp

lem

ente

d fo

r 12

mo

N =

614

84

of c

hild

ren

wer

e pa

rasit

emic

at

base

line

94

had

Hb

lt 11

gd

LA

ctiv

e su

rvei

llanc

e no

trea

tmen

tIn

crea

sed

seru

m fe

rriti

nD

ecre

ased

zinc

pro

topo

rphy

rin

in su

pplem

ente

d gr

oup

N

o di

ffere

nce

in m

alar

iom

etric

in

dice

s (pr

eval

ence

or p

ara-

sitem

ia)

but c

linic

al v

alue

s no

t ass

esse

d

Tabl

e 2

Pub

lishe

d tr

ials

of o

ral i

ron

supp

lem

enta

tion

and

mal

aria

risk

Firs

t aut

hor

Sour

ce a

nd y

ear

Stud

y de

sign

Mal

aria

at b

asel

ine

Iron

stat

us in

clus

ion

crite

ria

Cas

e de

tect

ion

and

trea

tmen

t of m

alar

ia

inci

dent

cas

esFi

ndin

gs

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S529Iron metabolism and malaria

partly explain the variations in response to iron supple-mentation reported by different studies other potential complicating factors that contribute to these variations are described in table 4

All but two studies [15 19] have found significant positive effects on markers of iron status in those receiving iron supplementation In the trial of van den Hombergh et al [19] the sample size was limited and baseline characteristics were significantly different between the supplementation and placebo groups Chippaux et al [15] found that anemic children who remained parasite free had increased hemoglobin levels postsupplementation but those that subsequently developed malaria did not The effect of supplementa-tion on hemoglobin concentrations ranged between 06 and 49 gdL with the highest increase occurring in a study that combined iron supplements with anti-malarial therapy [17] Other studies have also shown an additional advantage of iron plus antimalarials as regards hemoglobin recovery [16 18] However despite the hematological benefits all of these studies found nonsignificant increases in adverse malarial outcomes in the groups that received antimalarials plus iron including increased parasite density [16] risk of malaria [18] and treatment failure [17]

Six studies found no effect of iron supplements on malaria risk [19ndash24] of these three included large proportions of anemic subjects (74 to 94) [20 21 24] and one included only children with hemoglobin lt 5 gdL [19] Other studies that stratified by baseline hemoglobin levels [17 25] found that the greatest ben-efits occurred in the most anemic subgroups

Three studies found an increase in clinical malaria attacks in the iron-supplemented groups [10 11 25] and a further six studies found nonsignificant increases in malaria outcomes [14ndash18 26] One of the striking differences between study populations with significant increases in malaria outcomes and those with non-significant effects is access to health care and active treatment of malaria incident cases In fact all but one of the trials [21] that found no effect on malaria outcomes provided access to health care facilities or active follow-up and treatment of malaria incident cases This implies that the potential detrimental effects of iron supplementation may be curtailed by concurrent effective treatment of malaria infections However Verhoef et al and Nwanyanwu et al have shown potential treatment failure effects of combining sulfadoxinendashpyrimethamine with iron in the treatment of preexisting malaria suggesting that antimalarial therapy should precede supplementation [2 17 18]

These observations are further confirmed by a large study in Zanzibar by Sazawal et al [25] that showed increases in malaria-related morbidity and mortality in the iron-supplemented arms of a randomized control-led trial of ironfolate and ironfolate plus zinc versus placebo (summarized in table 2) A subgroup of this Sa

zaw

al[2

5]La

ncet

200

61ndash

35 m

o ir

on (1

25

mg)

+ fo

late

vs

iron

+ fo

late

+ zi

nc v

s pl

aceb

o m

orbi

d-ity

and

mor

talit

y ou

tcom

es a

sses

sed

N

= 3

215

5

43

wer

e pa

rasit

emic

at

bas

elin

eH

b gt

7 g

dL 5

7 o

f ch

ildre

n ha

d H

b lt

10 g

dL

at b

asel

ine

Trea

ted

subs

tudy

chil-

dren

with

clin

ical

m

alar

ia w

ith S

P at

ba

selin

e 6

mo

and

12

mo

Com

bine

d iro

n gr

oups

vs

pla-

cebo

Fo

r adv

erse

mal

aria

-rel

ated

ev

ents

RR

= 1

16

For c

ereb

ral m

alar

ia R

R =

122

Iron

+ fo

late

vs

plac

ebo

For c

ereb

ral m

alar

ia a

s a c

ause

of

dea

th R

R =

17

Subs

tudy

Lo

wer

rate

of a

dver

se e

vent

s in

child

ren

iron

defic

ient

at

base

line

Prot

ectiv

e ef

fect

of i

ron

+ fo

late

in

iron

-def

icie

nt a

nem

ic ch

il-dr

en R

R =

051

Sig

nific

ant d

iffer

ence

s as

repo

rted

by

the

auth

ors

RCT

ran

dom

ized

con

trol

led

tria

l H

b h

emog

lobi

n O

R o

dds

ratio

MC

V m

ean

corp

uscu

lar

volu

me

NS

not

sig

nific

ant

PCV

pac

ked

cell

volu

me

SP

sul

fado

xine

ndashpyr

imet

ham

ine

IPT

inte

rmitt

ent

prev

entiv

e th

erap

y IT

N i

nsec

ticid

e tr

eate

d be

dnet

s ]H

R h

azar

d ra

tio R

R re

lativ

e ris

k

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S530 A M Prentice et al

trial was investigated in more detail and consequently received more intensive diagnosis and treatment of malaria and other infections Substudy children with iron-deficiency anemia at baseline benefited sig-nificantly from iron supplementation in that they had reduced malaria and other infection-related hospital admissions and mortality [25]

The results of this recent study in Zanzibari children have raised new concerns about possible serious side effects of iron supplementation in populations where the etiology of anemia is not solely attributable to iron

deficiency and point to the need for a deeper under-standing of the complex biology of iron sequestration and redistribution between different storage and functional compartments and of the underlying host factors that influence these processes

Effect of malaria on iron metabolism

Erythropoietic iron requirement is met largely through recycling of senescent red blood cells through reticu-loendothelial macrophages where iron is repackaged onto transferrin for transport to the bone marrow [27] Red blood cells are predominantly engulfed directly by reticuloendothelial macrophages however up to 10 of normal recycling occurs as a result of intravascular hemolysis Hemoglobin is released and rapidly bound to haptoglobin and the resultant complex is cleared by liver parenchymal cells or the CD163 macrophagal receptor [28] Malaria-induced destruction of infected and noninfected red blood cells both stresses and impedes the capacity of reticuloendothelial macro-phages to recycle iron back to the bone marrow Intra-vascular rupture of parasitized red cells macrophagal phagocytosis of both parasitized and unparasitized red cells and hypersplenism all contribute to the patho-physiology of the anemia associated particularly with acute malaria

The local epidemiology and transmission character-istics of Plasmodium falciparum together with local drug treatment and intermittent preventive therapy

TABLE 3 Meta-analyses and reviews

First author Sourceyear Study design Findings

Shankar [87] J Infect Dis 2000 Meta-analysis of 13 RCTs of the effect of iron supplementation on malaria and iron status

RR for clinical malaria attack = 11 (NS)RR for slide positive for Plasmodium falci-

parum = 117Absolute increase in infection rate = 57 (NS)RR for spleen enlargement = 112 (NS)Mean increase in Hb = 125 gdLRR for anemia = 05

Oppenheimer [2] J Nutr 2001 Review of controlled interven-tion studies of iron supplemen-tation

Oral iron therapy increased clinical malaria in 5 out of 9 studies

No studies of iron therapy in malarious areas showed benefits on infectious morbidity

Does not report on effect on iron status

Gera [88] BMJ 2002 Systematic review of 28 RCTs of the effect of iron supplementa-tion or fortification in children on infectious illness (including 8 studies of the effect of iron supplementation on malaria)

Pooled OR for malaria-positive smear = 143 but OR when adjusted for baseline malaria smear = 124 (NS)

(The treatment effect increased by 289 times per unit increase in baseline malaria posi-tivity this supports the argument that iron supplementation of children with preexist-ing malaria increases their risk of remaining malaria positive)

Significant differences as reported by the authors RCT randomized controlled trial RR relative risk NS not significant Hb hemoglobin OR odds ratio

TABLE 4 Factors complicating assessment of the relationship between iron status and malaria and the response to iron sup-plementation in malaria-endemic populations

raquo Differences in dose duration and route of iron admin-istration

raquo Degree of malaria immunity in study individuals which can also be related to age and local malaria transmission patterns [7]

raquo Supplementation with iron and folate vs iron alone (especially as some antimalarials have antifolate action) [24]

raquo Markers of iron status used (the confounding effect of infection on serum markers of iron deficiency) [2 8]

raquo Baseline iron status iron-deficient individuals benefit [18 21]

raquo Access to health care and intensity of malaria surveil-lance and treatment during the trial [18 25]

raquo Hemoglobinopathies may affect anemia and response to iron supplementation as well as risk of malaria [9 73]

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S531Iron metabolism and malaria

(IPT) practices influence population immunity and resultant malarial clinical presentation as well as the epidemiology of anemia in a particular setting These factors may also influence the disturbance of iron metabolism and erythropoietic response to iron sup-plementation Acute malaria is associated predomi-nantly with a picture of fever hemolysis and oxidant stress whereas dyserythropoiesis predominates in the anemia of chronic malaria in a semiimmune patient [29] Acute malarial hemolysis represents a major stress on the homeostatic mechanisms of iron flux regulation that have evolved primarily to maintain erythroblast supply while minimizing the oxidant stress-associated effects of iron

Iron can be sequestered and trapped in reticuloen-dothelial macrophages as a result of both chronic and acute malaria and can present a picture of iron-deficient erythropoiesis associated with normal or increased bone marrow iron For instance bone marrow aspirates in 23 Thai patients with uncomplicated acute malaria (age 15 to 52 years) demonstrated malarial pigment in 22 of them Convalescent bone marrow aspirates in 16 patients (3 to 25 days after admission) demonstrated increased iron content compared with the admission sample [30] Five of six Gambian children (lt 5 years of age) with acute malaria had elevated stainable bone marrow iron and four of six children with chronic malaria and severe anemia (hemoglobin lt 6 gdL) had either normal or markedly increased levels of bone marrow stainable iron [31] Eighty-six percent of Indian children and adults (N = 26) with acute and 84 of those with chronic falciparum malaria and anemia (mean hemoglobin 54 gdL N = 38) had normal or increased bone marrow iron stores [32] Ferrokinetic studies involving the intravenous administration of 59Fe demonstrated low unsaturated iron-binding capacity and a rapid plasma iron disappearance time in both parasitemic and postparasitemic patients with acute and secondary (recent acute infection with persistent parasitemia) P falciparum and P vivax in Thai adults compared with controls [33] Incorporation of 59Fe into red blood cells was decreased in acute (N = 5) and secondary parasitemia (11 of 14) but found to be largely normal in the postparasitemic patients includ-ing 3 who were restudied from the parasitemic group Iron sequestration in acute malaria is cytokine driven (elevated tumor necrosis factor α [TNF-α] ILndash1 and interferon γ [IFN-γ] and diminished ILndash10) [29] prob-ably mediated via hepcidin however quantifying this phenomenon assessing how long it persists after acute malaria and in association with chronic malaria and assessing its importance in relation to malarial anemia malaria-associated immunosuppression and response to iron supplementation is difficult since there are few data Conventional indices of iron storage (eg ferritin) or of tissue supply (eg zinc protoporphyrin soluble transferrin receptor transferrin saturation) are

affected by inflammation [8 34ndash36] and the assess-ment of the iron status of young children in malarious areas with acute or chronic malaria is problematic [34] In a holoendemic environment ferritin and eryth-rocyte protoporphyrin were not affected by chronic malaria in older children [37] These indices also do not distinguish between iron deficiency and iron sequestration

Effect of malaria on response to iron supplementation

Malaria-induced anemia does not lead to loss of iron from the body However iron deficiency often coex-ists with malaria in areas of malaria transmission and therapy for severe postmalarial anemia commonly assumes a component due to preexisting iron defi-ciency Iron supplements are routinely prescribed both for severe malaria-associated anemia and for presumed iron-deficient anemia in a malaria-endemic environ-ment Few studies however have looked at the effect of acute malaria on the response to iron supplementation and even fewer have addressed the effect of chronic asymptomatic malaria More commonly studies either have either assessed the response to supplementation of children with anemia of undefined etiology in areas of coexistent malaria iron deficiency and hookworm or have randomized children who were anemic after malaria to a variety of hematinics In a study of 222 Malawian children (lt 5 years of age) with anemia after acute malaria the use of Fansidar and daily supplemen-tal iron resulted in a significantly greater hemoglobin recovery than Fansidar alone or Fansidar and weekly iron only in those children with initial hemoglobin between 5 and 8 gdL [17] However a larger propor-tion of the iron-treated children failed to clear their malaria In the Gambia 600 children (mean age 52 months mean hemoglobin 96 gdL) with uncompli-cated falciparum malaria randomized to receive chlo-roquine or Fansidar as treatment and then either iron folic acid or placebo for 28 days [22] demonstrated a significantly better hemoglobin response with iron than with placebo or folic acid (the difference in mean hemoglobin level after 1 month was 07 gdL) One hundred Tanzanian children (lt 30 months of age) with severe anemia (hemoglobin lt 5 gdL) were randomized either to receive daily iron supplementation or to be controls after antimalarial treatment [19] Among the 60 who completed the 12-week follow-up without a transfusion (30 in each group) there were no differ-ences in hemoglobin recovery From these studies the role of iron supplementation in the treatment of anemia after acute malaria is unclear and it is likely that the hemoglobin response to supplementation is influenced by both the direct inflammatory effect of malaria on iron absorption and utilization and preexistent iron

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S532 A M Prentice et al

deficiency which is impossible to assess in the presence of malaria In the Gambia we recently compared the absorption of stable-isotope-labeled iron in children anemic as a result of iron deficiency and children anemic after acute malaria Both groups were given 30 days of iron supplementation and the malaria group demonstrated significantly better hemoglobin recovery despite initially significantly reduced iron absorption (Doherty et al unpublished results) Utilization of sequestered iron is likely to be a major contributor to erythroblastic iron requirement after acute malaria

Studies of iron supplementation of populations of anemic children in malarious areas have reported either improved hemoglobin response or decreased prevalence of severe anemia [16 22 38 39] Incorpo-ration of antimalarial intervention arms is common Malaria transmission characteristics study design use of antecedent antimalarials differing iron supplemen-tation doses and differing outcome measures as well as different prevalence rates of iron deficiency and hook-worm infection have made the assessment of factors affecting hemoglobin response to iron supplementation difficult In particular the effect of chronic malaria on response to supplementation in high-transmission areas is unclear as the etiology of the anemia and the chronicity of malaria parasitemia are often undefined in study subjects In an area of intense transmission in Tanzania in which more than 80 of children (4 to 71 months old) were parasitemic at baseline and where malaria infection was strongly associated with hemo-globin supplementation improved the iron status and motor and language development of an iron-deficient population but not did not improve hemoglobin [21 36 40] The authors concluded that factors including malarial parasitemia or ineffective erythropoiesis due to inflammatory processes in a population with high levels of infectious morbidity and inflammation might have limited erythropoiesis

An inflammatory-mediated block to iron absorp-tion and utilization is likely to limit the erythropoietic response to supplemental iron after acute malaria how-ever it is unclear whether chronic parasitemia similarly limits the response to supplemental iron The asso-ciation of chronic malaria with anemia [39] stainable bone marrow iron [34] and increased cytokine levels [41] might suggest a probable effect and the eradica-tion of parasites has been associated with hemoglobin improvement without supplemental iron [31]

Iron metabolism by malaria parasites

In this section we consider whether the availability of iron in the host could modulate the efficiency with which malaria parasites can establish an infection and the severity of that infection What evidence is there to support the ldquonutritional immunityrdquo hypothesis that

host iron availability could limit parasite invasion or multiplication andor the clinical sequelae of para-site infection Support for the nutritional immunity hypothesis first stated in the 1970s has generally waned for the majority of pathogens [2] but there may still be a case for obligate intracellular pathogensmdashincluding Plasmodium spp

It may be informative to examine the research of other scientists than those typically involved in the cur-rent debate For example in order for this hypothesis to be truemdashat least in terms of the success of parasite invasion and replicationmdashit is a requirement that P falciparum be dependent on host iron sources for its survival Next is iron deficiency ever likely to be a limiting factor in the supply of iron to the parasite The most recent research suggests that P falciparum does utilize iron from the host but not from the abundant supplies available in erythrocyte hemoglobin the heme portion of which is quickly degraded to nontoxic but non-iron-bioavailable hemozoin or from the plasma via transferrin but from another source possibly an intraerythrocytic labile pool of ferrous iron [42 43] Interestingly measurements of this labile ferrous iron in normal and sickled erythrocytes indicate it to be positively associated with hemoglobin concentrations and negatively associated with plasma ferritin [44] However other researchers have reported evidence to suggest that the degradation of heme to hemozoin is incomplete and that 50 of heme may be degraded via an alternative pathway involving reduced glutathione and releasing bioavailable iron [45 46] As it has been estimated that less than 1 of heme iron would be sufficient to meet parasite iron requirements [47] iron deficiency would never induce iron-limited growth if hemoglobin were the iron source for parasites

Another mechanism by which iron deficiency may limit parasite growth is that proposed recently by Iyer et al [48] who demonstrated the inhibition of hemozoin formation from toxic free heme by the naturally occur-ring zinc protoporphyrin IX (ZPP) at levels likely to be encountered in anemic erythrocytes It is interesting to note that this is thought to be the mechanism by which the quinoline antimalarials act Furthermore Iyer et al demonstrated that quinolines competed for ZPP bind-ing and prevention of hemozoin formation It is pos-sible that via this mechanism moderate anemia could allow the persistence of low levels of parasitemia and therefore affect the development of exposure-related antibody repertoire and clinical immunitymdashwith consequent effects on future malarial incidence and malaria-associated anemia However the evidence for such an effect in human populations is currently limited due to the lack of longitudinal studies assessing ZPP levels and parasite prevalence and density from infancy onwards

Another research area that has been used to support the hypothesis of decreased iron availability is that

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S533Iron metabolism and malaria

of the effects of iron chelators on parasite growth in vitro and in vivo [49 50] Furthermore some antima-larial drugs such as the antibiotic cyclines including doxycycline are also iron chelators However iron chelators may not be acting by depriving the parasite of iron Alternative mechanisms have been suggested for some chelators including the induction of reactive oxygen species from dissociation of iron from heme and hemozoin as suggested for the lipophilic FR160 [51] similar to the suggested mechanism of artemisinin [52] Furthermore differences between the efficacy of chelators in vitro and in vivo have been associated with differences in immune modulation [53] This may suggest that iron status could affect malarial outcomes via direct effects on immune modulation as suggested by Nyakeriga et al [54] The evidence base for the effects of current iron-chelator therapies in reducing the prevalence density or clinical sequelae of malaria is weakmdashas outlined in a recent Cochrane review of clinical trials involving the use of either desferioxamine or the orally available deferiprone [55] in which all of the seven studies included had limitations relat-ing to study size relevance of study populations and more critically methodological and analytical faults However the authors of this review concluded that the results suggested possible benefits of treatment in cerebral malaria with a shorter recovery time from coma and decreased time to parasite clearance The initial justification for using iron-chelator therapy in cerebral malaria was based on the premise of prevent-ing iron-induced damage to brain cells resulting from hemolysis Therefore it is important to note that the possible benefits of iron-chelator therapy may not relate to limitation of iron for parasite growth and may there-fore not provide evidence in support of the nutritional immunity hypothesis

Iron malaria and hemoglobinopathies

How do hemoglobinopathies protect against parasite invasion or multiplication andor clinical sequelae of parasite infection Are these polymorphisms likely to affect the relationship between iron status or supple-mentation and malaria

J B S Haldane is credited with first postulat-ing heterozygote selection as an explanation for the high prevalence of the thalassemias and later other hemoglobinopathies He suggested that the small size reduced hemoglobin concentrations and increased resistance to hypertonic solutions of such cells may result in decreased parasite invasion or growth Although this hypothesis has been widely accepted for some time it has only recently been possible to dem-onstrate that these mutations have been maintained by selection mostly by malaria but possibly also other infectious causes However the extent and mechanisms

of protection are still debated At least in vitro many studies have failed to demonstrate decreased ability of parasites to invade or grow in thalassemic cells or cells containing hemoglobin S (HbS) Instead the mecha-nisms appear to be more complicated and possibly to vary between local conditions

The common polymorphisms involved in hemo-globin synthesis or red cell formation include sickle hemoglobin (HbS) HbC and HbE the α and β-thalassemias and South Asian ovalocytosis The geographic distribution of these varies across tropi-cal areas and can vary extensively even within closely related regions Current estimates of these polymor-phisms are often based on single sites and are likely to be underestimates [56] but a figure of 27 million carriers of the main hemoglobinopathies has been proposed [56] The carrier frequency for HbS is esti-mated at between 5 and 40 in populations across sub-Saharan Africa the Middle East and parts of South Asia HbC is limited to parts of West and North Africa whereas HbE is common in some parts of India and Southeast Asia with carrier rates up to 60 The thalassemias have the broadest geographic distribution and also the widest range of causative mutations and clinical outcomes The carrier frequencies for the more severe range of β-thalassemias is generally lower than for the α-thalassemias which are estimated to reach carrier frequencies of up to 20 in sub-Saharan Africa higher in Middle Eastern and Indian populations and up to 80 in some Pacific populations (reviewed in Williams et al [57] Rees et al [58] and Maitland et al [59])

In β-thalassemias excess α-globin chains precipitate in red cell precursors leading to ineffective erythropoi-esis and resulting in anemia in the context of increased iron absorption and iron accumulation The clinical expression of β-thalassemia varies widely depending on the exact genetic lesions inherited and interactions with other genetic loci including the α and γ globin genes β-Thalassemia trait and β-thalassemia interme-diate are often asymptomatic and may not be diagnosed except for mild anemia In α-thalassemia the excess β-chains form stable homotetramers which do not sig-nificantly affect erythropoiesis but cause an increased rate of hemolysis of mature cells The degree of the deficit of α-globin chains depends on the number of α-globin genes inactivated and unless three α-globin genes are lost the effects are subtle and various so that the condition will go largely undiagnosed It might be supposed that iron supplementation could be more deleterious in populations with a high prevalence of β-thalassemia mutations because of the inability to utilize the iron leading to increased iron availability to pathogens or iron-induced oxidant stress Interest-ingly Oppenheimer [2] reported that the increased susceptibility to malaria associated with parenteral iron in Papua New Guinean children was not apparent in

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S534 A M Prentice et al

single-deletion α-thalassemia compared with normal children

In a prospective casendashcontrol study in Papua New Guinea α-thalassemic α+ndash homozygotes and α+ndash heterozygotes had a greatly decreased risk of severe malaria (incidence rate ratio = 04 and 066) compared with controls [9] Furthermore protection was also observed for hospitalization from other infections possibly suggesting an immune component to the pro-tection [60] although the reduction of severe malaria may reduce infectious sequelae by invasive bacte-rial disease In apparent contrast α-thalassemia has also been associated with an increased prevalence of uncomplicated malaria in Vanuatu particularly in very young children with P vivax [57] It was suggested that increased red cell turnover in these children increased susceptibility to P vivax [58] resulting in cross-species immunity to P falciparum in later life [59] A similar finding was reported for glucose-6-phosphate dehy-drogenase (G6PD) deficiency in a cohort study in Uganda in which many other potential risk factors for malarial infection were controlled for (age water source use of prophylaxis bednet usage and proxim-ity to mosquito breeding sites) Female heterozygotes for G6PD had a significantly increased incidence of uncomplicated malaria (IRR = 13 p = 03) and a trend for increased parasite densities similar trends were seen for hemizygote males This was different from the pattern observed for HbS heterozygotes who had a nonsignificantly decreased incidence of uncomplicated malaria and decreased parasite densities [61]

A mechanism that has been suggested for G6PD defi-ciency and that may also be applicable to sickle (HbAS) and thalassemic cells involves decreased oxidative protection (G6PD) or increased constitutive oxidative stress of these cells (HbAS αβ thalassemias) especially when infected resulting in increased clearance of the cells from non-malaria-specific immune mechanisms essentially the same as the normal removal of old ldquosenescentrdquo red cells by phagocytes [62ndash64] It has been proposed that such a mechanism could prevent parasitemias from reaching critically high densities and therefore protect from severe malaria and also facilitate the development of antibody repertoires in children from the maintenance of low-grade infections in young children [65ndash67] In a slight modification of this hypothesis the increased phagocytic removal of early ring-stage infected cellsmdashcompared with schizonts and trophozoitesmdashhas been demonstrated for G6PD β-thalassemic and HbAS cells in vitro but not for α-thalassemic infected cells [68] The phagocytosis of ring compared with later stages may be advantageous since rings contain less hemozoin the buildup of which in monocytes has been associated with decreased func-tion Additionally the reduction of the later stages of parasite development may reduce the development of severe symptoms such as cerebral malaria from

reduced endothelial adhesion of late-stage infected red blood cells to receptors such as intracellular adhesion molecule-1 (ICAM-1)

The epidemiological evidence for a protective effect of HbAS suggests that the protective effects are great-est for severe disease (reviewed by Roberts et al [69]) In the most comprehensive study to date a detailed prospective cohort in two Kenyan populations it was reported that HbS heterozygotes had a significantly decreased risk of mild clinical malaria as assessed by active surveillance (50 decreased risk 95 confi-dence interval [CI] 26 to 67]) a 75 (95 CI 84 to 61) decreased risk of hospital admission for malaria and a 90 [95 CI 3 to 99] decreased risk of severe malaria (severe malarial anemia cerebral malaria or complicated malaria) [70] There was no effect of HbAS on the risk of asymptomatic infec-tions or of parasite density in asymptomatic infections assessed at four cross-sectional surveys There were significant decreases in parasite densities for all of the other categories of infection Additionally in this study unlike another in western Kenya [71] the protection was specific to malaria and did not extend to other common childhood infections including respiratory infections gastroenteritis and helminth infections

What influence the hemoglobinopathic and other polymorphisms may have on the effect of iron sup-plementation on malarial susceptibility is potentially dependent on the extent and mechanisms of protection from infection in the different genotypesmdashinfluences that are likely to be further complicated by differential effects according to age and malarial exposure and effects of coinheritance [72] The coinheritance of the HbS G6PD deficiency and α-thalassemia deletion alle-les is likely to be prevalent in sub-Saharan populations making the study of such effects in real populations extremely difficult by requiring very large sample sizes and complex statistical modeling

To the authorsrsquo knowledge only two published randomized controlled trials of iron supplementation have assessed the effects by genotypemdashin both cases by HbAS versus HbAA [73 74]

In the first trial involving Traditional Birth Attend-ant-administered routine iron supplementation to multigravid Gambian pregnant women Menendez et al [73] reported that although overall there were significant beneficial effects on hemoglobin and packed cell volume (PCV) and on birthweight these effects were entirely accounted for by women with the HbAA phenotype (N = 402 vs N = 98) whereas iron-supplemented HbAS women had lower HB PCV and birthweight than HbAA women receiving placebo Furthermore even in this relatively small study these interactions were statistically significant (p lt 01 for hematological indices at delivery baseline measurements as a covariate p lt 03 for birthweight maternal height included as a covariate) Overall

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S535Iron metabolism and malaria

there was no reported increase in susceptibility to malaria as assessed by the prevalence of peripheral malaria at late pregnancy and delivery or by placental histology Yet iron-supplemented HbAS women had an increased prevalence of placental malaria (76 [2229]) compared with iron-supplemented HbAA women (53 [83158]) placebo-treated HbAA women (59 [91154]) or placebo-treated HbAS women (58 [1933]) At the time of this study IPT prophylaxis was recommended only for primigravid pregnant women in the Gambia hence the choice of the study population What the effects of iron supplementation might be in either primigravidae or multigravidae receiving IPTmdashwhich is now recommended for all pregnant women in malaria-endemic countriesmdashhas not been assessed The protection afforded by the HbAS genotype is likely to vary according to gravidity and malarial endemic-ity In areas of high transmission the majority of the increased risk is borne by primigravidae whereas in areas of lower and highly defined seasonal transmis-sion the increased risk extends to a greater number of pregnancies [75] The protective effect of HbAS is thought to be greatest in relatively nonimmune young children who have not yet developed acquired immunity by exposure to a variety of clonal variants of P falciparum and therefore have not developed a full antibody repertoire to the variant surface antigens (VSA) expressed on the cell surfaces of parasitized red blood cells

In the second trial the effect of the HbAS phenotype on the response to iron supplementation in children was assessed in a subanalysis of a 2 times 2 randomized controlled trial of iron supplementation and inter-mittent preventive treatment (IPT) for malaria using sulfadoxinendashpyrimethamine in anemic Kenyan chil-dren (hemoglobin 7 to 109 gdL) [74] There was no reported increase in the susceptibility to clinical malaria or the prevalence of parasitemia at monthly screening associated with the iron supplementation alone or with IPT [16] whereas IPT plus iron was the most effective in increasing hemoglobin concentrations There were no significant statistical interactions between HbASAA phenotypes and treatment group However there was a nonsignificant increase in the incidence rate ratio of clinical malaria in the HbAS group not receiv-ing IPT during the 12 weeks of follow-up (IRR = 416 95 CI 05 to 346) and increased geometric mean parasite density in both groups but by far the biggest difference was seen in the group receiving IPT (6203 vs 1853 p = 08 for the interaction) The authors acknowledge that the number of clinical events was very small and that these findings would need veri-fication in a larger study since the number of HbAS individuals (approximately 25 to 30) in each treatment group versus approximately 100 HbAA individuals plus the short follow-up time means that the study was grossly underpowered to assess these outcomes If this

effect is real then the age group studied in this trial (2 to 36 months with 78 lt 18 months) should include the most affected although greater effects might be observed in areas of lower transmission and therefore also in a greater age range of children The results of these two trials warrant urgent further trials or retro-spective analysis of prior trials with sufficient power and detail to make firm conclusions on the effects of common polymorphisms on the response to iron sup-plementation which may be expected to vary by age group and transmission intensity

Clinical trials of IPT during infancy (IPTi) have demonstrated a reduction in the prevalence of anemia in young children in malaria-endemic areas [16 18 38 76] and in some trials a reduction in the incidence of clinical malaria [38 76] and morbidity and mortality in the first year of life [38 77] However the effects may vary depending on the timing of dosing choice of drug local levels of resistance and levels of transmission [78 79] On the basis of our analysis above the impact of IPTi plus iron supplementation may be modulated by levels of hemoglobinopathies and therefore suba-nalyses of these studies should be performed according to genotype wherever possible

Interactions of polymorphisms in host iron metabolism and regulatory proteins with malaria

Polymorphisms of haptoglobin a plasma protein that binds free hemoglobin released from lysed red blood cells recirculating the heme portion to the bone marrow through monocyte and macrophage uptake via CD136 have also been associated with malarial outcomes although reports are conflicting Hap-toglobin exists as three common phenotypes Hp1-1 1-2 and 2-2 In case-control studies in India Sudan Ghana and Cameroon the Hp2-2 phenotype has been associated with protection from severe malaria and placental infection [80ndash83] However two studies that have assessed associations with haptoglobin genotypes did not report any associations [84 85] In a cohort study in Gambian children the Hp2-2 genotype was associated with a greater drop in hemoglobin concen-trations across a malarial transmission season [65] The authors proposed that this effect may have been mediated through an increased prevalence of asymp-tomatic infection observed in the Hp2-2 group which contributed to anemia but could provide protection against severe malaria Interestingly similar but smaller drops in hemoglobin concentration were also observed for heterozygotes for G6PD and HbS We are currently analyzing the effects of low-dose iron supplementation during a malarial transmission season in a similar cohort of children

Inducible heme oxygenase (iHO-1) catalyzes the

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S536 A M Prentice et al

breakdown of heme to generate iron carbon monoxide and biliverdin and is expressed in monocytes and mac-rophages among other cells Biliverdin is subsequently degraded to bilirubin which has potent antioxidant effects Microsatellite polymorphisms in the number of tandem repeats in the promoter of iHO-1 have been variously associated with increased and decreased oxidant stress in various disease pathologies However in a case-control study of cerebral malaria patients in Myanmar homozygotes for the short number of repeats (lt 28) previously associated with higher levels of transcription of iHO-1 were significantly more likely to have cerebral malaria than uncomplicated malaria (odds ratio 314 p = 008) [86] It is not clear how this effect may be mediated but it is possible that it results from increased levels of free iron and resulting oxidant stress

In summary the mechanisms by which various genetic polymorphisms interact with malarial infec-tion are still not clear Furthermore it is not clear how they may affect a possible relationship between iron and malaria especially in relation to supplementation which should be differentiated from that of iron status The current evidence suggests that the heterozygous states of the hemoglobinopathies do not protect against malaria by a simple mechanism involving iron with-holding from the pathogen However the effects of iron supplementation in individuals with the most common polymorphisms should be carefully evaluated taking into account differences in transmission intensity and iron status at baseline

Conclusions

The evidence reviewed above tends to substantiate the concerns raised by the recent Pemba trial that universal administration of iron to children in malarious areas may be associated with adverse outcomes The mecha-nism by which this occurs is far from clear and merits

further research to test whether other chemical forms of supplementary iron might carry less risk There is also evidence that the risk profile will be altered by host genetic variations in hemoglobinopathies G6PD and genes regulating iron metabolism However these insights are not of great practical value because population screening and targeted supplementation programs are not feasible in the areas where iron defi-ciency is most prevalent Likewise the evidence that anemic children are probably at low risk for any adverse outcomes associated with iron supplementation implies a need for prescreening that may not be cost-effective or logistically feasible in developing-country settings

The evidence is fairly clear that malaria causes anemia by diverting iron away from bone marrow and erythropoiesis as part of the inflammatory response and hence iron administration alone is not likely to be the most effective means of combating the anemia Other therapeutic paradigms that combat the inflam-mation and adjust the timing of iron administra-tion to children recovering from malaria should be researched

We suggest that further research is still required to confirm the apparent relationships between iron status and malaria and that such studies should also focus on the underlying mechanisms of the putative interaction This might be achieved through the establishment of a multicountry collaboration to standardize protocols both for iron-supplementation interventions and for the assessment of iron and malaria status indicators Standardizing protocols across variations in age groups malaria transmission patterns and genetic distribu-tions of hemoglobinopathies will provide the evidence for a more targeted approach to policies of prevention and treatment of anemia in malaria-endemic regions

Until this evidence is gathered we recommend that iron supplementation in malarious areas must be accompanied by effective systems for ensuring univer-sal rapid access to diagnosis and treatment of malaria or by preventive therapy

References

1 WHO UNICEF Focusing on anaemia Towards an integrated approach for effective anaemia control Joint WHO UNICEF Statement Geneva Joint WHO UNICEF Statement 2004

2 Oppenheimer SJ Iron and its relation to immunity and infectious disease J Nutr 2001131616Sndash33S discussion 33Sndash35S

3 Murray MJ Murray AB Murray NJ Murray MB Diet and cerebral malaria the effect of famine and refeeding Am J Clin Nutr 19783157ndash61

4 Nyakeriga AM Troye-Blomberg M Dorfman JR Alexander ND Back R Kortok M Chemtai AK Marsh K Williams TN Iron deficiency and malaria among children living on the coast of Kenya J Infect Dis 2004 190439ndash47

5 Oppenheimer SJ Macfarlane SB Moody JB Bunari O Hendrickse RG Effect of iron prophylaxis on morbidity due to infectious disease report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 1986 80596ndash602

6 Shipton D Association between haemoglobin level and susceptibility to malaria a study of Gambian children [MSc dissertation] London London School of Hygiene and Tropical Medicine 2004

7 Snow RW Byass P Shenton FC Greenwood BM The relationship between anthropometric measurements and measurements of iron status and susceptibility to malaria in Gambian children Trans R Soc Trop Med Hyg 199185584ndash9

8 Asobayire FS Adou P Davidsson L Cook JD Hurrell

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S537Iron metabolism and malaria

RF Prevalence of iron deficiency with and without concurrent anemia in population groups with high prevalences of malaria and other infections a study in Cote drsquoIvoire Am J Clin Nutr 200174776ndash82

9 Allen SJ OrsquoDonnell A Alexander ND Alpers MP Peto TE Clegg JB Weatherall DJ alpha+-Thalassemia protects children against disease caused by other infec-tions as well as malaria Proc Natl Acad Sci U S A 1997 9414736ndash41

10 Murray MJ Murray AB Murray MB Murray CJ The adverse effect of iron repletion on the course of certain infections Br Med J 197821113ndash5

11 Smith AW Hendrickse RG Harrison C Hayes RJ Greenwood BM The effects on malaria of treatment of iron-deficiency anaemia with oral iron in Gambian children Ann Trop Paediatr 1989917ndash23

12 Oppenheimer SJ Gibson FD Macfarlane SB Moody JB Harrison C Spencer A Bunari O Iron supplementation increases prevalence and effects of malaria report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 198680603ndash12

13 Byles AB Drsquosa A Reduction of reaction due to iron dextran infusion using chloroquine Br Med J 19703625ndash7

14 Berger J Dyck JL Galan P Aplogan A Schneider D Traissac P Hercberg S Effect of daily iron supplementa-tion on iron status cell-mediated immunity and inci-dence of infections in 6ndash36 month old Togolese children Eur J Clin Nutr 20005429ndash35

15 Chippaux JP Schneider D Aplogan A Dyck JL Berger J [Effects of iron supplementation on malaria infection] Bull Soc Pathol Exot 19918454ndash62

16 Desai MR Mei JV Kariuki SK Wannemuehler KA Phil-lips-Howard PA Nahlen BL Kager PA Vulule JM ter Kuile FO Randomized controlled trial of daily iron sup-plementation and intermittent sulfadoxine-pyrimeth-amine for the treatment of mild childhood anemia in western Kenya J Infect Dis 2003187658ndash66

17 Nwanyanwu OC Ziba C Kazembe PN Gamadzi G Gandwe J Redd SC The effect of oral iron therapy during treatment for Plasmodium falciparum malaria with sulphadoxine-pyrimethamine on Malawian chil-dren under 5 years of age Ann Trop Med Parasitol 199690589ndash95

18 Verhoef H West CE Nzyuko SM de Vogel S van der Valk R Wanga MA Kuijsten A Veenemans J Kok FJ Intermittent administration of iron and sulfadoxine-py-rimethamine to control anaemia in Kenyan children a randomised controlled trial Lancet 2002360908ndash14

19 van den Hombergh J Dalderop E Smit Y Does iron therapy benefit children with severe malaria-associated anaemia A clinical trial with 12 weeks supplementation of oral iron in young children from the Turiani Division Tanzania J Trop Pediatr 199642220ndash7

20 Lawless JW Latham MC Stephenson LS Kinoti SN Pertet AM Iron supplementation improves appetite and growth in anemic Kenyan primary school children J Nutr 1994124645ndash54

21 Mebrahtu T Stoltzfus RJ Chwaya HM Jape JK Savioli L Montresor A Albonico M Tielsch JM Low-dose daily iron supplementation for 12 months does not increase the prevalence of malarial infection or den-sity of parasites in young Zanzibari children J Nutr 20041343037ndash41

22 Menendez C Kahigwa E Hirt R Vounatsou P Aponte JJ Font F Acosta CJ Schellenberg DM Galindo CM Kimario J Urassa H Brabin B Smith TA Kitua AY Tanner M Alonso PL Randomised placebo-controlled trial of iron supplementation and malaria chemoproph-ylaxis for prevention of severe anaemia and malaria in Tanzanian infants Lancet 1997350844ndash50

23 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S MrsquoBoge B Greenwood BM The effects of iron supplementation during pregnancy given by traditional birth attendants on the prevalence of anaemia and malaria Trans R Soc Trop Med Hyg 199488590ndash3

24 van Hensbroek MB Morris-Jones S Meisner S Jaffar S Bayo L Dackour R Phillips C Greenwood BM Iron but not folic acid combined with effective antimalarial therapy promotes haematological recovery in African children after acute falciparum malaria Trans R Soc Trop Med Hyg 199589672ndash6

25 Sazawal S Black RE Ramsan M Chwaya HM Stoltzfus RJ Dutta A Dhingra U Kabole I Deb S Othman MK Kabole FM Effects of routine prophylactic supplemen-tation with iron and folic acid on admission to hospital and mortality in preschool children in a high malaria transmission setting community-based randomised placebo-controlled trial Lancet 2006367133ndash43

26 Harvey PW Heywood PF Nesheim MC Galme K Zegans M Habicht JP Stephenson LS Radimer KL Brabin B Forsyth K et al The effect of iron therapy on malarial infection in Papua New Guinean schoolchil-dren Am J Trop Med Hyg 19894012ndash8

27 Andrews NC Iron homeostasis insights from genetics and animal models Nat Rev Genet 20001208ndash17

28 Kristiansen M Graversen JH Jacobsen C Sonne O Hoffman HJ Law SK Moestrup SK Identification of the haemoglobin scavenger receptor Nature 2001409 198ndash201

29 Wickramasinghe SN Abdalla SH Blood and bone marrow changes in malaria Baillieres Best Pract Res Clin Haematol 200013277ndash99

30 Phillips RE Looareesuwan S Warrell DA Lee SH Karbwang J Warrell MJ White NJ Swasdichai C Weatherall DJ The importance of anaemia in cerebral and uncomplicated falciparum malaria role of compli-cations dyserythropoiesis and iron sequestration Q J Med 198658305ndash23

31 Abdalla S Weatherall DJ Wickramasinghe SN Hughes M The anaemia of P falciparum malaria Br J Haematol 198046171ndash83

32 Sen R Bhatnagar BM Singh U Yadav MS Sehgal PK Patterns of erythropoiesis and anaemia in malaria J Commun Dis 199022247ndash53

33 Srichaikul T Wasanasomsithi M Poshyachinda V Panikbutr N Rabieb T Ferrokinetic studies and eryth-ropoiesis in malaria Arch Intern Med 1969124623ndash8

34 Das BS Thurnham DI Das DB Influence of malaria on markers of iron status in children implications for interpreting iron status in malaria-endemic communi-ties Br J Nutr 199778751ndash60

35 Menendez C Quinto LL Kahigwa E Alvarez L Fern-andez R Gimenez N Schellenberg D Aponte JJ Tanner M Alonso PL Effect of malaria on soluble transferrin receptor levels in Tanzanian infants Am J Trop Med Hyg 200165138ndash42

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S538 A M Prentice et al

36 Stoltzfus RJ Chwaya HM Montresor A Albonico M Savioli L Tielsch JM Malaria hookworms and recent fever are related to anemia and iron status indicators in 0- to 5-y old Zanzibari children and these relationships change with age J Nutr 20001301724ndash33

37 Stoltzfus RJ Chwaya HM Albonico M Schulze KJ Savioli L Tielsch JM Serum ferritin erythrocyte pro-toporphyrin and hemoglobin are valid indicators of iron status of school children in a malaria-holoendemic population J Nutr 1997127293ndash8

38 Massaga JJ Kitua AY Lemnge MM Akida JA Malle LN Ronn AM Theander TG Bygbjerg IC Effect of intermittent treatment with amodiaquine on anaemia and malarial fevers in infants in Tanzania a randomised placebo-controlled trial Lancet 20033611853ndash60

39 Verhoef H West CE Kraaijenhagen R Nzyuko SM King R Mbandi MM van Laatum S Hogervorst R Schep C Kok FJ Malarial anemia leads to adequately increased erythropoiesis in asymptomatic Kenyan children Blood 20021003489ndash94

40 Stoltzfus RJ Chway HM Montresor A Tielsch JM Jape JK Albonico M Savioli L Low dose daily iron supplementation improves iron status and appetite but not anemia whereas quarterly anthelminthic treatment improves growth appetite and anemia in Zanzibari preschool children J Nutr 2004134348ndash56

41 Kurtzhals JA Addae MM Akanmori BD Dunyo S Koram KA Appawu MA Nkrumah FK Hviid L Anae-mia caused by asymptomatic Plasmodium falciparum infection in semi-immune African schoolchildren Trans R Soc Trop Med Hyg 199993623ndash7

42 Loyevsky M John C Dickens B Hu V Miller JH Gordeuk VR Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators Mol Biochem Parasitol 199910143ndash59

43 Scholl PF Tripathi AK Sullivan DJ Bioavailable iron and heme metabolism in Plasmodium falciparum Curr Top Microbiol Immunol 2005295293ndash324

44 Darbari D Loyevsky M Gordeuk V Kark JA Castro O Rana S Apprey V Kurantsin-Mills J Fluorescence meas-urements of the labile iron pool of sickle erythrocytes Blood 2003102357ndash64

45 Ginsburg H Iron acquisition by Plasmodium spp Para-sitol Today 199915466

46 Atamna H Ginsburg H Heme degradation in the presence of glutathione A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells J Biol Chem 199527024876ndash83

47 Gabay T Ginsburg H Hemoglobin denaturation and iron release in acidified red blood cell lysatemdasha possible source of iron for intraerythrocytic malaria parasites Exp Parasitol 199377261ndash72

48 Iyer JK Shi L Shankar AH Sullivan DJ Jr Zinc pro-toporphyrin IX binds heme crystals to inhibit the proc-ess of crystallization in Plasmodium falciparum Mol Med 20039175ndash82

49 Cabantchik ZI Moody-Haupt S Gordeuk VR Iron che-lators as anti-infectives malaria as a paradigm FEMS Immunol Med Microbiol 199926289ndash98

50 Hershko C Control of disease by selective iron deple-tion a novel therapeutic strategy utilizing iron chelators Baillieres Clin Haematol 19947965ndash1000

51 Pradines B Tall A Ramiandrasoa F Spiegel A Sokhna C Fusai T Mosnier J Daries W Trape JF Kunesch G Parzy D Rogier C In vitro activity of iron-binding compounds against Senegalese isolates of Plasmodium falciparum J Antimicrob Chemother 2006571093ndash9

52 Meshnick SR Yang YZ Lima V Kuypers F Kam-chonwongpaisan S Yuthavong Y Iron-dependent free radical generation from the antimalarial agent artem-isinin (qinghaosu) Antimicrob Agents Chemother 1993371108ndash14

53 Golenser J Domb A Mordechai-Daniel T Leshem B Luty A Kremsner P Iron chelators correlation between effects on Plasmodium spp and immune functions J Parasitol 200692170ndash7

54 Nyakeriga AM Williams TN Marsh K Wambua S Perlmann H Perlmann P Grandien A Troye-Blomberg M Cytokine mRNA expression and iron status in chil-dren living in a malaria endemic area Scand J Immunol 200561370ndash5

55 Smith HJ Meremikwu M Iron chelating agents for treating malaria Cochrane Database Syst Rev 2003CD001474

56 Weatherall DJ The global problem of genetic disease Ann Hum Biol 200532117ndash22

57 Williams TN Maitland K Bennett S Ganczakowski M Peto TE Newbold CI Bowden DK Weatherall DJ Clegg JB High incidence of malaria in alpha-thalassaemic children Nature 1996383522ndash5

58 Rees DC Williams TN Maitland K Clegg JB Weather-all DJ Alpha thalassaemia is associated with increased soluble transferrin receptor levels Br J Haematol 1998103365ndash9

59 Maitland K Williams TN Bennett S Newbold CI Peto TE Viji J Timothy R Clegg JB Weatherall DJ Bowden DK The interaction between Plasmodium falciparum and P vivax in children on Espiritu Santo island Van-uatu Trans R Soc Trop Med Hyg 199690614ndash20

60 Weatherall DJ Clegg JB Genetic variability in response to infection malaria and after Genes Immun 2002 3331ndash7

61 Parikh S Dorsey G Rosenthal PJ Host polymorphisms and the incidence of malaria in Ugandan children Am J Trop Med Hyg 200471750ndash3

62 Destro Bisol G Genetic resistance to malaria oxidative stress and hemoglobin oxidation Parassitologia 1999 41203ndash4

63 Cappadoro M Giribaldi G OrsquoBrien E Turrini F Mannu F Ulliers D Simula G Luzzatto L Arese P Early phago-cytosis of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes parasitized by Plasmodium falciparum may explain malaria protection in G6PD deficiency Blood 1998922527ndash34

64 Arese P Turrini F Schwarzer E Band 3complement-mediated recognition and removal of normally senes-cent and pathological human erythrocytes Cell Physiol Biochem 200516133ndash46

65 Atkinson SH Rockett K Sirugo G Bejon PA Fulford A OrsquoConnell M A Bailey R Kwiatkowski DP Prentice AM Seasonal Childhood Anaemia in West Africa Is Associated with the Haptoglobin 2-2 Genotype PLoS Med 20063e172

66 Cabrera G Cot M Migot-Nabias F Kremsner PG Deloron P Luty AJ The sickle cell trait is associated

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S539Iron metabolism and malaria

with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens J Infect Dis 20051911631ndash8

67 Williams TN Mwangi TW Roberts DJ Alexander ND Weatherall DJ Wambua S Kortok M Snow RW Marsh K An immune basis for malaria protection by the sickle cell trait PLoS Med 20052e128

68 Ayi K Turrini F Piga A Arese P Enhanced phagocyto-sis of ring-parasitized mutant erythrocytes a common mechanism that may explain protection against falci-parum malaria in sickle trait and beta-thalassemia trait Blood 20041043364ndash71

69 Roberts DJ Harris T Williams T The influence of inherited traits on malaria infection In Bellamy R ed Susceptibility to infectious diseases the importance of host genetics Cambridge Cambridge University Press 2004 139ndash84

70 Williams TN Mwangi TW Wambua S Alexander ND Kortok M Snow RW Marsh K Sickle cell trait and the risk of Plasmodium falciparum malaria and other child-hood diseases J Infect Dis 2005192178ndash86

71 Aidoo M Terlouw DJ Kolczak MS McElroy PD ter Kuile FO Kariuki S Nahlen BL Lal AA Udhayakumar V Protective effects of the sickle cell gene against malaria morbidity and mortality Lancet 20023591311ndash2

72 Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K Nega-tive epistasis between the malaria-protective effects of alpha+-thalassemia and the sickle cell trait Nat Genet 2005371253ndash7

73 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S Ascaso C Smith T MrsquoBoge B Greenwood BM The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS Trans R Soc Trop Med Hyg 199589289ndash92

74 Terlouw DJ Desai MR Wannemuehler KA Kariuki SK Pfeiffer CM Kager PA Shi YP Ter Kuile FO Relation between the response to iron supplementation and sickle cell hemoglobin phenotype in preschool children in western Kenya Am J Clin Nutr 200479466ndash72

75 Duffy PE Fried M Malaria in the pregnant woman Curr Top Microbiol Immunol 2005295169ndash200

76 Schellenberg D Menendez C Kahigwa E Aponte J Vidal J Tanner M Mshinda H Alonso P Intermittent treatment for malaria and anaemia control at time of routine vaccinations in Tanzanian infants a randomised placebo-controlled trial Lancet 20013571471ndash7

77 Schellenberg D Menendez C Aponte JJ Kahigwa E Tanner M Mshinda H Alonso P Intermittent preventive antimalarial treatment for Tanzanian infants follow-up to age 2 years of a randomised placebo-controlled trial Lancet 20053651481ndash3

78 OrsquoMeara WP Breman JG McKenzie FE The promise and potential challenges of intermittent preventive treat-ment for malaria in infants (IPTi) Malar J 2005433

79 White NJ Intermittent presumptive treatment for malaria PLoS Med 20052e3

80 Elagib AA Kider AO Akerstrom B Elbashir MI Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan Trans R Soc Trop Med Hyg 199892309ndash11

81 Minang JT Gyan BA Anchang JK Troye-Blomberg M Perlmann H Achidi EA Haptoglobin phenotypes and malaria infection in pregnant women at delivery in western Cameroon Acta Trop 200490107ndash14

82 Quaye IK Ekuban FA Goka BQ Adabayeri V Kurtzhals JA Gyan B Ankrah NA Hviid L Akanmori BD Hap-toglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria Trans R Soc Trop Med Hyg 200094216ndash9

83 Singh IP Walter H Bhasin MK Bhardwaj V Sudhakar K Genetic markers and malaria Observations in Gujarat India Hum Hered 19863631ndash6

84 Aucan C Walley AJ Greenwood BM Hill AV Hap-toglobin genotypes are not associated with resistance to severe malaria in The Gambia Trans R Soc Trop Med Hyg 200296327ndash8

85 Bienzle U Eggelte TA Adjei LA Dietz E Ehrhardt S Cramer JP Otchwemah RN Mockenhaupt FP Limited influence of haptoglobin genotypes on severe malaria in Ghanaian children Trop Med Int Health 200510668ndash71

86 Takeda M Kikuchi M Ubalee R Na-Bangchang K Ruangweerayut R Shibahara S Imai S Hirayama K Microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with susceptibility to cerebral malaria in Myanmar Jpn J Infect Dis 2005 58268ndash71

87 Shankar AH Nutritional modulation of malaria mor-bidity and mortality J Infect Dis 2000182 Suppl 1 S37ndash53

88 Gera T Sachdev HP Effect of iron supplementation on incidence of infectious illness in children systematic review Bmj 20023251142

Page 6: Iron metabolism and malaria

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S529Iron metabolism and malaria

partly explain the variations in response to iron supple-mentation reported by different studies other potential complicating factors that contribute to these variations are described in table 4

All but two studies [15 19] have found significant positive effects on markers of iron status in those receiving iron supplementation In the trial of van den Hombergh et al [19] the sample size was limited and baseline characteristics were significantly different between the supplementation and placebo groups Chippaux et al [15] found that anemic children who remained parasite free had increased hemoglobin levels postsupplementation but those that subsequently developed malaria did not The effect of supplementa-tion on hemoglobin concentrations ranged between 06 and 49 gdL with the highest increase occurring in a study that combined iron supplements with anti-malarial therapy [17] Other studies have also shown an additional advantage of iron plus antimalarials as regards hemoglobin recovery [16 18] However despite the hematological benefits all of these studies found nonsignificant increases in adverse malarial outcomes in the groups that received antimalarials plus iron including increased parasite density [16] risk of malaria [18] and treatment failure [17]

Six studies found no effect of iron supplements on malaria risk [19ndash24] of these three included large proportions of anemic subjects (74 to 94) [20 21 24] and one included only children with hemoglobin lt 5 gdL [19] Other studies that stratified by baseline hemoglobin levels [17 25] found that the greatest ben-efits occurred in the most anemic subgroups

Three studies found an increase in clinical malaria attacks in the iron-supplemented groups [10 11 25] and a further six studies found nonsignificant increases in malaria outcomes [14ndash18 26] One of the striking differences between study populations with significant increases in malaria outcomes and those with non-significant effects is access to health care and active treatment of malaria incident cases In fact all but one of the trials [21] that found no effect on malaria outcomes provided access to health care facilities or active follow-up and treatment of malaria incident cases This implies that the potential detrimental effects of iron supplementation may be curtailed by concurrent effective treatment of malaria infections However Verhoef et al and Nwanyanwu et al have shown potential treatment failure effects of combining sulfadoxinendashpyrimethamine with iron in the treatment of preexisting malaria suggesting that antimalarial therapy should precede supplementation [2 17 18]

These observations are further confirmed by a large study in Zanzibar by Sazawal et al [25] that showed increases in malaria-related morbidity and mortality in the iron-supplemented arms of a randomized control-led trial of ironfolate and ironfolate plus zinc versus placebo (summarized in table 2) A subgroup of this Sa

zaw

al[2

5]La

ncet

200

61ndash

35 m

o ir

on (1

25

mg)

+ fo

late

vs

iron

+ fo

late

+ zi

nc v

s pl

aceb

o m

orbi

d-ity

and

mor

talit

y ou

tcom

es a

sses

sed

N

= 3

215

5

43

wer

e pa

rasit

emic

at

bas

elin

eH

b gt

7 g

dL 5

7 o

f ch

ildre

n ha

d H

b lt

10 g

dL

at b

asel

ine

Trea

ted

subs

tudy

chil-

dren

with

clin

ical

m

alar

ia w

ith S

P at

ba

selin

e 6

mo

and

12

mo

Com

bine

d iro

n gr

oups

vs

pla-

cebo

Fo

r adv

erse

mal

aria

-rel

ated

ev

ents

RR

= 1

16

For c

ereb

ral m

alar

ia R

R =

122

Iron

+ fo

late

vs

plac

ebo

For c

ereb

ral m

alar

ia a

s a c

ause

of

dea

th R

R =

17

Subs

tudy

Lo

wer

rate

of a

dver

se e

vent

s in

child

ren

iron

defic

ient

at

base

line

Prot

ectiv

e ef

fect

of i

ron

+ fo

late

in

iron

-def

icie

nt a

nem

ic ch

il-dr

en R

R =

051

Sig

nific

ant d

iffer

ence

s as

repo

rted

by

the

auth

ors

RCT

ran

dom

ized

con

trol

led

tria

l H

b h

emog

lobi

n O

R o

dds

ratio

MC

V m

ean

corp

uscu

lar

volu

me

NS

not

sig

nific

ant

PCV

pac

ked

cell

volu

me

SP

sul

fado

xine

ndashpyr

imet

ham

ine

IPT

inte

rmitt

ent

prev

entiv

e th

erap

y IT

N i

nsec

ticid

e tr

eate

d be

dnet

s ]H

R h

azar

d ra

tio R

R re

lativ

e ris

k

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S530 A M Prentice et al

trial was investigated in more detail and consequently received more intensive diagnosis and treatment of malaria and other infections Substudy children with iron-deficiency anemia at baseline benefited sig-nificantly from iron supplementation in that they had reduced malaria and other infection-related hospital admissions and mortality [25]

The results of this recent study in Zanzibari children have raised new concerns about possible serious side effects of iron supplementation in populations where the etiology of anemia is not solely attributable to iron

deficiency and point to the need for a deeper under-standing of the complex biology of iron sequestration and redistribution between different storage and functional compartments and of the underlying host factors that influence these processes

Effect of malaria on iron metabolism

Erythropoietic iron requirement is met largely through recycling of senescent red blood cells through reticu-loendothelial macrophages where iron is repackaged onto transferrin for transport to the bone marrow [27] Red blood cells are predominantly engulfed directly by reticuloendothelial macrophages however up to 10 of normal recycling occurs as a result of intravascular hemolysis Hemoglobin is released and rapidly bound to haptoglobin and the resultant complex is cleared by liver parenchymal cells or the CD163 macrophagal receptor [28] Malaria-induced destruction of infected and noninfected red blood cells both stresses and impedes the capacity of reticuloendothelial macro-phages to recycle iron back to the bone marrow Intra-vascular rupture of parasitized red cells macrophagal phagocytosis of both parasitized and unparasitized red cells and hypersplenism all contribute to the patho-physiology of the anemia associated particularly with acute malaria

The local epidemiology and transmission character-istics of Plasmodium falciparum together with local drug treatment and intermittent preventive therapy

TABLE 3 Meta-analyses and reviews

First author Sourceyear Study design Findings

Shankar [87] J Infect Dis 2000 Meta-analysis of 13 RCTs of the effect of iron supplementation on malaria and iron status

RR for clinical malaria attack = 11 (NS)RR for slide positive for Plasmodium falci-

parum = 117Absolute increase in infection rate = 57 (NS)RR for spleen enlargement = 112 (NS)Mean increase in Hb = 125 gdLRR for anemia = 05

Oppenheimer [2] J Nutr 2001 Review of controlled interven-tion studies of iron supplemen-tation

Oral iron therapy increased clinical malaria in 5 out of 9 studies

No studies of iron therapy in malarious areas showed benefits on infectious morbidity

Does not report on effect on iron status

Gera [88] BMJ 2002 Systematic review of 28 RCTs of the effect of iron supplementa-tion or fortification in children on infectious illness (including 8 studies of the effect of iron supplementation on malaria)

Pooled OR for malaria-positive smear = 143 but OR when adjusted for baseline malaria smear = 124 (NS)

(The treatment effect increased by 289 times per unit increase in baseline malaria posi-tivity this supports the argument that iron supplementation of children with preexist-ing malaria increases their risk of remaining malaria positive)

Significant differences as reported by the authors RCT randomized controlled trial RR relative risk NS not significant Hb hemoglobin OR odds ratio

TABLE 4 Factors complicating assessment of the relationship between iron status and malaria and the response to iron sup-plementation in malaria-endemic populations

raquo Differences in dose duration and route of iron admin-istration

raquo Degree of malaria immunity in study individuals which can also be related to age and local malaria transmission patterns [7]

raquo Supplementation with iron and folate vs iron alone (especially as some antimalarials have antifolate action) [24]

raquo Markers of iron status used (the confounding effect of infection on serum markers of iron deficiency) [2 8]

raquo Baseline iron status iron-deficient individuals benefit [18 21]

raquo Access to health care and intensity of malaria surveil-lance and treatment during the trial [18 25]

raquo Hemoglobinopathies may affect anemia and response to iron supplementation as well as risk of malaria [9 73]

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S531Iron metabolism and malaria

(IPT) practices influence population immunity and resultant malarial clinical presentation as well as the epidemiology of anemia in a particular setting These factors may also influence the disturbance of iron metabolism and erythropoietic response to iron sup-plementation Acute malaria is associated predomi-nantly with a picture of fever hemolysis and oxidant stress whereas dyserythropoiesis predominates in the anemia of chronic malaria in a semiimmune patient [29] Acute malarial hemolysis represents a major stress on the homeostatic mechanisms of iron flux regulation that have evolved primarily to maintain erythroblast supply while minimizing the oxidant stress-associated effects of iron

Iron can be sequestered and trapped in reticuloen-dothelial macrophages as a result of both chronic and acute malaria and can present a picture of iron-deficient erythropoiesis associated with normal or increased bone marrow iron For instance bone marrow aspirates in 23 Thai patients with uncomplicated acute malaria (age 15 to 52 years) demonstrated malarial pigment in 22 of them Convalescent bone marrow aspirates in 16 patients (3 to 25 days after admission) demonstrated increased iron content compared with the admission sample [30] Five of six Gambian children (lt 5 years of age) with acute malaria had elevated stainable bone marrow iron and four of six children with chronic malaria and severe anemia (hemoglobin lt 6 gdL) had either normal or markedly increased levels of bone marrow stainable iron [31] Eighty-six percent of Indian children and adults (N = 26) with acute and 84 of those with chronic falciparum malaria and anemia (mean hemoglobin 54 gdL N = 38) had normal or increased bone marrow iron stores [32] Ferrokinetic studies involving the intravenous administration of 59Fe demonstrated low unsaturated iron-binding capacity and a rapid plasma iron disappearance time in both parasitemic and postparasitemic patients with acute and secondary (recent acute infection with persistent parasitemia) P falciparum and P vivax in Thai adults compared with controls [33] Incorporation of 59Fe into red blood cells was decreased in acute (N = 5) and secondary parasitemia (11 of 14) but found to be largely normal in the postparasitemic patients includ-ing 3 who were restudied from the parasitemic group Iron sequestration in acute malaria is cytokine driven (elevated tumor necrosis factor α [TNF-α] ILndash1 and interferon γ [IFN-γ] and diminished ILndash10) [29] prob-ably mediated via hepcidin however quantifying this phenomenon assessing how long it persists after acute malaria and in association with chronic malaria and assessing its importance in relation to malarial anemia malaria-associated immunosuppression and response to iron supplementation is difficult since there are few data Conventional indices of iron storage (eg ferritin) or of tissue supply (eg zinc protoporphyrin soluble transferrin receptor transferrin saturation) are

affected by inflammation [8 34ndash36] and the assess-ment of the iron status of young children in malarious areas with acute or chronic malaria is problematic [34] In a holoendemic environment ferritin and eryth-rocyte protoporphyrin were not affected by chronic malaria in older children [37] These indices also do not distinguish between iron deficiency and iron sequestration

Effect of malaria on response to iron supplementation

Malaria-induced anemia does not lead to loss of iron from the body However iron deficiency often coex-ists with malaria in areas of malaria transmission and therapy for severe postmalarial anemia commonly assumes a component due to preexisting iron defi-ciency Iron supplements are routinely prescribed both for severe malaria-associated anemia and for presumed iron-deficient anemia in a malaria-endemic environ-ment Few studies however have looked at the effect of acute malaria on the response to iron supplementation and even fewer have addressed the effect of chronic asymptomatic malaria More commonly studies either have either assessed the response to supplementation of children with anemia of undefined etiology in areas of coexistent malaria iron deficiency and hookworm or have randomized children who were anemic after malaria to a variety of hematinics In a study of 222 Malawian children (lt 5 years of age) with anemia after acute malaria the use of Fansidar and daily supplemen-tal iron resulted in a significantly greater hemoglobin recovery than Fansidar alone or Fansidar and weekly iron only in those children with initial hemoglobin between 5 and 8 gdL [17] However a larger propor-tion of the iron-treated children failed to clear their malaria In the Gambia 600 children (mean age 52 months mean hemoglobin 96 gdL) with uncompli-cated falciparum malaria randomized to receive chlo-roquine or Fansidar as treatment and then either iron folic acid or placebo for 28 days [22] demonstrated a significantly better hemoglobin response with iron than with placebo or folic acid (the difference in mean hemoglobin level after 1 month was 07 gdL) One hundred Tanzanian children (lt 30 months of age) with severe anemia (hemoglobin lt 5 gdL) were randomized either to receive daily iron supplementation or to be controls after antimalarial treatment [19] Among the 60 who completed the 12-week follow-up without a transfusion (30 in each group) there were no differ-ences in hemoglobin recovery From these studies the role of iron supplementation in the treatment of anemia after acute malaria is unclear and it is likely that the hemoglobin response to supplementation is influenced by both the direct inflammatory effect of malaria on iron absorption and utilization and preexistent iron

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S532 A M Prentice et al

deficiency which is impossible to assess in the presence of malaria In the Gambia we recently compared the absorption of stable-isotope-labeled iron in children anemic as a result of iron deficiency and children anemic after acute malaria Both groups were given 30 days of iron supplementation and the malaria group demonstrated significantly better hemoglobin recovery despite initially significantly reduced iron absorption (Doherty et al unpublished results) Utilization of sequestered iron is likely to be a major contributor to erythroblastic iron requirement after acute malaria

Studies of iron supplementation of populations of anemic children in malarious areas have reported either improved hemoglobin response or decreased prevalence of severe anemia [16 22 38 39] Incorpo-ration of antimalarial intervention arms is common Malaria transmission characteristics study design use of antecedent antimalarials differing iron supplemen-tation doses and differing outcome measures as well as different prevalence rates of iron deficiency and hook-worm infection have made the assessment of factors affecting hemoglobin response to iron supplementation difficult In particular the effect of chronic malaria on response to supplementation in high-transmission areas is unclear as the etiology of the anemia and the chronicity of malaria parasitemia are often undefined in study subjects In an area of intense transmission in Tanzania in which more than 80 of children (4 to 71 months old) were parasitemic at baseline and where malaria infection was strongly associated with hemo-globin supplementation improved the iron status and motor and language development of an iron-deficient population but not did not improve hemoglobin [21 36 40] The authors concluded that factors including malarial parasitemia or ineffective erythropoiesis due to inflammatory processes in a population with high levels of infectious morbidity and inflammation might have limited erythropoiesis

An inflammatory-mediated block to iron absorp-tion and utilization is likely to limit the erythropoietic response to supplemental iron after acute malaria how-ever it is unclear whether chronic parasitemia similarly limits the response to supplemental iron The asso-ciation of chronic malaria with anemia [39] stainable bone marrow iron [34] and increased cytokine levels [41] might suggest a probable effect and the eradica-tion of parasites has been associated with hemoglobin improvement without supplemental iron [31]

Iron metabolism by malaria parasites

In this section we consider whether the availability of iron in the host could modulate the efficiency with which malaria parasites can establish an infection and the severity of that infection What evidence is there to support the ldquonutritional immunityrdquo hypothesis that

host iron availability could limit parasite invasion or multiplication andor the clinical sequelae of para-site infection Support for the nutritional immunity hypothesis first stated in the 1970s has generally waned for the majority of pathogens [2] but there may still be a case for obligate intracellular pathogensmdashincluding Plasmodium spp

It may be informative to examine the research of other scientists than those typically involved in the cur-rent debate For example in order for this hypothesis to be truemdashat least in terms of the success of parasite invasion and replicationmdashit is a requirement that P falciparum be dependent on host iron sources for its survival Next is iron deficiency ever likely to be a limiting factor in the supply of iron to the parasite The most recent research suggests that P falciparum does utilize iron from the host but not from the abundant supplies available in erythrocyte hemoglobin the heme portion of which is quickly degraded to nontoxic but non-iron-bioavailable hemozoin or from the plasma via transferrin but from another source possibly an intraerythrocytic labile pool of ferrous iron [42 43] Interestingly measurements of this labile ferrous iron in normal and sickled erythrocytes indicate it to be positively associated with hemoglobin concentrations and negatively associated with plasma ferritin [44] However other researchers have reported evidence to suggest that the degradation of heme to hemozoin is incomplete and that 50 of heme may be degraded via an alternative pathway involving reduced glutathione and releasing bioavailable iron [45 46] As it has been estimated that less than 1 of heme iron would be sufficient to meet parasite iron requirements [47] iron deficiency would never induce iron-limited growth if hemoglobin were the iron source for parasites

Another mechanism by which iron deficiency may limit parasite growth is that proposed recently by Iyer et al [48] who demonstrated the inhibition of hemozoin formation from toxic free heme by the naturally occur-ring zinc protoporphyrin IX (ZPP) at levels likely to be encountered in anemic erythrocytes It is interesting to note that this is thought to be the mechanism by which the quinoline antimalarials act Furthermore Iyer et al demonstrated that quinolines competed for ZPP bind-ing and prevention of hemozoin formation It is pos-sible that via this mechanism moderate anemia could allow the persistence of low levels of parasitemia and therefore affect the development of exposure-related antibody repertoire and clinical immunitymdashwith consequent effects on future malarial incidence and malaria-associated anemia However the evidence for such an effect in human populations is currently limited due to the lack of longitudinal studies assessing ZPP levels and parasite prevalence and density from infancy onwards

Another research area that has been used to support the hypothesis of decreased iron availability is that

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S533Iron metabolism and malaria

of the effects of iron chelators on parasite growth in vitro and in vivo [49 50] Furthermore some antima-larial drugs such as the antibiotic cyclines including doxycycline are also iron chelators However iron chelators may not be acting by depriving the parasite of iron Alternative mechanisms have been suggested for some chelators including the induction of reactive oxygen species from dissociation of iron from heme and hemozoin as suggested for the lipophilic FR160 [51] similar to the suggested mechanism of artemisinin [52] Furthermore differences between the efficacy of chelators in vitro and in vivo have been associated with differences in immune modulation [53] This may suggest that iron status could affect malarial outcomes via direct effects on immune modulation as suggested by Nyakeriga et al [54] The evidence base for the effects of current iron-chelator therapies in reducing the prevalence density or clinical sequelae of malaria is weakmdashas outlined in a recent Cochrane review of clinical trials involving the use of either desferioxamine or the orally available deferiprone [55] in which all of the seven studies included had limitations relat-ing to study size relevance of study populations and more critically methodological and analytical faults However the authors of this review concluded that the results suggested possible benefits of treatment in cerebral malaria with a shorter recovery time from coma and decreased time to parasite clearance The initial justification for using iron-chelator therapy in cerebral malaria was based on the premise of prevent-ing iron-induced damage to brain cells resulting from hemolysis Therefore it is important to note that the possible benefits of iron-chelator therapy may not relate to limitation of iron for parasite growth and may there-fore not provide evidence in support of the nutritional immunity hypothesis

Iron malaria and hemoglobinopathies

How do hemoglobinopathies protect against parasite invasion or multiplication andor clinical sequelae of parasite infection Are these polymorphisms likely to affect the relationship between iron status or supple-mentation and malaria

J B S Haldane is credited with first postulat-ing heterozygote selection as an explanation for the high prevalence of the thalassemias and later other hemoglobinopathies He suggested that the small size reduced hemoglobin concentrations and increased resistance to hypertonic solutions of such cells may result in decreased parasite invasion or growth Although this hypothesis has been widely accepted for some time it has only recently been possible to dem-onstrate that these mutations have been maintained by selection mostly by malaria but possibly also other infectious causes However the extent and mechanisms

of protection are still debated At least in vitro many studies have failed to demonstrate decreased ability of parasites to invade or grow in thalassemic cells or cells containing hemoglobin S (HbS) Instead the mecha-nisms appear to be more complicated and possibly to vary between local conditions

The common polymorphisms involved in hemo-globin synthesis or red cell formation include sickle hemoglobin (HbS) HbC and HbE the α and β-thalassemias and South Asian ovalocytosis The geographic distribution of these varies across tropi-cal areas and can vary extensively even within closely related regions Current estimates of these polymor-phisms are often based on single sites and are likely to be underestimates [56] but a figure of 27 million carriers of the main hemoglobinopathies has been proposed [56] The carrier frequency for HbS is esti-mated at between 5 and 40 in populations across sub-Saharan Africa the Middle East and parts of South Asia HbC is limited to parts of West and North Africa whereas HbE is common in some parts of India and Southeast Asia with carrier rates up to 60 The thalassemias have the broadest geographic distribution and also the widest range of causative mutations and clinical outcomes The carrier frequencies for the more severe range of β-thalassemias is generally lower than for the α-thalassemias which are estimated to reach carrier frequencies of up to 20 in sub-Saharan Africa higher in Middle Eastern and Indian populations and up to 80 in some Pacific populations (reviewed in Williams et al [57] Rees et al [58] and Maitland et al [59])

In β-thalassemias excess α-globin chains precipitate in red cell precursors leading to ineffective erythropoi-esis and resulting in anemia in the context of increased iron absorption and iron accumulation The clinical expression of β-thalassemia varies widely depending on the exact genetic lesions inherited and interactions with other genetic loci including the α and γ globin genes β-Thalassemia trait and β-thalassemia interme-diate are often asymptomatic and may not be diagnosed except for mild anemia In α-thalassemia the excess β-chains form stable homotetramers which do not sig-nificantly affect erythropoiesis but cause an increased rate of hemolysis of mature cells The degree of the deficit of α-globin chains depends on the number of α-globin genes inactivated and unless three α-globin genes are lost the effects are subtle and various so that the condition will go largely undiagnosed It might be supposed that iron supplementation could be more deleterious in populations with a high prevalence of β-thalassemia mutations because of the inability to utilize the iron leading to increased iron availability to pathogens or iron-induced oxidant stress Interest-ingly Oppenheimer [2] reported that the increased susceptibility to malaria associated with parenteral iron in Papua New Guinean children was not apparent in

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S534 A M Prentice et al

single-deletion α-thalassemia compared with normal children

In a prospective casendashcontrol study in Papua New Guinea α-thalassemic α+ndash homozygotes and α+ndash heterozygotes had a greatly decreased risk of severe malaria (incidence rate ratio = 04 and 066) compared with controls [9] Furthermore protection was also observed for hospitalization from other infections possibly suggesting an immune component to the pro-tection [60] although the reduction of severe malaria may reduce infectious sequelae by invasive bacte-rial disease In apparent contrast α-thalassemia has also been associated with an increased prevalence of uncomplicated malaria in Vanuatu particularly in very young children with P vivax [57] It was suggested that increased red cell turnover in these children increased susceptibility to P vivax [58] resulting in cross-species immunity to P falciparum in later life [59] A similar finding was reported for glucose-6-phosphate dehy-drogenase (G6PD) deficiency in a cohort study in Uganda in which many other potential risk factors for malarial infection were controlled for (age water source use of prophylaxis bednet usage and proxim-ity to mosquito breeding sites) Female heterozygotes for G6PD had a significantly increased incidence of uncomplicated malaria (IRR = 13 p = 03) and a trend for increased parasite densities similar trends were seen for hemizygote males This was different from the pattern observed for HbS heterozygotes who had a nonsignificantly decreased incidence of uncomplicated malaria and decreased parasite densities [61]

A mechanism that has been suggested for G6PD defi-ciency and that may also be applicable to sickle (HbAS) and thalassemic cells involves decreased oxidative protection (G6PD) or increased constitutive oxidative stress of these cells (HbAS αβ thalassemias) especially when infected resulting in increased clearance of the cells from non-malaria-specific immune mechanisms essentially the same as the normal removal of old ldquosenescentrdquo red cells by phagocytes [62ndash64] It has been proposed that such a mechanism could prevent parasitemias from reaching critically high densities and therefore protect from severe malaria and also facilitate the development of antibody repertoires in children from the maintenance of low-grade infections in young children [65ndash67] In a slight modification of this hypothesis the increased phagocytic removal of early ring-stage infected cellsmdashcompared with schizonts and trophozoitesmdashhas been demonstrated for G6PD β-thalassemic and HbAS cells in vitro but not for α-thalassemic infected cells [68] The phagocytosis of ring compared with later stages may be advantageous since rings contain less hemozoin the buildup of which in monocytes has been associated with decreased func-tion Additionally the reduction of the later stages of parasite development may reduce the development of severe symptoms such as cerebral malaria from

reduced endothelial adhesion of late-stage infected red blood cells to receptors such as intracellular adhesion molecule-1 (ICAM-1)

The epidemiological evidence for a protective effect of HbAS suggests that the protective effects are great-est for severe disease (reviewed by Roberts et al [69]) In the most comprehensive study to date a detailed prospective cohort in two Kenyan populations it was reported that HbS heterozygotes had a significantly decreased risk of mild clinical malaria as assessed by active surveillance (50 decreased risk 95 confi-dence interval [CI] 26 to 67]) a 75 (95 CI 84 to 61) decreased risk of hospital admission for malaria and a 90 [95 CI 3 to 99] decreased risk of severe malaria (severe malarial anemia cerebral malaria or complicated malaria) [70] There was no effect of HbAS on the risk of asymptomatic infec-tions or of parasite density in asymptomatic infections assessed at four cross-sectional surveys There were significant decreases in parasite densities for all of the other categories of infection Additionally in this study unlike another in western Kenya [71] the protection was specific to malaria and did not extend to other common childhood infections including respiratory infections gastroenteritis and helminth infections

What influence the hemoglobinopathic and other polymorphisms may have on the effect of iron sup-plementation on malarial susceptibility is potentially dependent on the extent and mechanisms of protection from infection in the different genotypesmdashinfluences that are likely to be further complicated by differential effects according to age and malarial exposure and effects of coinheritance [72] The coinheritance of the HbS G6PD deficiency and α-thalassemia deletion alle-les is likely to be prevalent in sub-Saharan populations making the study of such effects in real populations extremely difficult by requiring very large sample sizes and complex statistical modeling

To the authorsrsquo knowledge only two published randomized controlled trials of iron supplementation have assessed the effects by genotypemdashin both cases by HbAS versus HbAA [73 74]

In the first trial involving Traditional Birth Attend-ant-administered routine iron supplementation to multigravid Gambian pregnant women Menendez et al [73] reported that although overall there were significant beneficial effects on hemoglobin and packed cell volume (PCV) and on birthweight these effects were entirely accounted for by women with the HbAA phenotype (N = 402 vs N = 98) whereas iron-supplemented HbAS women had lower HB PCV and birthweight than HbAA women receiving placebo Furthermore even in this relatively small study these interactions were statistically significant (p lt 01 for hematological indices at delivery baseline measurements as a covariate p lt 03 for birthweight maternal height included as a covariate) Overall

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S535Iron metabolism and malaria

there was no reported increase in susceptibility to malaria as assessed by the prevalence of peripheral malaria at late pregnancy and delivery or by placental histology Yet iron-supplemented HbAS women had an increased prevalence of placental malaria (76 [2229]) compared with iron-supplemented HbAA women (53 [83158]) placebo-treated HbAA women (59 [91154]) or placebo-treated HbAS women (58 [1933]) At the time of this study IPT prophylaxis was recommended only for primigravid pregnant women in the Gambia hence the choice of the study population What the effects of iron supplementation might be in either primigravidae or multigravidae receiving IPTmdashwhich is now recommended for all pregnant women in malaria-endemic countriesmdashhas not been assessed The protection afforded by the HbAS genotype is likely to vary according to gravidity and malarial endemic-ity In areas of high transmission the majority of the increased risk is borne by primigravidae whereas in areas of lower and highly defined seasonal transmis-sion the increased risk extends to a greater number of pregnancies [75] The protective effect of HbAS is thought to be greatest in relatively nonimmune young children who have not yet developed acquired immunity by exposure to a variety of clonal variants of P falciparum and therefore have not developed a full antibody repertoire to the variant surface antigens (VSA) expressed on the cell surfaces of parasitized red blood cells

In the second trial the effect of the HbAS phenotype on the response to iron supplementation in children was assessed in a subanalysis of a 2 times 2 randomized controlled trial of iron supplementation and inter-mittent preventive treatment (IPT) for malaria using sulfadoxinendashpyrimethamine in anemic Kenyan chil-dren (hemoglobin 7 to 109 gdL) [74] There was no reported increase in the susceptibility to clinical malaria or the prevalence of parasitemia at monthly screening associated with the iron supplementation alone or with IPT [16] whereas IPT plus iron was the most effective in increasing hemoglobin concentrations There were no significant statistical interactions between HbASAA phenotypes and treatment group However there was a nonsignificant increase in the incidence rate ratio of clinical malaria in the HbAS group not receiv-ing IPT during the 12 weeks of follow-up (IRR = 416 95 CI 05 to 346) and increased geometric mean parasite density in both groups but by far the biggest difference was seen in the group receiving IPT (6203 vs 1853 p = 08 for the interaction) The authors acknowledge that the number of clinical events was very small and that these findings would need veri-fication in a larger study since the number of HbAS individuals (approximately 25 to 30) in each treatment group versus approximately 100 HbAA individuals plus the short follow-up time means that the study was grossly underpowered to assess these outcomes If this

effect is real then the age group studied in this trial (2 to 36 months with 78 lt 18 months) should include the most affected although greater effects might be observed in areas of lower transmission and therefore also in a greater age range of children The results of these two trials warrant urgent further trials or retro-spective analysis of prior trials with sufficient power and detail to make firm conclusions on the effects of common polymorphisms on the response to iron sup-plementation which may be expected to vary by age group and transmission intensity

Clinical trials of IPT during infancy (IPTi) have demonstrated a reduction in the prevalence of anemia in young children in malaria-endemic areas [16 18 38 76] and in some trials a reduction in the incidence of clinical malaria [38 76] and morbidity and mortality in the first year of life [38 77] However the effects may vary depending on the timing of dosing choice of drug local levels of resistance and levels of transmission [78 79] On the basis of our analysis above the impact of IPTi plus iron supplementation may be modulated by levels of hemoglobinopathies and therefore suba-nalyses of these studies should be performed according to genotype wherever possible

Interactions of polymorphisms in host iron metabolism and regulatory proteins with malaria

Polymorphisms of haptoglobin a plasma protein that binds free hemoglobin released from lysed red blood cells recirculating the heme portion to the bone marrow through monocyte and macrophage uptake via CD136 have also been associated with malarial outcomes although reports are conflicting Hap-toglobin exists as three common phenotypes Hp1-1 1-2 and 2-2 In case-control studies in India Sudan Ghana and Cameroon the Hp2-2 phenotype has been associated with protection from severe malaria and placental infection [80ndash83] However two studies that have assessed associations with haptoglobin genotypes did not report any associations [84 85] In a cohort study in Gambian children the Hp2-2 genotype was associated with a greater drop in hemoglobin concen-trations across a malarial transmission season [65] The authors proposed that this effect may have been mediated through an increased prevalence of asymp-tomatic infection observed in the Hp2-2 group which contributed to anemia but could provide protection against severe malaria Interestingly similar but smaller drops in hemoglobin concentration were also observed for heterozygotes for G6PD and HbS We are currently analyzing the effects of low-dose iron supplementation during a malarial transmission season in a similar cohort of children

Inducible heme oxygenase (iHO-1) catalyzes the

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S536 A M Prentice et al

breakdown of heme to generate iron carbon monoxide and biliverdin and is expressed in monocytes and mac-rophages among other cells Biliverdin is subsequently degraded to bilirubin which has potent antioxidant effects Microsatellite polymorphisms in the number of tandem repeats in the promoter of iHO-1 have been variously associated with increased and decreased oxidant stress in various disease pathologies However in a case-control study of cerebral malaria patients in Myanmar homozygotes for the short number of repeats (lt 28) previously associated with higher levels of transcription of iHO-1 were significantly more likely to have cerebral malaria than uncomplicated malaria (odds ratio 314 p = 008) [86] It is not clear how this effect may be mediated but it is possible that it results from increased levels of free iron and resulting oxidant stress

In summary the mechanisms by which various genetic polymorphisms interact with malarial infec-tion are still not clear Furthermore it is not clear how they may affect a possible relationship between iron and malaria especially in relation to supplementation which should be differentiated from that of iron status The current evidence suggests that the heterozygous states of the hemoglobinopathies do not protect against malaria by a simple mechanism involving iron with-holding from the pathogen However the effects of iron supplementation in individuals with the most common polymorphisms should be carefully evaluated taking into account differences in transmission intensity and iron status at baseline

Conclusions

The evidence reviewed above tends to substantiate the concerns raised by the recent Pemba trial that universal administration of iron to children in malarious areas may be associated with adverse outcomes The mecha-nism by which this occurs is far from clear and merits

further research to test whether other chemical forms of supplementary iron might carry less risk There is also evidence that the risk profile will be altered by host genetic variations in hemoglobinopathies G6PD and genes regulating iron metabolism However these insights are not of great practical value because population screening and targeted supplementation programs are not feasible in the areas where iron defi-ciency is most prevalent Likewise the evidence that anemic children are probably at low risk for any adverse outcomes associated with iron supplementation implies a need for prescreening that may not be cost-effective or logistically feasible in developing-country settings

The evidence is fairly clear that malaria causes anemia by diverting iron away from bone marrow and erythropoiesis as part of the inflammatory response and hence iron administration alone is not likely to be the most effective means of combating the anemia Other therapeutic paradigms that combat the inflam-mation and adjust the timing of iron administra-tion to children recovering from malaria should be researched

We suggest that further research is still required to confirm the apparent relationships between iron status and malaria and that such studies should also focus on the underlying mechanisms of the putative interaction This might be achieved through the establishment of a multicountry collaboration to standardize protocols both for iron-supplementation interventions and for the assessment of iron and malaria status indicators Standardizing protocols across variations in age groups malaria transmission patterns and genetic distribu-tions of hemoglobinopathies will provide the evidence for a more targeted approach to policies of prevention and treatment of anemia in malaria-endemic regions

Until this evidence is gathered we recommend that iron supplementation in malarious areas must be accompanied by effective systems for ensuring univer-sal rapid access to diagnosis and treatment of malaria or by preventive therapy

References

1 WHO UNICEF Focusing on anaemia Towards an integrated approach for effective anaemia control Joint WHO UNICEF Statement Geneva Joint WHO UNICEF Statement 2004

2 Oppenheimer SJ Iron and its relation to immunity and infectious disease J Nutr 2001131616Sndash33S discussion 33Sndash35S

3 Murray MJ Murray AB Murray NJ Murray MB Diet and cerebral malaria the effect of famine and refeeding Am J Clin Nutr 19783157ndash61

4 Nyakeriga AM Troye-Blomberg M Dorfman JR Alexander ND Back R Kortok M Chemtai AK Marsh K Williams TN Iron deficiency and malaria among children living on the coast of Kenya J Infect Dis 2004 190439ndash47

5 Oppenheimer SJ Macfarlane SB Moody JB Bunari O Hendrickse RG Effect of iron prophylaxis on morbidity due to infectious disease report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 1986 80596ndash602

6 Shipton D Association between haemoglobin level and susceptibility to malaria a study of Gambian children [MSc dissertation] London London School of Hygiene and Tropical Medicine 2004

7 Snow RW Byass P Shenton FC Greenwood BM The relationship between anthropometric measurements and measurements of iron status and susceptibility to malaria in Gambian children Trans R Soc Trop Med Hyg 199185584ndash9

8 Asobayire FS Adou P Davidsson L Cook JD Hurrell

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S537Iron metabolism and malaria

RF Prevalence of iron deficiency with and without concurrent anemia in population groups with high prevalences of malaria and other infections a study in Cote drsquoIvoire Am J Clin Nutr 200174776ndash82

9 Allen SJ OrsquoDonnell A Alexander ND Alpers MP Peto TE Clegg JB Weatherall DJ alpha+-Thalassemia protects children against disease caused by other infec-tions as well as malaria Proc Natl Acad Sci U S A 1997 9414736ndash41

10 Murray MJ Murray AB Murray MB Murray CJ The adverse effect of iron repletion on the course of certain infections Br Med J 197821113ndash5

11 Smith AW Hendrickse RG Harrison C Hayes RJ Greenwood BM The effects on malaria of treatment of iron-deficiency anaemia with oral iron in Gambian children Ann Trop Paediatr 1989917ndash23

12 Oppenheimer SJ Gibson FD Macfarlane SB Moody JB Harrison C Spencer A Bunari O Iron supplementation increases prevalence and effects of malaria report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 198680603ndash12

13 Byles AB Drsquosa A Reduction of reaction due to iron dextran infusion using chloroquine Br Med J 19703625ndash7

14 Berger J Dyck JL Galan P Aplogan A Schneider D Traissac P Hercberg S Effect of daily iron supplementa-tion on iron status cell-mediated immunity and inci-dence of infections in 6ndash36 month old Togolese children Eur J Clin Nutr 20005429ndash35

15 Chippaux JP Schneider D Aplogan A Dyck JL Berger J [Effects of iron supplementation on malaria infection] Bull Soc Pathol Exot 19918454ndash62

16 Desai MR Mei JV Kariuki SK Wannemuehler KA Phil-lips-Howard PA Nahlen BL Kager PA Vulule JM ter Kuile FO Randomized controlled trial of daily iron sup-plementation and intermittent sulfadoxine-pyrimeth-amine for the treatment of mild childhood anemia in western Kenya J Infect Dis 2003187658ndash66

17 Nwanyanwu OC Ziba C Kazembe PN Gamadzi G Gandwe J Redd SC The effect of oral iron therapy during treatment for Plasmodium falciparum malaria with sulphadoxine-pyrimethamine on Malawian chil-dren under 5 years of age Ann Trop Med Parasitol 199690589ndash95

18 Verhoef H West CE Nzyuko SM de Vogel S van der Valk R Wanga MA Kuijsten A Veenemans J Kok FJ Intermittent administration of iron and sulfadoxine-py-rimethamine to control anaemia in Kenyan children a randomised controlled trial Lancet 2002360908ndash14

19 van den Hombergh J Dalderop E Smit Y Does iron therapy benefit children with severe malaria-associated anaemia A clinical trial with 12 weeks supplementation of oral iron in young children from the Turiani Division Tanzania J Trop Pediatr 199642220ndash7

20 Lawless JW Latham MC Stephenson LS Kinoti SN Pertet AM Iron supplementation improves appetite and growth in anemic Kenyan primary school children J Nutr 1994124645ndash54

21 Mebrahtu T Stoltzfus RJ Chwaya HM Jape JK Savioli L Montresor A Albonico M Tielsch JM Low-dose daily iron supplementation for 12 months does not increase the prevalence of malarial infection or den-sity of parasites in young Zanzibari children J Nutr 20041343037ndash41

22 Menendez C Kahigwa E Hirt R Vounatsou P Aponte JJ Font F Acosta CJ Schellenberg DM Galindo CM Kimario J Urassa H Brabin B Smith TA Kitua AY Tanner M Alonso PL Randomised placebo-controlled trial of iron supplementation and malaria chemoproph-ylaxis for prevention of severe anaemia and malaria in Tanzanian infants Lancet 1997350844ndash50

23 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S MrsquoBoge B Greenwood BM The effects of iron supplementation during pregnancy given by traditional birth attendants on the prevalence of anaemia and malaria Trans R Soc Trop Med Hyg 199488590ndash3

24 van Hensbroek MB Morris-Jones S Meisner S Jaffar S Bayo L Dackour R Phillips C Greenwood BM Iron but not folic acid combined with effective antimalarial therapy promotes haematological recovery in African children after acute falciparum malaria Trans R Soc Trop Med Hyg 199589672ndash6

25 Sazawal S Black RE Ramsan M Chwaya HM Stoltzfus RJ Dutta A Dhingra U Kabole I Deb S Othman MK Kabole FM Effects of routine prophylactic supplemen-tation with iron and folic acid on admission to hospital and mortality in preschool children in a high malaria transmission setting community-based randomised placebo-controlled trial Lancet 2006367133ndash43

26 Harvey PW Heywood PF Nesheim MC Galme K Zegans M Habicht JP Stephenson LS Radimer KL Brabin B Forsyth K et al The effect of iron therapy on malarial infection in Papua New Guinean schoolchil-dren Am J Trop Med Hyg 19894012ndash8

27 Andrews NC Iron homeostasis insights from genetics and animal models Nat Rev Genet 20001208ndash17

28 Kristiansen M Graversen JH Jacobsen C Sonne O Hoffman HJ Law SK Moestrup SK Identification of the haemoglobin scavenger receptor Nature 2001409 198ndash201

29 Wickramasinghe SN Abdalla SH Blood and bone marrow changes in malaria Baillieres Best Pract Res Clin Haematol 200013277ndash99

30 Phillips RE Looareesuwan S Warrell DA Lee SH Karbwang J Warrell MJ White NJ Swasdichai C Weatherall DJ The importance of anaemia in cerebral and uncomplicated falciparum malaria role of compli-cations dyserythropoiesis and iron sequestration Q J Med 198658305ndash23

31 Abdalla S Weatherall DJ Wickramasinghe SN Hughes M The anaemia of P falciparum malaria Br J Haematol 198046171ndash83

32 Sen R Bhatnagar BM Singh U Yadav MS Sehgal PK Patterns of erythropoiesis and anaemia in malaria J Commun Dis 199022247ndash53

33 Srichaikul T Wasanasomsithi M Poshyachinda V Panikbutr N Rabieb T Ferrokinetic studies and eryth-ropoiesis in malaria Arch Intern Med 1969124623ndash8

34 Das BS Thurnham DI Das DB Influence of malaria on markers of iron status in children implications for interpreting iron status in malaria-endemic communi-ties Br J Nutr 199778751ndash60

35 Menendez C Quinto LL Kahigwa E Alvarez L Fern-andez R Gimenez N Schellenberg D Aponte JJ Tanner M Alonso PL Effect of malaria on soluble transferrin receptor levels in Tanzanian infants Am J Trop Med Hyg 200165138ndash42

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S538 A M Prentice et al

36 Stoltzfus RJ Chwaya HM Montresor A Albonico M Savioli L Tielsch JM Malaria hookworms and recent fever are related to anemia and iron status indicators in 0- to 5-y old Zanzibari children and these relationships change with age J Nutr 20001301724ndash33

37 Stoltzfus RJ Chwaya HM Albonico M Schulze KJ Savioli L Tielsch JM Serum ferritin erythrocyte pro-toporphyrin and hemoglobin are valid indicators of iron status of school children in a malaria-holoendemic population J Nutr 1997127293ndash8

38 Massaga JJ Kitua AY Lemnge MM Akida JA Malle LN Ronn AM Theander TG Bygbjerg IC Effect of intermittent treatment with amodiaquine on anaemia and malarial fevers in infants in Tanzania a randomised placebo-controlled trial Lancet 20033611853ndash60

39 Verhoef H West CE Kraaijenhagen R Nzyuko SM King R Mbandi MM van Laatum S Hogervorst R Schep C Kok FJ Malarial anemia leads to adequately increased erythropoiesis in asymptomatic Kenyan children Blood 20021003489ndash94

40 Stoltzfus RJ Chway HM Montresor A Tielsch JM Jape JK Albonico M Savioli L Low dose daily iron supplementation improves iron status and appetite but not anemia whereas quarterly anthelminthic treatment improves growth appetite and anemia in Zanzibari preschool children J Nutr 2004134348ndash56

41 Kurtzhals JA Addae MM Akanmori BD Dunyo S Koram KA Appawu MA Nkrumah FK Hviid L Anae-mia caused by asymptomatic Plasmodium falciparum infection in semi-immune African schoolchildren Trans R Soc Trop Med Hyg 199993623ndash7

42 Loyevsky M John C Dickens B Hu V Miller JH Gordeuk VR Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators Mol Biochem Parasitol 199910143ndash59

43 Scholl PF Tripathi AK Sullivan DJ Bioavailable iron and heme metabolism in Plasmodium falciparum Curr Top Microbiol Immunol 2005295293ndash324

44 Darbari D Loyevsky M Gordeuk V Kark JA Castro O Rana S Apprey V Kurantsin-Mills J Fluorescence meas-urements of the labile iron pool of sickle erythrocytes Blood 2003102357ndash64

45 Ginsburg H Iron acquisition by Plasmodium spp Para-sitol Today 199915466

46 Atamna H Ginsburg H Heme degradation in the presence of glutathione A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells J Biol Chem 199527024876ndash83

47 Gabay T Ginsburg H Hemoglobin denaturation and iron release in acidified red blood cell lysatemdasha possible source of iron for intraerythrocytic malaria parasites Exp Parasitol 199377261ndash72

48 Iyer JK Shi L Shankar AH Sullivan DJ Jr Zinc pro-toporphyrin IX binds heme crystals to inhibit the proc-ess of crystallization in Plasmodium falciparum Mol Med 20039175ndash82

49 Cabantchik ZI Moody-Haupt S Gordeuk VR Iron che-lators as anti-infectives malaria as a paradigm FEMS Immunol Med Microbiol 199926289ndash98

50 Hershko C Control of disease by selective iron deple-tion a novel therapeutic strategy utilizing iron chelators Baillieres Clin Haematol 19947965ndash1000

51 Pradines B Tall A Ramiandrasoa F Spiegel A Sokhna C Fusai T Mosnier J Daries W Trape JF Kunesch G Parzy D Rogier C In vitro activity of iron-binding compounds against Senegalese isolates of Plasmodium falciparum J Antimicrob Chemother 2006571093ndash9

52 Meshnick SR Yang YZ Lima V Kuypers F Kam-chonwongpaisan S Yuthavong Y Iron-dependent free radical generation from the antimalarial agent artem-isinin (qinghaosu) Antimicrob Agents Chemother 1993371108ndash14

53 Golenser J Domb A Mordechai-Daniel T Leshem B Luty A Kremsner P Iron chelators correlation between effects on Plasmodium spp and immune functions J Parasitol 200692170ndash7

54 Nyakeriga AM Williams TN Marsh K Wambua S Perlmann H Perlmann P Grandien A Troye-Blomberg M Cytokine mRNA expression and iron status in chil-dren living in a malaria endemic area Scand J Immunol 200561370ndash5

55 Smith HJ Meremikwu M Iron chelating agents for treating malaria Cochrane Database Syst Rev 2003CD001474

56 Weatherall DJ The global problem of genetic disease Ann Hum Biol 200532117ndash22

57 Williams TN Maitland K Bennett S Ganczakowski M Peto TE Newbold CI Bowden DK Weatherall DJ Clegg JB High incidence of malaria in alpha-thalassaemic children Nature 1996383522ndash5

58 Rees DC Williams TN Maitland K Clegg JB Weather-all DJ Alpha thalassaemia is associated with increased soluble transferrin receptor levels Br J Haematol 1998103365ndash9

59 Maitland K Williams TN Bennett S Newbold CI Peto TE Viji J Timothy R Clegg JB Weatherall DJ Bowden DK The interaction between Plasmodium falciparum and P vivax in children on Espiritu Santo island Van-uatu Trans R Soc Trop Med Hyg 199690614ndash20

60 Weatherall DJ Clegg JB Genetic variability in response to infection malaria and after Genes Immun 2002 3331ndash7

61 Parikh S Dorsey G Rosenthal PJ Host polymorphisms and the incidence of malaria in Ugandan children Am J Trop Med Hyg 200471750ndash3

62 Destro Bisol G Genetic resistance to malaria oxidative stress and hemoglobin oxidation Parassitologia 1999 41203ndash4

63 Cappadoro M Giribaldi G OrsquoBrien E Turrini F Mannu F Ulliers D Simula G Luzzatto L Arese P Early phago-cytosis of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes parasitized by Plasmodium falciparum may explain malaria protection in G6PD deficiency Blood 1998922527ndash34

64 Arese P Turrini F Schwarzer E Band 3complement-mediated recognition and removal of normally senes-cent and pathological human erythrocytes Cell Physiol Biochem 200516133ndash46

65 Atkinson SH Rockett K Sirugo G Bejon PA Fulford A OrsquoConnell M A Bailey R Kwiatkowski DP Prentice AM Seasonal Childhood Anaemia in West Africa Is Associated with the Haptoglobin 2-2 Genotype PLoS Med 20063e172

66 Cabrera G Cot M Migot-Nabias F Kremsner PG Deloron P Luty AJ The sickle cell trait is associated

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S539Iron metabolism and malaria

with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens J Infect Dis 20051911631ndash8

67 Williams TN Mwangi TW Roberts DJ Alexander ND Weatherall DJ Wambua S Kortok M Snow RW Marsh K An immune basis for malaria protection by the sickle cell trait PLoS Med 20052e128

68 Ayi K Turrini F Piga A Arese P Enhanced phagocyto-sis of ring-parasitized mutant erythrocytes a common mechanism that may explain protection against falci-parum malaria in sickle trait and beta-thalassemia trait Blood 20041043364ndash71

69 Roberts DJ Harris T Williams T The influence of inherited traits on malaria infection In Bellamy R ed Susceptibility to infectious diseases the importance of host genetics Cambridge Cambridge University Press 2004 139ndash84

70 Williams TN Mwangi TW Wambua S Alexander ND Kortok M Snow RW Marsh K Sickle cell trait and the risk of Plasmodium falciparum malaria and other child-hood diseases J Infect Dis 2005192178ndash86

71 Aidoo M Terlouw DJ Kolczak MS McElroy PD ter Kuile FO Kariuki S Nahlen BL Lal AA Udhayakumar V Protective effects of the sickle cell gene against malaria morbidity and mortality Lancet 20023591311ndash2

72 Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K Nega-tive epistasis between the malaria-protective effects of alpha+-thalassemia and the sickle cell trait Nat Genet 2005371253ndash7

73 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S Ascaso C Smith T MrsquoBoge B Greenwood BM The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS Trans R Soc Trop Med Hyg 199589289ndash92

74 Terlouw DJ Desai MR Wannemuehler KA Kariuki SK Pfeiffer CM Kager PA Shi YP Ter Kuile FO Relation between the response to iron supplementation and sickle cell hemoglobin phenotype in preschool children in western Kenya Am J Clin Nutr 200479466ndash72

75 Duffy PE Fried M Malaria in the pregnant woman Curr Top Microbiol Immunol 2005295169ndash200

76 Schellenberg D Menendez C Kahigwa E Aponte J Vidal J Tanner M Mshinda H Alonso P Intermittent treatment for malaria and anaemia control at time of routine vaccinations in Tanzanian infants a randomised placebo-controlled trial Lancet 20013571471ndash7

77 Schellenberg D Menendez C Aponte JJ Kahigwa E Tanner M Mshinda H Alonso P Intermittent preventive antimalarial treatment for Tanzanian infants follow-up to age 2 years of a randomised placebo-controlled trial Lancet 20053651481ndash3

78 OrsquoMeara WP Breman JG McKenzie FE The promise and potential challenges of intermittent preventive treat-ment for malaria in infants (IPTi) Malar J 2005433

79 White NJ Intermittent presumptive treatment for malaria PLoS Med 20052e3

80 Elagib AA Kider AO Akerstrom B Elbashir MI Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan Trans R Soc Trop Med Hyg 199892309ndash11

81 Minang JT Gyan BA Anchang JK Troye-Blomberg M Perlmann H Achidi EA Haptoglobin phenotypes and malaria infection in pregnant women at delivery in western Cameroon Acta Trop 200490107ndash14

82 Quaye IK Ekuban FA Goka BQ Adabayeri V Kurtzhals JA Gyan B Ankrah NA Hviid L Akanmori BD Hap-toglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria Trans R Soc Trop Med Hyg 200094216ndash9

83 Singh IP Walter H Bhasin MK Bhardwaj V Sudhakar K Genetic markers and malaria Observations in Gujarat India Hum Hered 19863631ndash6

84 Aucan C Walley AJ Greenwood BM Hill AV Hap-toglobin genotypes are not associated with resistance to severe malaria in The Gambia Trans R Soc Trop Med Hyg 200296327ndash8

85 Bienzle U Eggelte TA Adjei LA Dietz E Ehrhardt S Cramer JP Otchwemah RN Mockenhaupt FP Limited influence of haptoglobin genotypes on severe malaria in Ghanaian children Trop Med Int Health 200510668ndash71

86 Takeda M Kikuchi M Ubalee R Na-Bangchang K Ruangweerayut R Shibahara S Imai S Hirayama K Microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with susceptibility to cerebral malaria in Myanmar Jpn J Infect Dis 2005 58268ndash71

87 Shankar AH Nutritional modulation of malaria mor-bidity and mortality J Infect Dis 2000182 Suppl 1 S37ndash53

88 Gera T Sachdev HP Effect of iron supplementation on incidence of infectious illness in children systematic review Bmj 20023251142

Page 7: Iron metabolism and malaria

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S530 A M Prentice et al

trial was investigated in more detail and consequently received more intensive diagnosis and treatment of malaria and other infections Substudy children with iron-deficiency anemia at baseline benefited sig-nificantly from iron supplementation in that they had reduced malaria and other infection-related hospital admissions and mortality [25]

The results of this recent study in Zanzibari children have raised new concerns about possible serious side effects of iron supplementation in populations where the etiology of anemia is not solely attributable to iron

deficiency and point to the need for a deeper under-standing of the complex biology of iron sequestration and redistribution between different storage and functional compartments and of the underlying host factors that influence these processes

Effect of malaria on iron metabolism

Erythropoietic iron requirement is met largely through recycling of senescent red blood cells through reticu-loendothelial macrophages where iron is repackaged onto transferrin for transport to the bone marrow [27] Red blood cells are predominantly engulfed directly by reticuloendothelial macrophages however up to 10 of normal recycling occurs as a result of intravascular hemolysis Hemoglobin is released and rapidly bound to haptoglobin and the resultant complex is cleared by liver parenchymal cells or the CD163 macrophagal receptor [28] Malaria-induced destruction of infected and noninfected red blood cells both stresses and impedes the capacity of reticuloendothelial macro-phages to recycle iron back to the bone marrow Intra-vascular rupture of parasitized red cells macrophagal phagocytosis of both parasitized and unparasitized red cells and hypersplenism all contribute to the patho-physiology of the anemia associated particularly with acute malaria

The local epidemiology and transmission character-istics of Plasmodium falciparum together with local drug treatment and intermittent preventive therapy

TABLE 3 Meta-analyses and reviews

First author Sourceyear Study design Findings

Shankar [87] J Infect Dis 2000 Meta-analysis of 13 RCTs of the effect of iron supplementation on malaria and iron status

RR for clinical malaria attack = 11 (NS)RR for slide positive for Plasmodium falci-

parum = 117Absolute increase in infection rate = 57 (NS)RR for spleen enlargement = 112 (NS)Mean increase in Hb = 125 gdLRR for anemia = 05

Oppenheimer [2] J Nutr 2001 Review of controlled interven-tion studies of iron supplemen-tation

Oral iron therapy increased clinical malaria in 5 out of 9 studies

No studies of iron therapy in malarious areas showed benefits on infectious morbidity

Does not report on effect on iron status

Gera [88] BMJ 2002 Systematic review of 28 RCTs of the effect of iron supplementa-tion or fortification in children on infectious illness (including 8 studies of the effect of iron supplementation on malaria)

Pooled OR for malaria-positive smear = 143 but OR when adjusted for baseline malaria smear = 124 (NS)

(The treatment effect increased by 289 times per unit increase in baseline malaria posi-tivity this supports the argument that iron supplementation of children with preexist-ing malaria increases their risk of remaining malaria positive)

Significant differences as reported by the authors RCT randomized controlled trial RR relative risk NS not significant Hb hemoglobin OR odds ratio

TABLE 4 Factors complicating assessment of the relationship between iron status and malaria and the response to iron sup-plementation in malaria-endemic populations

raquo Differences in dose duration and route of iron admin-istration

raquo Degree of malaria immunity in study individuals which can also be related to age and local malaria transmission patterns [7]

raquo Supplementation with iron and folate vs iron alone (especially as some antimalarials have antifolate action) [24]

raquo Markers of iron status used (the confounding effect of infection on serum markers of iron deficiency) [2 8]

raquo Baseline iron status iron-deficient individuals benefit [18 21]

raquo Access to health care and intensity of malaria surveil-lance and treatment during the trial [18 25]

raquo Hemoglobinopathies may affect anemia and response to iron supplementation as well as risk of malaria [9 73]

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S531Iron metabolism and malaria

(IPT) practices influence population immunity and resultant malarial clinical presentation as well as the epidemiology of anemia in a particular setting These factors may also influence the disturbance of iron metabolism and erythropoietic response to iron sup-plementation Acute malaria is associated predomi-nantly with a picture of fever hemolysis and oxidant stress whereas dyserythropoiesis predominates in the anemia of chronic malaria in a semiimmune patient [29] Acute malarial hemolysis represents a major stress on the homeostatic mechanisms of iron flux regulation that have evolved primarily to maintain erythroblast supply while minimizing the oxidant stress-associated effects of iron

Iron can be sequestered and trapped in reticuloen-dothelial macrophages as a result of both chronic and acute malaria and can present a picture of iron-deficient erythropoiesis associated with normal or increased bone marrow iron For instance bone marrow aspirates in 23 Thai patients with uncomplicated acute malaria (age 15 to 52 years) demonstrated malarial pigment in 22 of them Convalescent bone marrow aspirates in 16 patients (3 to 25 days after admission) demonstrated increased iron content compared with the admission sample [30] Five of six Gambian children (lt 5 years of age) with acute malaria had elevated stainable bone marrow iron and four of six children with chronic malaria and severe anemia (hemoglobin lt 6 gdL) had either normal or markedly increased levels of bone marrow stainable iron [31] Eighty-six percent of Indian children and adults (N = 26) with acute and 84 of those with chronic falciparum malaria and anemia (mean hemoglobin 54 gdL N = 38) had normal or increased bone marrow iron stores [32] Ferrokinetic studies involving the intravenous administration of 59Fe demonstrated low unsaturated iron-binding capacity and a rapid plasma iron disappearance time in both parasitemic and postparasitemic patients with acute and secondary (recent acute infection with persistent parasitemia) P falciparum and P vivax in Thai adults compared with controls [33] Incorporation of 59Fe into red blood cells was decreased in acute (N = 5) and secondary parasitemia (11 of 14) but found to be largely normal in the postparasitemic patients includ-ing 3 who were restudied from the parasitemic group Iron sequestration in acute malaria is cytokine driven (elevated tumor necrosis factor α [TNF-α] ILndash1 and interferon γ [IFN-γ] and diminished ILndash10) [29] prob-ably mediated via hepcidin however quantifying this phenomenon assessing how long it persists after acute malaria and in association with chronic malaria and assessing its importance in relation to malarial anemia malaria-associated immunosuppression and response to iron supplementation is difficult since there are few data Conventional indices of iron storage (eg ferritin) or of tissue supply (eg zinc protoporphyrin soluble transferrin receptor transferrin saturation) are

affected by inflammation [8 34ndash36] and the assess-ment of the iron status of young children in malarious areas with acute or chronic malaria is problematic [34] In a holoendemic environment ferritin and eryth-rocyte protoporphyrin were not affected by chronic malaria in older children [37] These indices also do not distinguish between iron deficiency and iron sequestration

Effect of malaria on response to iron supplementation

Malaria-induced anemia does not lead to loss of iron from the body However iron deficiency often coex-ists with malaria in areas of malaria transmission and therapy for severe postmalarial anemia commonly assumes a component due to preexisting iron defi-ciency Iron supplements are routinely prescribed both for severe malaria-associated anemia and for presumed iron-deficient anemia in a malaria-endemic environ-ment Few studies however have looked at the effect of acute malaria on the response to iron supplementation and even fewer have addressed the effect of chronic asymptomatic malaria More commonly studies either have either assessed the response to supplementation of children with anemia of undefined etiology in areas of coexistent malaria iron deficiency and hookworm or have randomized children who were anemic after malaria to a variety of hematinics In a study of 222 Malawian children (lt 5 years of age) with anemia after acute malaria the use of Fansidar and daily supplemen-tal iron resulted in a significantly greater hemoglobin recovery than Fansidar alone or Fansidar and weekly iron only in those children with initial hemoglobin between 5 and 8 gdL [17] However a larger propor-tion of the iron-treated children failed to clear their malaria In the Gambia 600 children (mean age 52 months mean hemoglobin 96 gdL) with uncompli-cated falciparum malaria randomized to receive chlo-roquine or Fansidar as treatment and then either iron folic acid or placebo for 28 days [22] demonstrated a significantly better hemoglobin response with iron than with placebo or folic acid (the difference in mean hemoglobin level after 1 month was 07 gdL) One hundred Tanzanian children (lt 30 months of age) with severe anemia (hemoglobin lt 5 gdL) were randomized either to receive daily iron supplementation or to be controls after antimalarial treatment [19] Among the 60 who completed the 12-week follow-up without a transfusion (30 in each group) there were no differ-ences in hemoglobin recovery From these studies the role of iron supplementation in the treatment of anemia after acute malaria is unclear and it is likely that the hemoglobin response to supplementation is influenced by both the direct inflammatory effect of malaria on iron absorption and utilization and preexistent iron

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S532 A M Prentice et al

deficiency which is impossible to assess in the presence of malaria In the Gambia we recently compared the absorption of stable-isotope-labeled iron in children anemic as a result of iron deficiency and children anemic after acute malaria Both groups were given 30 days of iron supplementation and the malaria group demonstrated significantly better hemoglobin recovery despite initially significantly reduced iron absorption (Doherty et al unpublished results) Utilization of sequestered iron is likely to be a major contributor to erythroblastic iron requirement after acute malaria

Studies of iron supplementation of populations of anemic children in malarious areas have reported either improved hemoglobin response or decreased prevalence of severe anemia [16 22 38 39] Incorpo-ration of antimalarial intervention arms is common Malaria transmission characteristics study design use of antecedent antimalarials differing iron supplemen-tation doses and differing outcome measures as well as different prevalence rates of iron deficiency and hook-worm infection have made the assessment of factors affecting hemoglobin response to iron supplementation difficult In particular the effect of chronic malaria on response to supplementation in high-transmission areas is unclear as the etiology of the anemia and the chronicity of malaria parasitemia are often undefined in study subjects In an area of intense transmission in Tanzania in which more than 80 of children (4 to 71 months old) were parasitemic at baseline and where malaria infection was strongly associated with hemo-globin supplementation improved the iron status and motor and language development of an iron-deficient population but not did not improve hemoglobin [21 36 40] The authors concluded that factors including malarial parasitemia or ineffective erythropoiesis due to inflammatory processes in a population with high levels of infectious morbidity and inflammation might have limited erythropoiesis

An inflammatory-mediated block to iron absorp-tion and utilization is likely to limit the erythropoietic response to supplemental iron after acute malaria how-ever it is unclear whether chronic parasitemia similarly limits the response to supplemental iron The asso-ciation of chronic malaria with anemia [39] stainable bone marrow iron [34] and increased cytokine levels [41] might suggest a probable effect and the eradica-tion of parasites has been associated with hemoglobin improvement without supplemental iron [31]

Iron metabolism by malaria parasites

In this section we consider whether the availability of iron in the host could modulate the efficiency with which malaria parasites can establish an infection and the severity of that infection What evidence is there to support the ldquonutritional immunityrdquo hypothesis that

host iron availability could limit parasite invasion or multiplication andor the clinical sequelae of para-site infection Support for the nutritional immunity hypothesis first stated in the 1970s has generally waned for the majority of pathogens [2] but there may still be a case for obligate intracellular pathogensmdashincluding Plasmodium spp

It may be informative to examine the research of other scientists than those typically involved in the cur-rent debate For example in order for this hypothesis to be truemdashat least in terms of the success of parasite invasion and replicationmdashit is a requirement that P falciparum be dependent on host iron sources for its survival Next is iron deficiency ever likely to be a limiting factor in the supply of iron to the parasite The most recent research suggests that P falciparum does utilize iron from the host but not from the abundant supplies available in erythrocyte hemoglobin the heme portion of which is quickly degraded to nontoxic but non-iron-bioavailable hemozoin or from the plasma via transferrin but from another source possibly an intraerythrocytic labile pool of ferrous iron [42 43] Interestingly measurements of this labile ferrous iron in normal and sickled erythrocytes indicate it to be positively associated with hemoglobin concentrations and negatively associated with plasma ferritin [44] However other researchers have reported evidence to suggest that the degradation of heme to hemozoin is incomplete and that 50 of heme may be degraded via an alternative pathway involving reduced glutathione and releasing bioavailable iron [45 46] As it has been estimated that less than 1 of heme iron would be sufficient to meet parasite iron requirements [47] iron deficiency would never induce iron-limited growth if hemoglobin were the iron source for parasites

Another mechanism by which iron deficiency may limit parasite growth is that proposed recently by Iyer et al [48] who demonstrated the inhibition of hemozoin formation from toxic free heme by the naturally occur-ring zinc protoporphyrin IX (ZPP) at levels likely to be encountered in anemic erythrocytes It is interesting to note that this is thought to be the mechanism by which the quinoline antimalarials act Furthermore Iyer et al demonstrated that quinolines competed for ZPP bind-ing and prevention of hemozoin formation It is pos-sible that via this mechanism moderate anemia could allow the persistence of low levels of parasitemia and therefore affect the development of exposure-related antibody repertoire and clinical immunitymdashwith consequent effects on future malarial incidence and malaria-associated anemia However the evidence for such an effect in human populations is currently limited due to the lack of longitudinal studies assessing ZPP levels and parasite prevalence and density from infancy onwards

Another research area that has been used to support the hypothesis of decreased iron availability is that

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S533Iron metabolism and malaria

of the effects of iron chelators on parasite growth in vitro and in vivo [49 50] Furthermore some antima-larial drugs such as the antibiotic cyclines including doxycycline are also iron chelators However iron chelators may not be acting by depriving the parasite of iron Alternative mechanisms have been suggested for some chelators including the induction of reactive oxygen species from dissociation of iron from heme and hemozoin as suggested for the lipophilic FR160 [51] similar to the suggested mechanism of artemisinin [52] Furthermore differences between the efficacy of chelators in vitro and in vivo have been associated with differences in immune modulation [53] This may suggest that iron status could affect malarial outcomes via direct effects on immune modulation as suggested by Nyakeriga et al [54] The evidence base for the effects of current iron-chelator therapies in reducing the prevalence density or clinical sequelae of malaria is weakmdashas outlined in a recent Cochrane review of clinical trials involving the use of either desferioxamine or the orally available deferiprone [55] in which all of the seven studies included had limitations relat-ing to study size relevance of study populations and more critically methodological and analytical faults However the authors of this review concluded that the results suggested possible benefits of treatment in cerebral malaria with a shorter recovery time from coma and decreased time to parasite clearance The initial justification for using iron-chelator therapy in cerebral malaria was based on the premise of prevent-ing iron-induced damage to brain cells resulting from hemolysis Therefore it is important to note that the possible benefits of iron-chelator therapy may not relate to limitation of iron for parasite growth and may there-fore not provide evidence in support of the nutritional immunity hypothesis

Iron malaria and hemoglobinopathies

How do hemoglobinopathies protect against parasite invasion or multiplication andor clinical sequelae of parasite infection Are these polymorphisms likely to affect the relationship between iron status or supple-mentation and malaria

J B S Haldane is credited with first postulat-ing heterozygote selection as an explanation for the high prevalence of the thalassemias and later other hemoglobinopathies He suggested that the small size reduced hemoglobin concentrations and increased resistance to hypertonic solutions of such cells may result in decreased parasite invasion or growth Although this hypothesis has been widely accepted for some time it has only recently been possible to dem-onstrate that these mutations have been maintained by selection mostly by malaria but possibly also other infectious causes However the extent and mechanisms

of protection are still debated At least in vitro many studies have failed to demonstrate decreased ability of parasites to invade or grow in thalassemic cells or cells containing hemoglobin S (HbS) Instead the mecha-nisms appear to be more complicated and possibly to vary between local conditions

The common polymorphisms involved in hemo-globin synthesis or red cell formation include sickle hemoglobin (HbS) HbC and HbE the α and β-thalassemias and South Asian ovalocytosis The geographic distribution of these varies across tropi-cal areas and can vary extensively even within closely related regions Current estimates of these polymor-phisms are often based on single sites and are likely to be underestimates [56] but a figure of 27 million carriers of the main hemoglobinopathies has been proposed [56] The carrier frequency for HbS is esti-mated at between 5 and 40 in populations across sub-Saharan Africa the Middle East and parts of South Asia HbC is limited to parts of West and North Africa whereas HbE is common in some parts of India and Southeast Asia with carrier rates up to 60 The thalassemias have the broadest geographic distribution and also the widest range of causative mutations and clinical outcomes The carrier frequencies for the more severe range of β-thalassemias is generally lower than for the α-thalassemias which are estimated to reach carrier frequencies of up to 20 in sub-Saharan Africa higher in Middle Eastern and Indian populations and up to 80 in some Pacific populations (reviewed in Williams et al [57] Rees et al [58] and Maitland et al [59])

In β-thalassemias excess α-globin chains precipitate in red cell precursors leading to ineffective erythropoi-esis and resulting in anemia in the context of increased iron absorption and iron accumulation The clinical expression of β-thalassemia varies widely depending on the exact genetic lesions inherited and interactions with other genetic loci including the α and γ globin genes β-Thalassemia trait and β-thalassemia interme-diate are often asymptomatic and may not be diagnosed except for mild anemia In α-thalassemia the excess β-chains form stable homotetramers which do not sig-nificantly affect erythropoiesis but cause an increased rate of hemolysis of mature cells The degree of the deficit of α-globin chains depends on the number of α-globin genes inactivated and unless three α-globin genes are lost the effects are subtle and various so that the condition will go largely undiagnosed It might be supposed that iron supplementation could be more deleterious in populations with a high prevalence of β-thalassemia mutations because of the inability to utilize the iron leading to increased iron availability to pathogens or iron-induced oxidant stress Interest-ingly Oppenheimer [2] reported that the increased susceptibility to malaria associated with parenteral iron in Papua New Guinean children was not apparent in

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S534 A M Prentice et al

single-deletion α-thalassemia compared with normal children

In a prospective casendashcontrol study in Papua New Guinea α-thalassemic α+ndash homozygotes and α+ndash heterozygotes had a greatly decreased risk of severe malaria (incidence rate ratio = 04 and 066) compared with controls [9] Furthermore protection was also observed for hospitalization from other infections possibly suggesting an immune component to the pro-tection [60] although the reduction of severe malaria may reduce infectious sequelae by invasive bacte-rial disease In apparent contrast α-thalassemia has also been associated with an increased prevalence of uncomplicated malaria in Vanuatu particularly in very young children with P vivax [57] It was suggested that increased red cell turnover in these children increased susceptibility to P vivax [58] resulting in cross-species immunity to P falciparum in later life [59] A similar finding was reported for glucose-6-phosphate dehy-drogenase (G6PD) deficiency in a cohort study in Uganda in which many other potential risk factors for malarial infection were controlled for (age water source use of prophylaxis bednet usage and proxim-ity to mosquito breeding sites) Female heterozygotes for G6PD had a significantly increased incidence of uncomplicated malaria (IRR = 13 p = 03) and a trend for increased parasite densities similar trends were seen for hemizygote males This was different from the pattern observed for HbS heterozygotes who had a nonsignificantly decreased incidence of uncomplicated malaria and decreased parasite densities [61]

A mechanism that has been suggested for G6PD defi-ciency and that may also be applicable to sickle (HbAS) and thalassemic cells involves decreased oxidative protection (G6PD) or increased constitutive oxidative stress of these cells (HbAS αβ thalassemias) especially when infected resulting in increased clearance of the cells from non-malaria-specific immune mechanisms essentially the same as the normal removal of old ldquosenescentrdquo red cells by phagocytes [62ndash64] It has been proposed that such a mechanism could prevent parasitemias from reaching critically high densities and therefore protect from severe malaria and also facilitate the development of antibody repertoires in children from the maintenance of low-grade infections in young children [65ndash67] In a slight modification of this hypothesis the increased phagocytic removal of early ring-stage infected cellsmdashcompared with schizonts and trophozoitesmdashhas been demonstrated for G6PD β-thalassemic and HbAS cells in vitro but not for α-thalassemic infected cells [68] The phagocytosis of ring compared with later stages may be advantageous since rings contain less hemozoin the buildup of which in monocytes has been associated with decreased func-tion Additionally the reduction of the later stages of parasite development may reduce the development of severe symptoms such as cerebral malaria from

reduced endothelial adhesion of late-stage infected red blood cells to receptors such as intracellular adhesion molecule-1 (ICAM-1)

The epidemiological evidence for a protective effect of HbAS suggests that the protective effects are great-est for severe disease (reviewed by Roberts et al [69]) In the most comprehensive study to date a detailed prospective cohort in two Kenyan populations it was reported that HbS heterozygotes had a significantly decreased risk of mild clinical malaria as assessed by active surveillance (50 decreased risk 95 confi-dence interval [CI] 26 to 67]) a 75 (95 CI 84 to 61) decreased risk of hospital admission for malaria and a 90 [95 CI 3 to 99] decreased risk of severe malaria (severe malarial anemia cerebral malaria or complicated malaria) [70] There was no effect of HbAS on the risk of asymptomatic infec-tions or of parasite density in asymptomatic infections assessed at four cross-sectional surveys There were significant decreases in parasite densities for all of the other categories of infection Additionally in this study unlike another in western Kenya [71] the protection was specific to malaria and did not extend to other common childhood infections including respiratory infections gastroenteritis and helminth infections

What influence the hemoglobinopathic and other polymorphisms may have on the effect of iron sup-plementation on malarial susceptibility is potentially dependent on the extent and mechanisms of protection from infection in the different genotypesmdashinfluences that are likely to be further complicated by differential effects according to age and malarial exposure and effects of coinheritance [72] The coinheritance of the HbS G6PD deficiency and α-thalassemia deletion alle-les is likely to be prevalent in sub-Saharan populations making the study of such effects in real populations extremely difficult by requiring very large sample sizes and complex statistical modeling

To the authorsrsquo knowledge only two published randomized controlled trials of iron supplementation have assessed the effects by genotypemdashin both cases by HbAS versus HbAA [73 74]

In the first trial involving Traditional Birth Attend-ant-administered routine iron supplementation to multigravid Gambian pregnant women Menendez et al [73] reported that although overall there were significant beneficial effects on hemoglobin and packed cell volume (PCV) and on birthweight these effects were entirely accounted for by women with the HbAA phenotype (N = 402 vs N = 98) whereas iron-supplemented HbAS women had lower HB PCV and birthweight than HbAA women receiving placebo Furthermore even in this relatively small study these interactions were statistically significant (p lt 01 for hematological indices at delivery baseline measurements as a covariate p lt 03 for birthweight maternal height included as a covariate) Overall

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S535Iron metabolism and malaria

there was no reported increase in susceptibility to malaria as assessed by the prevalence of peripheral malaria at late pregnancy and delivery or by placental histology Yet iron-supplemented HbAS women had an increased prevalence of placental malaria (76 [2229]) compared with iron-supplemented HbAA women (53 [83158]) placebo-treated HbAA women (59 [91154]) or placebo-treated HbAS women (58 [1933]) At the time of this study IPT prophylaxis was recommended only for primigravid pregnant women in the Gambia hence the choice of the study population What the effects of iron supplementation might be in either primigravidae or multigravidae receiving IPTmdashwhich is now recommended for all pregnant women in malaria-endemic countriesmdashhas not been assessed The protection afforded by the HbAS genotype is likely to vary according to gravidity and malarial endemic-ity In areas of high transmission the majority of the increased risk is borne by primigravidae whereas in areas of lower and highly defined seasonal transmis-sion the increased risk extends to a greater number of pregnancies [75] The protective effect of HbAS is thought to be greatest in relatively nonimmune young children who have not yet developed acquired immunity by exposure to a variety of clonal variants of P falciparum and therefore have not developed a full antibody repertoire to the variant surface antigens (VSA) expressed on the cell surfaces of parasitized red blood cells

In the second trial the effect of the HbAS phenotype on the response to iron supplementation in children was assessed in a subanalysis of a 2 times 2 randomized controlled trial of iron supplementation and inter-mittent preventive treatment (IPT) for malaria using sulfadoxinendashpyrimethamine in anemic Kenyan chil-dren (hemoglobin 7 to 109 gdL) [74] There was no reported increase in the susceptibility to clinical malaria or the prevalence of parasitemia at monthly screening associated with the iron supplementation alone or with IPT [16] whereas IPT plus iron was the most effective in increasing hemoglobin concentrations There were no significant statistical interactions between HbASAA phenotypes and treatment group However there was a nonsignificant increase in the incidence rate ratio of clinical malaria in the HbAS group not receiv-ing IPT during the 12 weeks of follow-up (IRR = 416 95 CI 05 to 346) and increased geometric mean parasite density in both groups but by far the biggest difference was seen in the group receiving IPT (6203 vs 1853 p = 08 for the interaction) The authors acknowledge that the number of clinical events was very small and that these findings would need veri-fication in a larger study since the number of HbAS individuals (approximately 25 to 30) in each treatment group versus approximately 100 HbAA individuals plus the short follow-up time means that the study was grossly underpowered to assess these outcomes If this

effect is real then the age group studied in this trial (2 to 36 months with 78 lt 18 months) should include the most affected although greater effects might be observed in areas of lower transmission and therefore also in a greater age range of children The results of these two trials warrant urgent further trials or retro-spective analysis of prior trials with sufficient power and detail to make firm conclusions on the effects of common polymorphisms on the response to iron sup-plementation which may be expected to vary by age group and transmission intensity

Clinical trials of IPT during infancy (IPTi) have demonstrated a reduction in the prevalence of anemia in young children in malaria-endemic areas [16 18 38 76] and in some trials a reduction in the incidence of clinical malaria [38 76] and morbidity and mortality in the first year of life [38 77] However the effects may vary depending on the timing of dosing choice of drug local levels of resistance and levels of transmission [78 79] On the basis of our analysis above the impact of IPTi plus iron supplementation may be modulated by levels of hemoglobinopathies and therefore suba-nalyses of these studies should be performed according to genotype wherever possible

Interactions of polymorphisms in host iron metabolism and regulatory proteins with malaria

Polymorphisms of haptoglobin a plasma protein that binds free hemoglobin released from lysed red blood cells recirculating the heme portion to the bone marrow through monocyte and macrophage uptake via CD136 have also been associated with malarial outcomes although reports are conflicting Hap-toglobin exists as three common phenotypes Hp1-1 1-2 and 2-2 In case-control studies in India Sudan Ghana and Cameroon the Hp2-2 phenotype has been associated with protection from severe malaria and placental infection [80ndash83] However two studies that have assessed associations with haptoglobin genotypes did not report any associations [84 85] In a cohort study in Gambian children the Hp2-2 genotype was associated with a greater drop in hemoglobin concen-trations across a malarial transmission season [65] The authors proposed that this effect may have been mediated through an increased prevalence of asymp-tomatic infection observed in the Hp2-2 group which contributed to anemia but could provide protection against severe malaria Interestingly similar but smaller drops in hemoglobin concentration were also observed for heterozygotes for G6PD and HbS We are currently analyzing the effects of low-dose iron supplementation during a malarial transmission season in a similar cohort of children

Inducible heme oxygenase (iHO-1) catalyzes the

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S536 A M Prentice et al

breakdown of heme to generate iron carbon monoxide and biliverdin and is expressed in monocytes and mac-rophages among other cells Biliverdin is subsequently degraded to bilirubin which has potent antioxidant effects Microsatellite polymorphisms in the number of tandem repeats in the promoter of iHO-1 have been variously associated with increased and decreased oxidant stress in various disease pathologies However in a case-control study of cerebral malaria patients in Myanmar homozygotes for the short number of repeats (lt 28) previously associated with higher levels of transcription of iHO-1 were significantly more likely to have cerebral malaria than uncomplicated malaria (odds ratio 314 p = 008) [86] It is not clear how this effect may be mediated but it is possible that it results from increased levels of free iron and resulting oxidant stress

In summary the mechanisms by which various genetic polymorphisms interact with malarial infec-tion are still not clear Furthermore it is not clear how they may affect a possible relationship between iron and malaria especially in relation to supplementation which should be differentiated from that of iron status The current evidence suggests that the heterozygous states of the hemoglobinopathies do not protect against malaria by a simple mechanism involving iron with-holding from the pathogen However the effects of iron supplementation in individuals with the most common polymorphisms should be carefully evaluated taking into account differences in transmission intensity and iron status at baseline

Conclusions

The evidence reviewed above tends to substantiate the concerns raised by the recent Pemba trial that universal administration of iron to children in malarious areas may be associated with adverse outcomes The mecha-nism by which this occurs is far from clear and merits

further research to test whether other chemical forms of supplementary iron might carry less risk There is also evidence that the risk profile will be altered by host genetic variations in hemoglobinopathies G6PD and genes regulating iron metabolism However these insights are not of great practical value because population screening and targeted supplementation programs are not feasible in the areas where iron defi-ciency is most prevalent Likewise the evidence that anemic children are probably at low risk for any adverse outcomes associated with iron supplementation implies a need for prescreening that may not be cost-effective or logistically feasible in developing-country settings

The evidence is fairly clear that malaria causes anemia by diverting iron away from bone marrow and erythropoiesis as part of the inflammatory response and hence iron administration alone is not likely to be the most effective means of combating the anemia Other therapeutic paradigms that combat the inflam-mation and adjust the timing of iron administra-tion to children recovering from malaria should be researched

We suggest that further research is still required to confirm the apparent relationships between iron status and malaria and that such studies should also focus on the underlying mechanisms of the putative interaction This might be achieved through the establishment of a multicountry collaboration to standardize protocols both for iron-supplementation interventions and for the assessment of iron and malaria status indicators Standardizing protocols across variations in age groups malaria transmission patterns and genetic distribu-tions of hemoglobinopathies will provide the evidence for a more targeted approach to policies of prevention and treatment of anemia in malaria-endemic regions

Until this evidence is gathered we recommend that iron supplementation in malarious areas must be accompanied by effective systems for ensuring univer-sal rapid access to diagnosis and treatment of malaria or by preventive therapy

References

1 WHO UNICEF Focusing on anaemia Towards an integrated approach for effective anaemia control Joint WHO UNICEF Statement Geneva Joint WHO UNICEF Statement 2004

2 Oppenheimer SJ Iron and its relation to immunity and infectious disease J Nutr 2001131616Sndash33S discussion 33Sndash35S

3 Murray MJ Murray AB Murray NJ Murray MB Diet and cerebral malaria the effect of famine and refeeding Am J Clin Nutr 19783157ndash61

4 Nyakeriga AM Troye-Blomberg M Dorfman JR Alexander ND Back R Kortok M Chemtai AK Marsh K Williams TN Iron deficiency and malaria among children living on the coast of Kenya J Infect Dis 2004 190439ndash47

5 Oppenheimer SJ Macfarlane SB Moody JB Bunari O Hendrickse RG Effect of iron prophylaxis on morbidity due to infectious disease report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 1986 80596ndash602

6 Shipton D Association between haemoglobin level and susceptibility to malaria a study of Gambian children [MSc dissertation] London London School of Hygiene and Tropical Medicine 2004

7 Snow RW Byass P Shenton FC Greenwood BM The relationship between anthropometric measurements and measurements of iron status and susceptibility to malaria in Gambian children Trans R Soc Trop Med Hyg 199185584ndash9

8 Asobayire FS Adou P Davidsson L Cook JD Hurrell

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S537Iron metabolism and malaria

RF Prevalence of iron deficiency with and without concurrent anemia in population groups with high prevalences of malaria and other infections a study in Cote drsquoIvoire Am J Clin Nutr 200174776ndash82

9 Allen SJ OrsquoDonnell A Alexander ND Alpers MP Peto TE Clegg JB Weatherall DJ alpha+-Thalassemia protects children against disease caused by other infec-tions as well as malaria Proc Natl Acad Sci U S A 1997 9414736ndash41

10 Murray MJ Murray AB Murray MB Murray CJ The adverse effect of iron repletion on the course of certain infections Br Med J 197821113ndash5

11 Smith AW Hendrickse RG Harrison C Hayes RJ Greenwood BM The effects on malaria of treatment of iron-deficiency anaemia with oral iron in Gambian children Ann Trop Paediatr 1989917ndash23

12 Oppenheimer SJ Gibson FD Macfarlane SB Moody JB Harrison C Spencer A Bunari O Iron supplementation increases prevalence and effects of malaria report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 198680603ndash12

13 Byles AB Drsquosa A Reduction of reaction due to iron dextran infusion using chloroquine Br Med J 19703625ndash7

14 Berger J Dyck JL Galan P Aplogan A Schneider D Traissac P Hercberg S Effect of daily iron supplementa-tion on iron status cell-mediated immunity and inci-dence of infections in 6ndash36 month old Togolese children Eur J Clin Nutr 20005429ndash35

15 Chippaux JP Schneider D Aplogan A Dyck JL Berger J [Effects of iron supplementation on malaria infection] Bull Soc Pathol Exot 19918454ndash62

16 Desai MR Mei JV Kariuki SK Wannemuehler KA Phil-lips-Howard PA Nahlen BL Kager PA Vulule JM ter Kuile FO Randomized controlled trial of daily iron sup-plementation and intermittent sulfadoxine-pyrimeth-amine for the treatment of mild childhood anemia in western Kenya J Infect Dis 2003187658ndash66

17 Nwanyanwu OC Ziba C Kazembe PN Gamadzi G Gandwe J Redd SC The effect of oral iron therapy during treatment for Plasmodium falciparum malaria with sulphadoxine-pyrimethamine on Malawian chil-dren under 5 years of age Ann Trop Med Parasitol 199690589ndash95

18 Verhoef H West CE Nzyuko SM de Vogel S van der Valk R Wanga MA Kuijsten A Veenemans J Kok FJ Intermittent administration of iron and sulfadoxine-py-rimethamine to control anaemia in Kenyan children a randomised controlled trial Lancet 2002360908ndash14

19 van den Hombergh J Dalderop E Smit Y Does iron therapy benefit children with severe malaria-associated anaemia A clinical trial with 12 weeks supplementation of oral iron in young children from the Turiani Division Tanzania J Trop Pediatr 199642220ndash7

20 Lawless JW Latham MC Stephenson LS Kinoti SN Pertet AM Iron supplementation improves appetite and growth in anemic Kenyan primary school children J Nutr 1994124645ndash54

21 Mebrahtu T Stoltzfus RJ Chwaya HM Jape JK Savioli L Montresor A Albonico M Tielsch JM Low-dose daily iron supplementation for 12 months does not increase the prevalence of malarial infection or den-sity of parasites in young Zanzibari children J Nutr 20041343037ndash41

22 Menendez C Kahigwa E Hirt R Vounatsou P Aponte JJ Font F Acosta CJ Schellenberg DM Galindo CM Kimario J Urassa H Brabin B Smith TA Kitua AY Tanner M Alonso PL Randomised placebo-controlled trial of iron supplementation and malaria chemoproph-ylaxis for prevention of severe anaemia and malaria in Tanzanian infants Lancet 1997350844ndash50

23 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S MrsquoBoge B Greenwood BM The effects of iron supplementation during pregnancy given by traditional birth attendants on the prevalence of anaemia and malaria Trans R Soc Trop Med Hyg 199488590ndash3

24 van Hensbroek MB Morris-Jones S Meisner S Jaffar S Bayo L Dackour R Phillips C Greenwood BM Iron but not folic acid combined with effective antimalarial therapy promotes haematological recovery in African children after acute falciparum malaria Trans R Soc Trop Med Hyg 199589672ndash6

25 Sazawal S Black RE Ramsan M Chwaya HM Stoltzfus RJ Dutta A Dhingra U Kabole I Deb S Othman MK Kabole FM Effects of routine prophylactic supplemen-tation with iron and folic acid on admission to hospital and mortality in preschool children in a high malaria transmission setting community-based randomised placebo-controlled trial Lancet 2006367133ndash43

26 Harvey PW Heywood PF Nesheim MC Galme K Zegans M Habicht JP Stephenson LS Radimer KL Brabin B Forsyth K et al The effect of iron therapy on malarial infection in Papua New Guinean schoolchil-dren Am J Trop Med Hyg 19894012ndash8

27 Andrews NC Iron homeostasis insights from genetics and animal models Nat Rev Genet 20001208ndash17

28 Kristiansen M Graversen JH Jacobsen C Sonne O Hoffman HJ Law SK Moestrup SK Identification of the haemoglobin scavenger receptor Nature 2001409 198ndash201

29 Wickramasinghe SN Abdalla SH Blood and bone marrow changes in malaria Baillieres Best Pract Res Clin Haematol 200013277ndash99

30 Phillips RE Looareesuwan S Warrell DA Lee SH Karbwang J Warrell MJ White NJ Swasdichai C Weatherall DJ The importance of anaemia in cerebral and uncomplicated falciparum malaria role of compli-cations dyserythropoiesis and iron sequestration Q J Med 198658305ndash23

31 Abdalla S Weatherall DJ Wickramasinghe SN Hughes M The anaemia of P falciparum malaria Br J Haematol 198046171ndash83

32 Sen R Bhatnagar BM Singh U Yadav MS Sehgal PK Patterns of erythropoiesis and anaemia in malaria J Commun Dis 199022247ndash53

33 Srichaikul T Wasanasomsithi M Poshyachinda V Panikbutr N Rabieb T Ferrokinetic studies and eryth-ropoiesis in malaria Arch Intern Med 1969124623ndash8

34 Das BS Thurnham DI Das DB Influence of malaria on markers of iron status in children implications for interpreting iron status in malaria-endemic communi-ties Br J Nutr 199778751ndash60

35 Menendez C Quinto LL Kahigwa E Alvarez L Fern-andez R Gimenez N Schellenberg D Aponte JJ Tanner M Alonso PL Effect of malaria on soluble transferrin receptor levels in Tanzanian infants Am J Trop Med Hyg 200165138ndash42

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S538 A M Prentice et al

36 Stoltzfus RJ Chwaya HM Montresor A Albonico M Savioli L Tielsch JM Malaria hookworms and recent fever are related to anemia and iron status indicators in 0- to 5-y old Zanzibari children and these relationships change with age J Nutr 20001301724ndash33

37 Stoltzfus RJ Chwaya HM Albonico M Schulze KJ Savioli L Tielsch JM Serum ferritin erythrocyte pro-toporphyrin and hemoglobin are valid indicators of iron status of school children in a malaria-holoendemic population J Nutr 1997127293ndash8

38 Massaga JJ Kitua AY Lemnge MM Akida JA Malle LN Ronn AM Theander TG Bygbjerg IC Effect of intermittent treatment with amodiaquine on anaemia and malarial fevers in infants in Tanzania a randomised placebo-controlled trial Lancet 20033611853ndash60

39 Verhoef H West CE Kraaijenhagen R Nzyuko SM King R Mbandi MM van Laatum S Hogervorst R Schep C Kok FJ Malarial anemia leads to adequately increased erythropoiesis in asymptomatic Kenyan children Blood 20021003489ndash94

40 Stoltzfus RJ Chway HM Montresor A Tielsch JM Jape JK Albonico M Savioli L Low dose daily iron supplementation improves iron status and appetite but not anemia whereas quarterly anthelminthic treatment improves growth appetite and anemia in Zanzibari preschool children J Nutr 2004134348ndash56

41 Kurtzhals JA Addae MM Akanmori BD Dunyo S Koram KA Appawu MA Nkrumah FK Hviid L Anae-mia caused by asymptomatic Plasmodium falciparum infection in semi-immune African schoolchildren Trans R Soc Trop Med Hyg 199993623ndash7

42 Loyevsky M John C Dickens B Hu V Miller JH Gordeuk VR Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators Mol Biochem Parasitol 199910143ndash59

43 Scholl PF Tripathi AK Sullivan DJ Bioavailable iron and heme metabolism in Plasmodium falciparum Curr Top Microbiol Immunol 2005295293ndash324

44 Darbari D Loyevsky M Gordeuk V Kark JA Castro O Rana S Apprey V Kurantsin-Mills J Fluorescence meas-urements of the labile iron pool of sickle erythrocytes Blood 2003102357ndash64

45 Ginsburg H Iron acquisition by Plasmodium spp Para-sitol Today 199915466

46 Atamna H Ginsburg H Heme degradation in the presence of glutathione A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells J Biol Chem 199527024876ndash83

47 Gabay T Ginsburg H Hemoglobin denaturation and iron release in acidified red blood cell lysatemdasha possible source of iron for intraerythrocytic malaria parasites Exp Parasitol 199377261ndash72

48 Iyer JK Shi L Shankar AH Sullivan DJ Jr Zinc pro-toporphyrin IX binds heme crystals to inhibit the proc-ess of crystallization in Plasmodium falciparum Mol Med 20039175ndash82

49 Cabantchik ZI Moody-Haupt S Gordeuk VR Iron che-lators as anti-infectives malaria as a paradigm FEMS Immunol Med Microbiol 199926289ndash98

50 Hershko C Control of disease by selective iron deple-tion a novel therapeutic strategy utilizing iron chelators Baillieres Clin Haematol 19947965ndash1000

51 Pradines B Tall A Ramiandrasoa F Spiegel A Sokhna C Fusai T Mosnier J Daries W Trape JF Kunesch G Parzy D Rogier C In vitro activity of iron-binding compounds against Senegalese isolates of Plasmodium falciparum J Antimicrob Chemother 2006571093ndash9

52 Meshnick SR Yang YZ Lima V Kuypers F Kam-chonwongpaisan S Yuthavong Y Iron-dependent free radical generation from the antimalarial agent artem-isinin (qinghaosu) Antimicrob Agents Chemother 1993371108ndash14

53 Golenser J Domb A Mordechai-Daniel T Leshem B Luty A Kremsner P Iron chelators correlation between effects on Plasmodium spp and immune functions J Parasitol 200692170ndash7

54 Nyakeriga AM Williams TN Marsh K Wambua S Perlmann H Perlmann P Grandien A Troye-Blomberg M Cytokine mRNA expression and iron status in chil-dren living in a malaria endemic area Scand J Immunol 200561370ndash5

55 Smith HJ Meremikwu M Iron chelating agents for treating malaria Cochrane Database Syst Rev 2003CD001474

56 Weatherall DJ The global problem of genetic disease Ann Hum Biol 200532117ndash22

57 Williams TN Maitland K Bennett S Ganczakowski M Peto TE Newbold CI Bowden DK Weatherall DJ Clegg JB High incidence of malaria in alpha-thalassaemic children Nature 1996383522ndash5

58 Rees DC Williams TN Maitland K Clegg JB Weather-all DJ Alpha thalassaemia is associated with increased soluble transferrin receptor levels Br J Haematol 1998103365ndash9

59 Maitland K Williams TN Bennett S Newbold CI Peto TE Viji J Timothy R Clegg JB Weatherall DJ Bowden DK The interaction between Plasmodium falciparum and P vivax in children on Espiritu Santo island Van-uatu Trans R Soc Trop Med Hyg 199690614ndash20

60 Weatherall DJ Clegg JB Genetic variability in response to infection malaria and after Genes Immun 2002 3331ndash7

61 Parikh S Dorsey G Rosenthal PJ Host polymorphisms and the incidence of malaria in Ugandan children Am J Trop Med Hyg 200471750ndash3

62 Destro Bisol G Genetic resistance to malaria oxidative stress and hemoglobin oxidation Parassitologia 1999 41203ndash4

63 Cappadoro M Giribaldi G OrsquoBrien E Turrini F Mannu F Ulliers D Simula G Luzzatto L Arese P Early phago-cytosis of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes parasitized by Plasmodium falciparum may explain malaria protection in G6PD deficiency Blood 1998922527ndash34

64 Arese P Turrini F Schwarzer E Band 3complement-mediated recognition and removal of normally senes-cent and pathological human erythrocytes Cell Physiol Biochem 200516133ndash46

65 Atkinson SH Rockett K Sirugo G Bejon PA Fulford A OrsquoConnell M A Bailey R Kwiatkowski DP Prentice AM Seasonal Childhood Anaemia in West Africa Is Associated with the Haptoglobin 2-2 Genotype PLoS Med 20063e172

66 Cabrera G Cot M Migot-Nabias F Kremsner PG Deloron P Luty AJ The sickle cell trait is associated

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S539Iron metabolism and malaria

with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens J Infect Dis 20051911631ndash8

67 Williams TN Mwangi TW Roberts DJ Alexander ND Weatherall DJ Wambua S Kortok M Snow RW Marsh K An immune basis for malaria protection by the sickle cell trait PLoS Med 20052e128

68 Ayi K Turrini F Piga A Arese P Enhanced phagocyto-sis of ring-parasitized mutant erythrocytes a common mechanism that may explain protection against falci-parum malaria in sickle trait and beta-thalassemia trait Blood 20041043364ndash71

69 Roberts DJ Harris T Williams T The influence of inherited traits on malaria infection In Bellamy R ed Susceptibility to infectious diseases the importance of host genetics Cambridge Cambridge University Press 2004 139ndash84

70 Williams TN Mwangi TW Wambua S Alexander ND Kortok M Snow RW Marsh K Sickle cell trait and the risk of Plasmodium falciparum malaria and other child-hood diseases J Infect Dis 2005192178ndash86

71 Aidoo M Terlouw DJ Kolczak MS McElroy PD ter Kuile FO Kariuki S Nahlen BL Lal AA Udhayakumar V Protective effects of the sickle cell gene against malaria morbidity and mortality Lancet 20023591311ndash2

72 Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K Nega-tive epistasis between the malaria-protective effects of alpha+-thalassemia and the sickle cell trait Nat Genet 2005371253ndash7

73 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S Ascaso C Smith T MrsquoBoge B Greenwood BM The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS Trans R Soc Trop Med Hyg 199589289ndash92

74 Terlouw DJ Desai MR Wannemuehler KA Kariuki SK Pfeiffer CM Kager PA Shi YP Ter Kuile FO Relation between the response to iron supplementation and sickle cell hemoglobin phenotype in preschool children in western Kenya Am J Clin Nutr 200479466ndash72

75 Duffy PE Fried M Malaria in the pregnant woman Curr Top Microbiol Immunol 2005295169ndash200

76 Schellenberg D Menendez C Kahigwa E Aponte J Vidal J Tanner M Mshinda H Alonso P Intermittent treatment for malaria and anaemia control at time of routine vaccinations in Tanzanian infants a randomised placebo-controlled trial Lancet 20013571471ndash7

77 Schellenberg D Menendez C Aponte JJ Kahigwa E Tanner M Mshinda H Alonso P Intermittent preventive antimalarial treatment for Tanzanian infants follow-up to age 2 years of a randomised placebo-controlled trial Lancet 20053651481ndash3

78 OrsquoMeara WP Breman JG McKenzie FE The promise and potential challenges of intermittent preventive treat-ment for malaria in infants (IPTi) Malar J 2005433

79 White NJ Intermittent presumptive treatment for malaria PLoS Med 20052e3

80 Elagib AA Kider AO Akerstrom B Elbashir MI Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan Trans R Soc Trop Med Hyg 199892309ndash11

81 Minang JT Gyan BA Anchang JK Troye-Blomberg M Perlmann H Achidi EA Haptoglobin phenotypes and malaria infection in pregnant women at delivery in western Cameroon Acta Trop 200490107ndash14

82 Quaye IK Ekuban FA Goka BQ Adabayeri V Kurtzhals JA Gyan B Ankrah NA Hviid L Akanmori BD Hap-toglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria Trans R Soc Trop Med Hyg 200094216ndash9

83 Singh IP Walter H Bhasin MK Bhardwaj V Sudhakar K Genetic markers and malaria Observations in Gujarat India Hum Hered 19863631ndash6

84 Aucan C Walley AJ Greenwood BM Hill AV Hap-toglobin genotypes are not associated with resistance to severe malaria in The Gambia Trans R Soc Trop Med Hyg 200296327ndash8

85 Bienzle U Eggelte TA Adjei LA Dietz E Ehrhardt S Cramer JP Otchwemah RN Mockenhaupt FP Limited influence of haptoglobin genotypes on severe malaria in Ghanaian children Trop Med Int Health 200510668ndash71

86 Takeda M Kikuchi M Ubalee R Na-Bangchang K Ruangweerayut R Shibahara S Imai S Hirayama K Microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with susceptibility to cerebral malaria in Myanmar Jpn J Infect Dis 2005 58268ndash71

87 Shankar AH Nutritional modulation of malaria mor-bidity and mortality J Infect Dis 2000182 Suppl 1 S37ndash53

88 Gera T Sachdev HP Effect of iron supplementation on incidence of infectious illness in children systematic review Bmj 20023251142

Page 8: Iron metabolism and malaria

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S531Iron metabolism and malaria

(IPT) practices influence population immunity and resultant malarial clinical presentation as well as the epidemiology of anemia in a particular setting These factors may also influence the disturbance of iron metabolism and erythropoietic response to iron sup-plementation Acute malaria is associated predomi-nantly with a picture of fever hemolysis and oxidant stress whereas dyserythropoiesis predominates in the anemia of chronic malaria in a semiimmune patient [29] Acute malarial hemolysis represents a major stress on the homeostatic mechanisms of iron flux regulation that have evolved primarily to maintain erythroblast supply while minimizing the oxidant stress-associated effects of iron

Iron can be sequestered and trapped in reticuloen-dothelial macrophages as a result of both chronic and acute malaria and can present a picture of iron-deficient erythropoiesis associated with normal or increased bone marrow iron For instance bone marrow aspirates in 23 Thai patients with uncomplicated acute malaria (age 15 to 52 years) demonstrated malarial pigment in 22 of them Convalescent bone marrow aspirates in 16 patients (3 to 25 days after admission) demonstrated increased iron content compared with the admission sample [30] Five of six Gambian children (lt 5 years of age) with acute malaria had elevated stainable bone marrow iron and four of six children with chronic malaria and severe anemia (hemoglobin lt 6 gdL) had either normal or markedly increased levels of bone marrow stainable iron [31] Eighty-six percent of Indian children and adults (N = 26) with acute and 84 of those with chronic falciparum malaria and anemia (mean hemoglobin 54 gdL N = 38) had normal or increased bone marrow iron stores [32] Ferrokinetic studies involving the intravenous administration of 59Fe demonstrated low unsaturated iron-binding capacity and a rapid plasma iron disappearance time in both parasitemic and postparasitemic patients with acute and secondary (recent acute infection with persistent parasitemia) P falciparum and P vivax in Thai adults compared with controls [33] Incorporation of 59Fe into red blood cells was decreased in acute (N = 5) and secondary parasitemia (11 of 14) but found to be largely normal in the postparasitemic patients includ-ing 3 who were restudied from the parasitemic group Iron sequestration in acute malaria is cytokine driven (elevated tumor necrosis factor α [TNF-α] ILndash1 and interferon γ [IFN-γ] and diminished ILndash10) [29] prob-ably mediated via hepcidin however quantifying this phenomenon assessing how long it persists after acute malaria and in association with chronic malaria and assessing its importance in relation to malarial anemia malaria-associated immunosuppression and response to iron supplementation is difficult since there are few data Conventional indices of iron storage (eg ferritin) or of tissue supply (eg zinc protoporphyrin soluble transferrin receptor transferrin saturation) are

affected by inflammation [8 34ndash36] and the assess-ment of the iron status of young children in malarious areas with acute or chronic malaria is problematic [34] In a holoendemic environment ferritin and eryth-rocyte protoporphyrin were not affected by chronic malaria in older children [37] These indices also do not distinguish between iron deficiency and iron sequestration

Effect of malaria on response to iron supplementation

Malaria-induced anemia does not lead to loss of iron from the body However iron deficiency often coex-ists with malaria in areas of malaria transmission and therapy for severe postmalarial anemia commonly assumes a component due to preexisting iron defi-ciency Iron supplements are routinely prescribed both for severe malaria-associated anemia and for presumed iron-deficient anemia in a malaria-endemic environ-ment Few studies however have looked at the effect of acute malaria on the response to iron supplementation and even fewer have addressed the effect of chronic asymptomatic malaria More commonly studies either have either assessed the response to supplementation of children with anemia of undefined etiology in areas of coexistent malaria iron deficiency and hookworm or have randomized children who were anemic after malaria to a variety of hematinics In a study of 222 Malawian children (lt 5 years of age) with anemia after acute malaria the use of Fansidar and daily supplemen-tal iron resulted in a significantly greater hemoglobin recovery than Fansidar alone or Fansidar and weekly iron only in those children with initial hemoglobin between 5 and 8 gdL [17] However a larger propor-tion of the iron-treated children failed to clear their malaria In the Gambia 600 children (mean age 52 months mean hemoglobin 96 gdL) with uncompli-cated falciparum malaria randomized to receive chlo-roquine or Fansidar as treatment and then either iron folic acid or placebo for 28 days [22] demonstrated a significantly better hemoglobin response with iron than with placebo or folic acid (the difference in mean hemoglobin level after 1 month was 07 gdL) One hundred Tanzanian children (lt 30 months of age) with severe anemia (hemoglobin lt 5 gdL) were randomized either to receive daily iron supplementation or to be controls after antimalarial treatment [19] Among the 60 who completed the 12-week follow-up without a transfusion (30 in each group) there were no differ-ences in hemoglobin recovery From these studies the role of iron supplementation in the treatment of anemia after acute malaria is unclear and it is likely that the hemoglobin response to supplementation is influenced by both the direct inflammatory effect of malaria on iron absorption and utilization and preexistent iron

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S532 A M Prentice et al

deficiency which is impossible to assess in the presence of malaria In the Gambia we recently compared the absorption of stable-isotope-labeled iron in children anemic as a result of iron deficiency and children anemic after acute malaria Both groups were given 30 days of iron supplementation and the malaria group demonstrated significantly better hemoglobin recovery despite initially significantly reduced iron absorption (Doherty et al unpublished results) Utilization of sequestered iron is likely to be a major contributor to erythroblastic iron requirement after acute malaria

Studies of iron supplementation of populations of anemic children in malarious areas have reported either improved hemoglobin response or decreased prevalence of severe anemia [16 22 38 39] Incorpo-ration of antimalarial intervention arms is common Malaria transmission characteristics study design use of antecedent antimalarials differing iron supplemen-tation doses and differing outcome measures as well as different prevalence rates of iron deficiency and hook-worm infection have made the assessment of factors affecting hemoglobin response to iron supplementation difficult In particular the effect of chronic malaria on response to supplementation in high-transmission areas is unclear as the etiology of the anemia and the chronicity of malaria parasitemia are often undefined in study subjects In an area of intense transmission in Tanzania in which more than 80 of children (4 to 71 months old) were parasitemic at baseline and where malaria infection was strongly associated with hemo-globin supplementation improved the iron status and motor and language development of an iron-deficient population but not did not improve hemoglobin [21 36 40] The authors concluded that factors including malarial parasitemia or ineffective erythropoiesis due to inflammatory processes in a population with high levels of infectious morbidity and inflammation might have limited erythropoiesis

An inflammatory-mediated block to iron absorp-tion and utilization is likely to limit the erythropoietic response to supplemental iron after acute malaria how-ever it is unclear whether chronic parasitemia similarly limits the response to supplemental iron The asso-ciation of chronic malaria with anemia [39] stainable bone marrow iron [34] and increased cytokine levels [41] might suggest a probable effect and the eradica-tion of parasites has been associated with hemoglobin improvement without supplemental iron [31]

Iron metabolism by malaria parasites

In this section we consider whether the availability of iron in the host could modulate the efficiency with which malaria parasites can establish an infection and the severity of that infection What evidence is there to support the ldquonutritional immunityrdquo hypothesis that

host iron availability could limit parasite invasion or multiplication andor the clinical sequelae of para-site infection Support for the nutritional immunity hypothesis first stated in the 1970s has generally waned for the majority of pathogens [2] but there may still be a case for obligate intracellular pathogensmdashincluding Plasmodium spp

It may be informative to examine the research of other scientists than those typically involved in the cur-rent debate For example in order for this hypothesis to be truemdashat least in terms of the success of parasite invasion and replicationmdashit is a requirement that P falciparum be dependent on host iron sources for its survival Next is iron deficiency ever likely to be a limiting factor in the supply of iron to the parasite The most recent research suggests that P falciparum does utilize iron from the host but not from the abundant supplies available in erythrocyte hemoglobin the heme portion of which is quickly degraded to nontoxic but non-iron-bioavailable hemozoin or from the plasma via transferrin but from another source possibly an intraerythrocytic labile pool of ferrous iron [42 43] Interestingly measurements of this labile ferrous iron in normal and sickled erythrocytes indicate it to be positively associated with hemoglobin concentrations and negatively associated with plasma ferritin [44] However other researchers have reported evidence to suggest that the degradation of heme to hemozoin is incomplete and that 50 of heme may be degraded via an alternative pathway involving reduced glutathione and releasing bioavailable iron [45 46] As it has been estimated that less than 1 of heme iron would be sufficient to meet parasite iron requirements [47] iron deficiency would never induce iron-limited growth if hemoglobin were the iron source for parasites

Another mechanism by which iron deficiency may limit parasite growth is that proposed recently by Iyer et al [48] who demonstrated the inhibition of hemozoin formation from toxic free heme by the naturally occur-ring zinc protoporphyrin IX (ZPP) at levels likely to be encountered in anemic erythrocytes It is interesting to note that this is thought to be the mechanism by which the quinoline antimalarials act Furthermore Iyer et al demonstrated that quinolines competed for ZPP bind-ing and prevention of hemozoin formation It is pos-sible that via this mechanism moderate anemia could allow the persistence of low levels of parasitemia and therefore affect the development of exposure-related antibody repertoire and clinical immunitymdashwith consequent effects on future malarial incidence and malaria-associated anemia However the evidence for such an effect in human populations is currently limited due to the lack of longitudinal studies assessing ZPP levels and parasite prevalence and density from infancy onwards

Another research area that has been used to support the hypothesis of decreased iron availability is that

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S533Iron metabolism and malaria

of the effects of iron chelators on parasite growth in vitro and in vivo [49 50] Furthermore some antima-larial drugs such as the antibiotic cyclines including doxycycline are also iron chelators However iron chelators may not be acting by depriving the parasite of iron Alternative mechanisms have been suggested for some chelators including the induction of reactive oxygen species from dissociation of iron from heme and hemozoin as suggested for the lipophilic FR160 [51] similar to the suggested mechanism of artemisinin [52] Furthermore differences between the efficacy of chelators in vitro and in vivo have been associated with differences in immune modulation [53] This may suggest that iron status could affect malarial outcomes via direct effects on immune modulation as suggested by Nyakeriga et al [54] The evidence base for the effects of current iron-chelator therapies in reducing the prevalence density or clinical sequelae of malaria is weakmdashas outlined in a recent Cochrane review of clinical trials involving the use of either desferioxamine or the orally available deferiprone [55] in which all of the seven studies included had limitations relat-ing to study size relevance of study populations and more critically methodological and analytical faults However the authors of this review concluded that the results suggested possible benefits of treatment in cerebral malaria with a shorter recovery time from coma and decreased time to parasite clearance The initial justification for using iron-chelator therapy in cerebral malaria was based on the premise of prevent-ing iron-induced damage to brain cells resulting from hemolysis Therefore it is important to note that the possible benefits of iron-chelator therapy may not relate to limitation of iron for parasite growth and may there-fore not provide evidence in support of the nutritional immunity hypothesis

Iron malaria and hemoglobinopathies

How do hemoglobinopathies protect against parasite invasion or multiplication andor clinical sequelae of parasite infection Are these polymorphisms likely to affect the relationship between iron status or supple-mentation and malaria

J B S Haldane is credited with first postulat-ing heterozygote selection as an explanation for the high prevalence of the thalassemias and later other hemoglobinopathies He suggested that the small size reduced hemoglobin concentrations and increased resistance to hypertonic solutions of such cells may result in decreased parasite invasion or growth Although this hypothesis has been widely accepted for some time it has only recently been possible to dem-onstrate that these mutations have been maintained by selection mostly by malaria but possibly also other infectious causes However the extent and mechanisms

of protection are still debated At least in vitro many studies have failed to demonstrate decreased ability of parasites to invade or grow in thalassemic cells or cells containing hemoglobin S (HbS) Instead the mecha-nisms appear to be more complicated and possibly to vary between local conditions

The common polymorphisms involved in hemo-globin synthesis or red cell formation include sickle hemoglobin (HbS) HbC and HbE the α and β-thalassemias and South Asian ovalocytosis The geographic distribution of these varies across tropi-cal areas and can vary extensively even within closely related regions Current estimates of these polymor-phisms are often based on single sites and are likely to be underestimates [56] but a figure of 27 million carriers of the main hemoglobinopathies has been proposed [56] The carrier frequency for HbS is esti-mated at between 5 and 40 in populations across sub-Saharan Africa the Middle East and parts of South Asia HbC is limited to parts of West and North Africa whereas HbE is common in some parts of India and Southeast Asia with carrier rates up to 60 The thalassemias have the broadest geographic distribution and also the widest range of causative mutations and clinical outcomes The carrier frequencies for the more severe range of β-thalassemias is generally lower than for the α-thalassemias which are estimated to reach carrier frequencies of up to 20 in sub-Saharan Africa higher in Middle Eastern and Indian populations and up to 80 in some Pacific populations (reviewed in Williams et al [57] Rees et al [58] and Maitland et al [59])

In β-thalassemias excess α-globin chains precipitate in red cell precursors leading to ineffective erythropoi-esis and resulting in anemia in the context of increased iron absorption and iron accumulation The clinical expression of β-thalassemia varies widely depending on the exact genetic lesions inherited and interactions with other genetic loci including the α and γ globin genes β-Thalassemia trait and β-thalassemia interme-diate are often asymptomatic and may not be diagnosed except for mild anemia In α-thalassemia the excess β-chains form stable homotetramers which do not sig-nificantly affect erythropoiesis but cause an increased rate of hemolysis of mature cells The degree of the deficit of α-globin chains depends on the number of α-globin genes inactivated and unless three α-globin genes are lost the effects are subtle and various so that the condition will go largely undiagnosed It might be supposed that iron supplementation could be more deleterious in populations with a high prevalence of β-thalassemia mutations because of the inability to utilize the iron leading to increased iron availability to pathogens or iron-induced oxidant stress Interest-ingly Oppenheimer [2] reported that the increased susceptibility to malaria associated with parenteral iron in Papua New Guinean children was not apparent in

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S534 A M Prentice et al

single-deletion α-thalassemia compared with normal children

In a prospective casendashcontrol study in Papua New Guinea α-thalassemic α+ndash homozygotes and α+ndash heterozygotes had a greatly decreased risk of severe malaria (incidence rate ratio = 04 and 066) compared with controls [9] Furthermore protection was also observed for hospitalization from other infections possibly suggesting an immune component to the pro-tection [60] although the reduction of severe malaria may reduce infectious sequelae by invasive bacte-rial disease In apparent contrast α-thalassemia has also been associated with an increased prevalence of uncomplicated malaria in Vanuatu particularly in very young children with P vivax [57] It was suggested that increased red cell turnover in these children increased susceptibility to P vivax [58] resulting in cross-species immunity to P falciparum in later life [59] A similar finding was reported for glucose-6-phosphate dehy-drogenase (G6PD) deficiency in a cohort study in Uganda in which many other potential risk factors for malarial infection were controlled for (age water source use of prophylaxis bednet usage and proxim-ity to mosquito breeding sites) Female heterozygotes for G6PD had a significantly increased incidence of uncomplicated malaria (IRR = 13 p = 03) and a trend for increased parasite densities similar trends were seen for hemizygote males This was different from the pattern observed for HbS heterozygotes who had a nonsignificantly decreased incidence of uncomplicated malaria and decreased parasite densities [61]

A mechanism that has been suggested for G6PD defi-ciency and that may also be applicable to sickle (HbAS) and thalassemic cells involves decreased oxidative protection (G6PD) or increased constitutive oxidative stress of these cells (HbAS αβ thalassemias) especially when infected resulting in increased clearance of the cells from non-malaria-specific immune mechanisms essentially the same as the normal removal of old ldquosenescentrdquo red cells by phagocytes [62ndash64] It has been proposed that such a mechanism could prevent parasitemias from reaching critically high densities and therefore protect from severe malaria and also facilitate the development of antibody repertoires in children from the maintenance of low-grade infections in young children [65ndash67] In a slight modification of this hypothesis the increased phagocytic removal of early ring-stage infected cellsmdashcompared with schizonts and trophozoitesmdashhas been demonstrated for G6PD β-thalassemic and HbAS cells in vitro but not for α-thalassemic infected cells [68] The phagocytosis of ring compared with later stages may be advantageous since rings contain less hemozoin the buildup of which in monocytes has been associated with decreased func-tion Additionally the reduction of the later stages of parasite development may reduce the development of severe symptoms such as cerebral malaria from

reduced endothelial adhesion of late-stage infected red blood cells to receptors such as intracellular adhesion molecule-1 (ICAM-1)

The epidemiological evidence for a protective effect of HbAS suggests that the protective effects are great-est for severe disease (reviewed by Roberts et al [69]) In the most comprehensive study to date a detailed prospective cohort in two Kenyan populations it was reported that HbS heterozygotes had a significantly decreased risk of mild clinical malaria as assessed by active surveillance (50 decreased risk 95 confi-dence interval [CI] 26 to 67]) a 75 (95 CI 84 to 61) decreased risk of hospital admission for malaria and a 90 [95 CI 3 to 99] decreased risk of severe malaria (severe malarial anemia cerebral malaria or complicated malaria) [70] There was no effect of HbAS on the risk of asymptomatic infec-tions or of parasite density in asymptomatic infections assessed at four cross-sectional surveys There were significant decreases in parasite densities for all of the other categories of infection Additionally in this study unlike another in western Kenya [71] the protection was specific to malaria and did not extend to other common childhood infections including respiratory infections gastroenteritis and helminth infections

What influence the hemoglobinopathic and other polymorphisms may have on the effect of iron sup-plementation on malarial susceptibility is potentially dependent on the extent and mechanisms of protection from infection in the different genotypesmdashinfluences that are likely to be further complicated by differential effects according to age and malarial exposure and effects of coinheritance [72] The coinheritance of the HbS G6PD deficiency and α-thalassemia deletion alle-les is likely to be prevalent in sub-Saharan populations making the study of such effects in real populations extremely difficult by requiring very large sample sizes and complex statistical modeling

To the authorsrsquo knowledge only two published randomized controlled trials of iron supplementation have assessed the effects by genotypemdashin both cases by HbAS versus HbAA [73 74]

In the first trial involving Traditional Birth Attend-ant-administered routine iron supplementation to multigravid Gambian pregnant women Menendez et al [73] reported that although overall there were significant beneficial effects on hemoglobin and packed cell volume (PCV) and on birthweight these effects were entirely accounted for by women with the HbAA phenotype (N = 402 vs N = 98) whereas iron-supplemented HbAS women had lower HB PCV and birthweight than HbAA women receiving placebo Furthermore even in this relatively small study these interactions were statistically significant (p lt 01 for hematological indices at delivery baseline measurements as a covariate p lt 03 for birthweight maternal height included as a covariate) Overall

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S535Iron metabolism and malaria

there was no reported increase in susceptibility to malaria as assessed by the prevalence of peripheral malaria at late pregnancy and delivery or by placental histology Yet iron-supplemented HbAS women had an increased prevalence of placental malaria (76 [2229]) compared with iron-supplemented HbAA women (53 [83158]) placebo-treated HbAA women (59 [91154]) or placebo-treated HbAS women (58 [1933]) At the time of this study IPT prophylaxis was recommended only for primigravid pregnant women in the Gambia hence the choice of the study population What the effects of iron supplementation might be in either primigravidae or multigravidae receiving IPTmdashwhich is now recommended for all pregnant women in malaria-endemic countriesmdashhas not been assessed The protection afforded by the HbAS genotype is likely to vary according to gravidity and malarial endemic-ity In areas of high transmission the majority of the increased risk is borne by primigravidae whereas in areas of lower and highly defined seasonal transmis-sion the increased risk extends to a greater number of pregnancies [75] The protective effect of HbAS is thought to be greatest in relatively nonimmune young children who have not yet developed acquired immunity by exposure to a variety of clonal variants of P falciparum and therefore have not developed a full antibody repertoire to the variant surface antigens (VSA) expressed on the cell surfaces of parasitized red blood cells

In the second trial the effect of the HbAS phenotype on the response to iron supplementation in children was assessed in a subanalysis of a 2 times 2 randomized controlled trial of iron supplementation and inter-mittent preventive treatment (IPT) for malaria using sulfadoxinendashpyrimethamine in anemic Kenyan chil-dren (hemoglobin 7 to 109 gdL) [74] There was no reported increase in the susceptibility to clinical malaria or the prevalence of parasitemia at monthly screening associated with the iron supplementation alone or with IPT [16] whereas IPT plus iron was the most effective in increasing hemoglobin concentrations There were no significant statistical interactions between HbASAA phenotypes and treatment group However there was a nonsignificant increase in the incidence rate ratio of clinical malaria in the HbAS group not receiv-ing IPT during the 12 weeks of follow-up (IRR = 416 95 CI 05 to 346) and increased geometric mean parasite density in both groups but by far the biggest difference was seen in the group receiving IPT (6203 vs 1853 p = 08 for the interaction) The authors acknowledge that the number of clinical events was very small and that these findings would need veri-fication in a larger study since the number of HbAS individuals (approximately 25 to 30) in each treatment group versus approximately 100 HbAA individuals plus the short follow-up time means that the study was grossly underpowered to assess these outcomes If this

effect is real then the age group studied in this trial (2 to 36 months with 78 lt 18 months) should include the most affected although greater effects might be observed in areas of lower transmission and therefore also in a greater age range of children The results of these two trials warrant urgent further trials or retro-spective analysis of prior trials with sufficient power and detail to make firm conclusions on the effects of common polymorphisms on the response to iron sup-plementation which may be expected to vary by age group and transmission intensity

Clinical trials of IPT during infancy (IPTi) have demonstrated a reduction in the prevalence of anemia in young children in malaria-endemic areas [16 18 38 76] and in some trials a reduction in the incidence of clinical malaria [38 76] and morbidity and mortality in the first year of life [38 77] However the effects may vary depending on the timing of dosing choice of drug local levels of resistance and levels of transmission [78 79] On the basis of our analysis above the impact of IPTi plus iron supplementation may be modulated by levels of hemoglobinopathies and therefore suba-nalyses of these studies should be performed according to genotype wherever possible

Interactions of polymorphisms in host iron metabolism and regulatory proteins with malaria

Polymorphisms of haptoglobin a plasma protein that binds free hemoglobin released from lysed red blood cells recirculating the heme portion to the bone marrow through monocyte and macrophage uptake via CD136 have also been associated with malarial outcomes although reports are conflicting Hap-toglobin exists as three common phenotypes Hp1-1 1-2 and 2-2 In case-control studies in India Sudan Ghana and Cameroon the Hp2-2 phenotype has been associated with protection from severe malaria and placental infection [80ndash83] However two studies that have assessed associations with haptoglobin genotypes did not report any associations [84 85] In a cohort study in Gambian children the Hp2-2 genotype was associated with a greater drop in hemoglobin concen-trations across a malarial transmission season [65] The authors proposed that this effect may have been mediated through an increased prevalence of asymp-tomatic infection observed in the Hp2-2 group which contributed to anemia but could provide protection against severe malaria Interestingly similar but smaller drops in hemoglobin concentration were also observed for heterozygotes for G6PD and HbS We are currently analyzing the effects of low-dose iron supplementation during a malarial transmission season in a similar cohort of children

Inducible heme oxygenase (iHO-1) catalyzes the

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S536 A M Prentice et al

breakdown of heme to generate iron carbon monoxide and biliverdin and is expressed in monocytes and mac-rophages among other cells Biliverdin is subsequently degraded to bilirubin which has potent antioxidant effects Microsatellite polymorphisms in the number of tandem repeats in the promoter of iHO-1 have been variously associated with increased and decreased oxidant stress in various disease pathologies However in a case-control study of cerebral malaria patients in Myanmar homozygotes for the short number of repeats (lt 28) previously associated with higher levels of transcription of iHO-1 were significantly more likely to have cerebral malaria than uncomplicated malaria (odds ratio 314 p = 008) [86] It is not clear how this effect may be mediated but it is possible that it results from increased levels of free iron and resulting oxidant stress

In summary the mechanisms by which various genetic polymorphisms interact with malarial infec-tion are still not clear Furthermore it is not clear how they may affect a possible relationship between iron and malaria especially in relation to supplementation which should be differentiated from that of iron status The current evidence suggests that the heterozygous states of the hemoglobinopathies do not protect against malaria by a simple mechanism involving iron with-holding from the pathogen However the effects of iron supplementation in individuals with the most common polymorphisms should be carefully evaluated taking into account differences in transmission intensity and iron status at baseline

Conclusions

The evidence reviewed above tends to substantiate the concerns raised by the recent Pemba trial that universal administration of iron to children in malarious areas may be associated with adverse outcomes The mecha-nism by which this occurs is far from clear and merits

further research to test whether other chemical forms of supplementary iron might carry less risk There is also evidence that the risk profile will be altered by host genetic variations in hemoglobinopathies G6PD and genes regulating iron metabolism However these insights are not of great practical value because population screening and targeted supplementation programs are not feasible in the areas where iron defi-ciency is most prevalent Likewise the evidence that anemic children are probably at low risk for any adverse outcomes associated with iron supplementation implies a need for prescreening that may not be cost-effective or logistically feasible in developing-country settings

The evidence is fairly clear that malaria causes anemia by diverting iron away from bone marrow and erythropoiesis as part of the inflammatory response and hence iron administration alone is not likely to be the most effective means of combating the anemia Other therapeutic paradigms that combat the inflam-mation and adjust the timing of iron administra-tion to children recovering from malaria should be researched

We suggest that further research is still required to confirm the apparent relationships between iron status and malaria and that such studies should also focus on the underlying mechanisms of the putative interaction This might be achieved through the establishment of a multicountry collaboration to standardize protocols both for iron-supplementation interventions and for the assessment of iron and malaria status indicators Standardizing protocols across variations in age groups malaria transmission patterns and genetic distribu-tions of hemoglobinopathies will provide the evidence for a more targeted approach to policies of prevention and treatment of anemia in malaria-endemic regions

Until this evidence is gathered we recommend that iron supplementation in malarious areas must be accompanied by effective systems for ensuring univer-sal rapid access to diagnosis and treatment of malaria or by preventive therapy

References

1 WHO UNICEF Focusing on anaemia Towards an integrated approach for effective anaemia control Joint WHO UNICEF Statement Geneva Joint WHO UNICEF Statement 2004

2 Oppenheimer SJ Iron and its relation to immunity and infectious disease J Nutr 2001131616Sndash33S discussion 33Sndash35S

3 Murray MJ Murray AB Murray NJ Murray MB Diet and cerebral malaria the effect of famine and refeeding Am J Clin Nutr 19783157ndash61

4 Nyakeriga AM Troye-Blomberg M Dorfman JR Alexander ND Back R Kortok M Chemtai AK Marsh K Williams TN Iron deficiency and malaria among children living on the coast of Kenya J Infect Dis 2004 190439ndash47

5 Oppenheimer SJ Macfarlane SB Moody JB Bunari O Hendrickse RG Effect of iron prophylaxis on morbidity due to infectious disease report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 1986 80596ndash602

6 Shipton D Association between haemoglobin level and susceptibility to malaria a study of Gambian children [MSc dissertation] London London School of Hygiene and Tropical Medicine 2004

7 Snow RW Byass P Shenton FC Greenwood BM The relationship between anthropometric measurements and measurements of iron status and susceptibility to malaria in Gambian children Trans R Soc Trop Med Hyg 199185584ndash9

8 Asobayire FS Adou P Davidsson L Cook JD Hurrell

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S537Iron metabolism and malaria

RF Prevalence of iron deficiency with and without concurrent anemia in population groups with high prevalences of malaria and other infections a study in Cote drsquoIvoire Am J Clin Nutr 200174776ndash82

9 Allen SJ OrsquoDonnell A Alexander ND Alpers MP Peto TE Clegg JB Weatherall DJ alpha+-Thalassemia protects children against disease caused by other infec-tions as well as malaria Proc Natl Acad Sci U S A 1997 9414736ndash41

10 Murray MJ Murray AB Murray MB Murray CJ The adverse effect of iron repletion on the course of certain infections Br Med J 197821113ndash5

11 Smith AW Hendrickse RG Harrison C Hayes RJ Greenwood BM The effects on malaria of treatment of iron-deficiency anaemia with oral iron in Gambian children Ann Trop Paediatr 1989917ndash23

12 Oppenheimer SJ Gibson FD Macfarlane SB Moody JB Harrison C Spencer A Bunari O Iron supplementation increases prevalence and effects of malaria report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 198680603ndash12

13 Byles AB Drsquosa A Reduction of reaction due to iron dextran infusion using chloroquine Br Med J 19703625ndash7

14 Berger J Dyck JL Galan P Aplogan A Schneider D Traissac P Hercberg S Effect of daily iron supplementa-tion on iron status cell-mediated immunity and inci-dence of infections in 6ndash36 month old Togolese children Eur J Clin Nutr 20005429ndash35

15 Chippaux JP Schneider D Aplogan A Dyck JL Berger J [Effects of iron supplementation on malaria infection] Bull Soc Pathol Exot 19918454ndash62

16 Desai MR Mei JV Kariuki SK Wannemuehler KA Phil-lips-Howard PA Nahlen BL Kager PA Vulule JM ter Kuile FO Randomized controlled trial of daily iron sup-plementation and intermittent sulfadoxine-pyrimeth-amine for the treatment of mild childhood anemia in western Kenya J Infect Dis 2003187658ndash66

17 Nwanyanwu OC Ziba C Kazembe PN Gamadzi G Gandwe J Redd SC The effect of oral iron therapy during treatment for Plasmodium falciparum malaria with sulphadoxine-pyrimethamine on Malawian chil-dren under 5 years of age Ann Trop Med Parasitol 199690589ndash95

18 Verhoef H West CE Nzyuko SM de Vogel S van der Valk R Wanga MA Kuijsten A Veenemans J Kok FJ Intermittent administration of iron and sulfadoxine-py-rimethamine to control anaemia in Kenyan children a randomised controlled trial Lancet 2002360908ndash14

19 van den Hombergh J Dalderop E Smit Y Does iron therapy benefit children with severe malaria-associated anaemia A clinical trial with 12 weeks supplementation of oral iron in young children from the Turiani Division Tanzania J Trop Pediatr 199642220ndash7

20 Lawless JW Latham MC Stephenson LS Kinoti SN Pertet AM Iron supplementation improves appetite and growth in anemic Kenyan primary school children J Nutr 1994124645ndash54

21 Mebrahtu T Stoltzfus RJ Chwaya HM Jape JK Savioli L Montresor A Albonico M Tielsch JM Low-dose daily iron supplementation for 12 months does not increase the prevalence of malarial infection or den-sity of parasites in young Zanzibari children J Nutr 20041343037ndash41

22 Menendez C Kahigwa E Hirt R Vounatsou P Aponte JJ Font F Acosta CJ Schellenberg DM Galindo CM Kimario J Urassa H Brabin B Smith TA Kitua AY Tanner M Alonso PL Randomised placebo-controlled trial of iron supplementation and malaria chemoproph-ylaxis for prevention of severe anaemia and malaria in Tanzanian infants Lancet 1997350844ndash50

23 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S MrsquoBoge B Greenwood BM The effects of iron supplementation during pregnancy given by traditional birth attendants on the prevalence of anaemia and malaria Trans R Soc Trop Med Hyg 199488590ndash3

24 van Hensbroek MB Morris-Jones S Meisner S Jaffar S Bayo L Dackour R Phillips C Greenwood BM Iron but not folic acid combined with effective antimalarial therapy promotes haematological recovery in African children after acute falciparum malaria Trans R Soc Trop Med Hyg 199589672ndash6

25 Sazawal S Black RE Ramsan M Chwaya HM Stoltzfus RJ Dutta A Dhingra U Kabole I Deb S Othman MK Kabole FM Effects of routine prophylactic supplemen-tation with iron and folic acid on admission to hospital and mortality in preschool children in a high malaria transmission setting community-based randomised placebo-controlled trial Lancet 2006367133ndash43

26 Harvey PW Heywood PF Nesheim MC Galme K Zegans M Habicht JP Stephenson LS Radimer KL Brabin B Forsyth K et al The effect of iron therapy on malarial infection in Papua New Guinean schoolchil-dren Am J Trop Med Hyg 19894012ndash8

27 Andrews NC Iron homeostasis insights from genetics and animal models Nat Rev Genet 20001208ndash17

28 Kristiansen M Graversen JH Jacobsen C Sonne O Hoffman HJ Law SK Moestrup SK Identification of the haemoglobin scavenger receptor Nature 2001409 198ndash201

29 Wickramasinghe SN Abdalla SH Blood and bone marrow changes in malaria Baillieres Best Pract Res Clin Haematol 200013277ndash99

30 Phillips RE Looareesuwan S Warrell DA Lee SH Karbwang J Warrell MJ White NJ Swasdichai C Weatherall DJ The importance of anaemia in cerebral and uncomplicated falciparum malaria role of compli-cations dyserythropoiesis and iron sequestration Q J Med 198658305ndash23

31 Abdalla S Weatherall DJ Wickramasinghe SN Hughes M The anaemia of P falciparum malaria Br J Haematol 198046171ndash83

32 Sen R Bhatnagar BM Singh U Yadav MS Sehgal PK Patterns of erythropoiesis and anaemia in malaria J Commun Dis 199022247ndash53

33 Srichaikul T Wasanasomsithi M Poshyachinda V Panikbutr N Rabieb T Ferrokinetic studies and eryth-ropoiesis in malaria Arch Intern Med 1969124623ndash8

34 Das BS Thurnham DI Das DB Influence of malaria on markers of iron status in children implications for interpreting iron status in malaria-endemic communi-ties Br J Nutr 199778751ndash60

35 Menendez C Quinto LL Kahigwa E Alvarez L Fern-andez R Gimenez N Schellenberg D Aponte JJ Tanner M Alonso PL Effect of malaria on soluble transferrin receptor levels in Tanzanian infants Am J Trop Med Hyg 200165138ndash42

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S538 A M Prentice et al

36 Stoltzfus RJ Chwaya HM Montresor A Albonico M Savioli L Tielsch JM Malaria hookworms and recent fever are related to anemia and iron status indicators in 0- to 5-y old Zanzibari children and these relationships change with age J Nutr 20001301724ndash33

37 Stoltzfus RJ Chwaya HM Albonico M Schulze KJ Savioli L Tielsch JM Serum ferritin erythrocyte pro-toporphyrin and hemoglobin are valid indicators of iron status of school children in a malaria-holoendemic population J Nutr 1997127293ndash8

38 Massaga JJ Kitua AY Lemnge MM Akida JA Malle LN Ronn AM Theander TG Bygbjerg IC Effect of intermittent treatment with amodiaquine on anaemia and malarial fevers in infants in Tanzania a randomised placebo-controlled trial Lancet 20033611853ndash60

39 Verhoef H West CE Kraaijenhagen R Nzyuko SM King R Mbandi MM van Laatum S Hogervorst R Schep C Kok FJ Malarial anemia leads to adequately increased erythropoiesis in asymptomatic Kenyan children Blood 20021003489ndash94

40 Stoltzfus RJ Chway HM Montresor A Tielsch JM Jape JK Albonico M Savioli L Low dose daily iron supplementation improves iron status and appetite but not anemia whereas quarterly anthelminthic treatment improves growth appetite and anemia in Zanzibari preschool children J Nutr 2004134348ndash56

41 Kurtzhals JA Addae MM Akanmori BD Dunyo S Koram KA Appawu MA Nkrumah FK Hviid L Anae-mia caused by asymptomatic Plasmodium falciparum infection in semi-immune African schoolchildren Trans R Soc Trop Med Hyg 199993623ndash7

42 Loyevsky M John C Dickens B Hu V Miller JH Gordeuk VR Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators Mol Biochem Parasitol 199910143ndash59

43 Scholl PF Tripathi AK Sullivan DJ Bioavailable iron and heme metabolism in Plasmodium falciparum Curr Top Microbiol Immunol 2005295293ndash324

44 Darbari D Loyevsky M Gordeuk V Kark JA Castro O Rana S Apprey V Kurantsin-Mills J Fluorescence meas-urements of the labile iron pool of sickle erythrocytes Blood 2003102357ndash64

45 Ginsburg H Iron acquisition by Plasmodium spp Para-sitol Today 199915466

46 Atamna H Ginsburg H Heme degradation in the presence of glutathione A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells J Biol Chem 199527024876ndash83

47 Gabay T Ginsburg H Hemoglobin denaturation and iron release in acidified red blood cell lysatemdasha possible source of iron for intraerythrocytic malaria parasites Exp Parasitol 199377261ndash72

48 Iyer JK Shi L Shankar AH Sullivan DJ Jr Zinc pro-toporphyrin IX binds heme crystals to inhibit the proc-ess of crystallization in Plasmodium falciparum Mol Med 20039175ndash82

49 Cabantchik ZI Moody-Haupt S Gordeuk VR Iron che-lators as anti-infectives malaria as a paradigm FEMS Immunol Med Microbiol 199926289ndash98

50 Hershko C Control of disease by selective iron deple-tion a novel therapeutic strategy utilizing iron chelators Baillieres Clin Haematol 19947965ndash1000

51 Pradines B Tall A Ramiandrasoa F Spiegel A Sokhna C Fusai T Mosnier J Daries W Trape JF Kunesch G Parzy D Rogier C In vitro activity of iron-binding compounds against Senegalese isolates of Plasmodium falciparum J Antimicrob Chemother 2006571093ndash9

52 Meshnick SR Yang YZ Lima V Kuypers F Kam-chonwongpaisan S Yuthavong Y Iron-dependent free radical generation from the antimalarial agent artem-isinin (qinghaosu) Antimicrob Agents Chemother 1993371108ndash14

53 Golenser J Domb A Mordechai-Daniel T Leshem B Luty A Kremsner P Iron chelators correlation between effects on Plasmodium spp and immune functions J Parasitol 200692170ndash7

54 Nyakeriga AM Williams TN Marsh K Wambua S Perlmann H Perlmann P Grandien A Troye-Blomberg M Cytokine mRNA expression and iron status in chil-dren living in a malaria endemic area Scand J Immunol 200561370ndash5

55 Smith HJ Meremikwu M Iron chelating agents for treating malaria Cochrane Database Syst Rev 2003CD001474

56 Weatherall DJ The global problem of genetic disease Ann Hum Biol 200532117ndash22

57 Williams TN Maitland K Bennett S Ganczakowski M Peto TE Newbold CI Bowden DK Weatherall DJ Clegg JB High incidence of malaria in alpha-thalassaemic children Nature 1996383522ndash5

58 Rees DC Williams TN Maitland K Clegg JB Weather-all DJ Alpha thalassaemia is associated with increased soluble transferrin receptor levels Br J Haematol 1998103365ndash9

59 Maitland K Williams TN Bennett S Newbold CI Peto TE Viji J Timothy R Clegg JB Weatherall DJ Bowden DK The interaction between Plasmodium falciparum and P vivax in children on Espiritu Santo island Van-uatu Trans R Soc Trop Med Hyg 199690614ndash20

60 Weatherall DJ Clegg JB Genetic variability in response to infection malaria and after Genes Immun 2002 3331ndash7

61 Parikh S Dorsey G Rosenthal PJ Host polymorphisms and the incidence of malaria in Ugandan children Am J Trop Med Hyg 200471750ndash3

62 Destro Bisol G Genetic resistance to malaria oxidative stress and hemoglobin oxidation Parassitologia 1999 41203ndash4

63 Cappadoro M Giribaldi G OrsquoBrien E Turrini F Mannu F Ulliers D Simula G Luzzatto L Arese P Early phago-cytosis of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes parasitized by Plasmodium falciparum may explain malaria protection in G6PD deficiency Blood 1998922527ndash34

64 Arese P Turrini F Schwarzer E Band 3complement-mediated recognition and removal of normally senes-cent and pathological human erythrocytes Cell Physiol Biochem 200516133ndash46

65 Atkinson SH Rockett K Sirugo G Bejon PA Fulford A OrsquoConnell M A Bailey R Kwiatkowski DP Prentice AM Seasonal Childhood Anaemia in West Africa Is Associated with the Haptoglobin 2-2 Genotype PLoS Med 20063e172

66 Cabrera G Cot M Migot-Nabias F Kremsner PG Deloron P Luty AJ The sickle cell trait is associated

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S539Iron metabolism and malaria

with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens J Infect Dis 20051911631ndash8

67 Williams TN Mwangi TW Roberts DJ Alexander ND Weatherall DJ Wambua S Kortok M Snow RW Marsh K An immune basis for malaria protection by the sickle cell trait PLoS Med 20052e128

68 Ayi K Turrini F Piga A Arese P Enhanced phagocyto-sis of ring-parasitized mutant erythrocytes a common mechanism that may explain protection against falci-parum malaria in sickle trait and beta-thalassemia trait Blood 20041043364ndash71

69 Roberts DJ Harris T Williams T The influence of inherited traits on malaria infection In Bellamy R ed Susceptibility to infectious diseases the importance of host genetics Cambridge Cambridge University Press 2004 139ndash84

70 Williams TN Mwangi TW Wambua S Alexander ND Kortok M Snow RW Marsh K Sickle cell trait and the risk of Plasmodium falciparum malaria and other child-hood diseases J Infect Dis 2005192178ndash86

71 Aidoo M Terlouw DJ Kolczak MS McElroy PD ter Kuile FO Kariuki S Nahlen BL Lal AA Udhayakumar V Protective effects of the sickle cell gene against malaria morbidity and mortality Lancet 20023591311ndash2

72 Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K Nega-tive epistasis between the malaria-protective effects of alpha+-thalassemia and the sickle cell trait Nat Genet 2005371253ndash7

73 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S Ascaso C Smith T MrsquoBoge B Greenwood BM The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS Trans R Soc Trop Med Hyg 199589289ndash92

74 Terlouw DJ Desai MR Wannemuehler KA Kariuki SK Pfeiffer CM Kager PA Shi YP Ter Kuile FO Relation between the response to iron supplementation and sickle cell hemoglobin phenotype in preschool children in western Kenya Am J Clin Nutr 200479466ndash72

75 Duffy PE Fried M Malaria in the pregnant woman Curr Top Microbiol Immunol 2005295169ndash200

76 Schellenberg D Menendez C Kahigwa E Aponte J Vidal J Tanner M Mshinda H Alonso P Intermittent treatment for malaria and anaemia control at time of routine vaccinations in Tanzanian infants a randomised placebo-controlled trial Lancet 20013571471ndash7

77 Schellenberg D Menendez C Aponte JJ Kahigwa E Tanner M Mshinda H Alonso P Intermittent preventive antimalarial treatment for Tanzanian infants follow-up to age 2 years of a randomised placebo-controlled trial Lancet 20053651481ndash3

78 OrsquoMeara WP Breman JG McKenzie FE The promise and potential challenges of intermittent preventive treat-ment for malaria in infants (IPTi) Malar J 2005433

79 White NJ Intermittent presumptive treatment for malaria PLoS Med 20052e3

80 Elagib AA Kider AO Akerstrom B Elbashir MI Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan Trans R Soc Trop Med Hyg 199892309ndash11

81 Minang JT Gyan BA Anchang JK Troye-Blomberg M Perlmann H Achidi EA Haptoglobin phenotypes and malaria infection in pregnant women at delivery in western Cameroon Acta Trop 200490107ndash14

82 Quaye IK Ekuban FA Goka BQ Adabayeri V Kurtzhals JA Gyan B Ankrah NA Hviid L Akanmori BD Hap-toglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria Trans R Soc Trop Med Hyg 200094216ndash9

83 Singh IP Walter H Bhasin MK Bhardwaj V Sudhakar K Genetic markers and malaria Observations in Gujarat India Hum Hered 19863631ndash6

84 Aucan C Walley AJ Greenwood BM Hill AV Hap-toglobin genotypes are not associated with resistance to severe malaria in The Gambia Trans R Soc Trop Med Hyg 200296327ndash8

85 Bienzle U Eggelte TA Adjei LA Dietz E Ehrhardt S Cramer JP Otchwemah RN Mockenhaupt FP Limited influence of haptoglobin genotypes on severe malaria in Ghanaian children Trop Med Int Health 200510668ndash71

86 Takeda M Kikuchi M Ubalee R Na-Bangchang K Ruangweerayut R Shibahara S Imai S Hirayama K Microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with susceptibility to cerebral malaria in Myanmar Jpn J Infect Dis 2005 58268ndash71

87 Shankar AH Nutritional modulation of malaria mor-bidity and mortality J Infect Dis 2000182 Suppl 1 S37ndash53

88 Gera T Sachdev HP Effect of iron supplementation on incidence of infectious illness in children systematic review Bmj 20023251142

Page 9: Iron metabolism and malaria

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S532 A M Prentice et al

deficiency which is impossible to assess in the presence of malaria In the Gambia we recently compared the absorption of stable-isotope-labeled iron in children anemic as a result of iron deficiency and children anemic after acute malaria Both groups were given 30 days of iron supplementation and the malaria group demonstrated significantly better hemoglobin recovery despite initially significantly reduced iron absorption (Doherty et al unpublished results) Utilization of sequestered iron is likely to be a major contributor to erythroblastic iron requirement after acute malaria

Studies of iron supplementation of populations of anemic children in malarious areas have reported either improved hemoglobin response or decreased prevalence of severe anemia [16 22 38 39] Incorpo-ration of antimalarial intervention arms is common Malaria transmission characteristics study design use of antecedent antimalarials differing iron supplemen-tation doses and differing outcome measures as well as different prevalence rates of iron deficiency and hook-worm infection have made the assessment of factors affecting hemoglobin response to iron supplementation difficult In particular the effect of chronic malaria on response to supplementation in high-transmission areas is unclear as the etiology of the anemia and the chronicity of malaria parasitemia are often undefined in study subjects In an area of intense transmission in Tanzania in which more than 80 of children (4 to 71 months old) were parasitemic at baseline and where malaria infection was strongly associated with hemo-globin supplementation improved the iron status and motor and language development of an iron-deficient population but not did not improve hemoglobin [21 36 40] The authors concluded that factors including malarial parasitemia or ineffective erythropoiesis due to inflammatory processes in a population with high levels of infectious morbidity and inflammation might have limited erythropoiesis

An inflammatory-mediated block to iron absorp-tion and utilization is likely to limit the erythropoietic response to supplemental iron after acute malaria how-ever it is unclear whether chronic parasitemia similarly limits the response to supplemental iron The asso-ciation of chronic malaria with anemia [39] stainable bone marrow iron [34] and increased cytokine levels [41] might suggest a probable effect and the eradica-tion of parasites has been associated with hemoglobin improvement without supplemental iron [31]

Iron metabolism by malaria parasites

In this section we consider whether the availability of iron in the host could modulate the efficiency with which malaria parasites can establish an infection and the severity of that infection What evidence is there to support the ldquonutritional immunityrdquo hypothesis that

host iron availability could limit parasite invasion or multiplication andor the clinical sequelae of para-site infection Support for the nutritional immunity hypothesis first stated in the 1970s has generally waned for the majority of pathogens [2] but there may still be a case for obligate intracellular pathogensmdashincluding Plasmodium spp

It may be informative to examine the research of other scientists than those typically involved in the cur-rent debate For example in order for this hypothesis to be truemdashat least in terms of the success of parasite invasion and replicationmdashit is a requirement that P falciparum be dependent on host iron sources for its survival Next is iron deficiency ever likely to be a limiting factor in the supply of iron to the parasite The most recent research suggests that P falciparum does utilize iron from the host but not from the abundant supplies available in erythrocyte hemoglobin the heme portion of which is quickly degraded to nontoxic but non-iron-bioavailable hemozoin or from the plasma via transferrin but from another source possibly an intraerythrocytic labile pool of ferrous iron [42 43] Interestingly measurements of this labile ferrous iron in normal and sickled erythrocytes indicate it to be positively associated with hemoglobin concentrations and negatively associated with plasma ferritin [44] However other researchers have reported evidence to suggest that the degradation of heme to hemozoin is incomplete and that 50 of heme may be degraded via an alternative pathway involving reduced glutathione and releasing bioavailable iron [45 46] As it has been estimated that less than 1 of heme iron would be sufficient to meet parasite iron requirements [47] iron deficiency would never induce iron-limited growth if hemoglobin were the iron source for parasites

Another mechanism by which iron deficiency may limit parasite growth is that proposed recently by Iyer et al [48] who demonstrated the inhibition of hemozoin formation from toxic free heme by the naturally occur-ring zinc protoporphyrin IX (ZPP) at levels likely to be encountered in anemic erythrocytes It is interesting to note that this is thought to be the mechanism by which the quinoline antimalarials act Furthermore Iyer et al demonstrated that quinolines competed for ZPP bind-ing and prevention of hemozoin formation It is pos-sible that via this mechanism moderate anemia could allow the persistence of low levels of parasitemia and therefore affect the development of exposure-related antibody repertoire and clinical immunitymdashwith consequent effects on future malarial incidence and malaria-associated anemia However the evidence for such an effect in human populations is currently limited due to the lack of longitudinal studies assessing ZPP levels and parasite prevalence and density from infancy onwards

Another research area that has been used to support the hypothesis of decreased iron availability is that

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S533Iron metabolism and malaria

of the effects of iron chelators on parasite growth in vitro and in vivo [49 50] Furthermore some antima-larial drugs such as the antibiotic cyclines including doxycycline are also iron chelators However iron chelators may not be acting by depriving the parasite of iron Alternative mechanisms have been suggested for some chelators including the induction of reactive oxygen species from dissociation of iron from heme and hemozoin as suggested for the lipophilic FR160 [51] similar to the suggested mechanism of artemisinin [52] Furthermore differences between the efficacy of chelators in vitro and in vivo have been associated with differences in immune modulation [53] This may suggest that iron status could affect malarial outcomes via direct effects on immune modulation as suggested by Nyakeriga et al [54] The evidence base for the effects of current iron-chelator therapies in reducing the prevalence density or clinical sequelae of malaria is weakmdashas outlined in a recent Cochrane review of clinical trials involving the use of either desferioxamine or the orally available deferiprone [55] in which all of the seven studies included had limitations relat-ing to study size relevance of study populations and more critically methodological and analytical faults However the authors of this review concluded that the results suggested possible benefits of treatment in cerebral malaria with a shorter recovery time from coma and decreased time to parasite clearance The initial justification for using iron-chelator therapy in cerebral malaria was based on the premise of prevent-ing iron-induced damage to brain cells resulting from hemolysis Therefore it is important to note that the possible benefits of iron-chelator therapy may not relate to limitation of iron for parasite growth and may there-fore not provide evidence in support of the nutritional immunity hypothesis

Iron malaria and hemoglobinopathies

How do hemoglobinopathies protect against parasite invasion or multiplication andor clinical sequelae of parasite infection Are these polymorphisms likely to affect the relationship between iron status or supple-mentation and malaria

J B S Haldane is credited with first postulat-ing heterozygote selection as an explanation for the high prevalence of the thalassemias and later other hemoglobinopathies He suggested that the small size reduced hemoglobin concentrations and increased resistance to hypertonic solutions of such cells may result in decreased parasite invasion or growth Although this hypothesis has been widely accepted for some time it has only recently been possible to dem-onstrate that these mutations have been maintained by selection mostly by malaria but possibly also other infectious causes However the extent and mechanisms

of protection are still debated At least in vitro many studies have failed to demonstrate decreased ability of parasites to invade or grow in thalassemic cells or cells containing hemoglobin S (HbS) Instead the mecha-nisms appear to be more complicated and possibly to vary between local conditions

The common polymorphisms involved in hemo-globin synthesis or red cell formation include sickle hemoglobin (HbS) HbC and HbE the α and β-thalassemias and South Asian ovalocytosis The geographic distribution of these varies across tropi-cal areas and can vary extensively even within closely related regions Current estimates of these polymor-phisms are often based on single sites and are likely to be underestimates [56] but a figure of 27 million carriers of the main hemoglobinopathies has been proposed [56] The carrier frequency for HbS is esti-mated at between 5 and 40 in populations across sub-Saharan Africa the Middle East and parts of South Asia HbC is limited to parts of West and North Africa whereas HbE is common in some parts of India and Southeast Asia with carrier rates up to 60 The thalassemias have the broadest geographic distribution and also the widest range of causative mutations and clinical outcomes The carrier frequencies for the more severe range of β-thalassemias is generally lower than for the α-thalassemias which are estimated to reach carrier frequencies of up to 20 in sub-Saharan Africa higher in Middle Eastern and Indian populations and up to 80 in some Pacific populations (reviewed in Williams et al [57] Rees et al [58] and Maitland et al [59])

In β-thalassemias excess α-globin chains precipitate in red cell precursors leading to ineffective erythropoi-esis and resulting in anemia in the context of increased iron absorption and iron accumulation The clinical expression of β-thalassemia varies widely depending on the exact genetic lesions inherited and interactions with other genetic loci including the α and γ globin genes β-Thalassemia trait and β-thalassemia interme-diate are often asymptomatic and may not be diagnosed except for mild anemia In α-thalassemia the excess β-chains form stable homotetramers which do not sig-nificantly affect erythropoiesis but cause an increased rate of hemolysis of mature cells The degree of the deficit of α-globin chains depends on the number of α-globin genes inactivated and unless three α-globin genes are lost the effects are subtle and various so that the condition will go largely undiagnosed It might be supposed that iron supplementation could be more deleterious in populations with a high prevalence of β-thalassemia mutations because of the inability to utilize the iron leading to increased iron availability to pathogens or iron-induced oxidant stress Interest-ingly Oppenheimer [2] reported that the increased susceptibility to malaria associated with parenteral iron in Papua New Guinean children was not apparent in

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S534 A M Prentice et al

single-deletion α-thalassemia compared with normal children

In a prospective casendashcontrol study in Papua New Guinea α-thalassemic α+ndash homozygotes and α+ndash heterozygotes had a greatly decreased risk of severe malaria (incidence rate ratio = 04 and 066) compared with controls [9] Furthermore protection was also observed for hospitalization from other infections possibly suggesting an immune component to the pro-tection [60] although the reduction of severe malaria may reduce infectious sequelae by invasive bacte-rial disease In apparent contrast α-thalassemia has also been associated with an increased prevalence of uncomplicated malaria in Vanuatu particularly in very young children with P vivax [57] It was suggested that increased red cell turnover in these children increased susceptibility to P vivax [58] resulting in cross-species immunity to P falciparum in later life [59] A similar finding was reported for glucose-6-phosphate dehy-drogenase (G6PD) deficiency in a cohort study in Uganda in which many other potential risk factors for malarial infection were controlled for (age water source use of prophylaxis bednet usage and proxim-ity to mosquito breeding sites) Female heterozygotes for G6PD had a significantly increased incidence of uncomplicated malaria (IRR = 13 p = 03) and a trend for increased parasite densities similar trends were seen for hemizygote males This was different from the pattern observed for HbS heterozygotes who had a nonsignificantly decreased incidence of uncomplicated malaria and decreased parasite densities [61]

A mechanism that has been suggested for G6PD defi-ciency and that may also be applicable to sickle (HbAS) and thalassemic cells involves decreased oxidative protection (G6PD) or increased constitutive oxidative stress of these cells (HbAS αβ thalassemias) especially when infected resulting in increased clearance of the cells from non-malaria-specific immune mechanisms essentially the same as the normal removal of old ldquosenescentrdquo red cells by phagocytes [62ndash64] It has been proposed that such a mechanism could prevent parasitemias from reaching critically high densities and therefore protect from severe malaria and also facilitate the development of antibody repertoires in children from the maintenance of low-grade infections in young children [65ndash67] In a slight modification of this hypothesis the increased phagocytic removal of early ring-stage infected cellsmdashcompared with schizonts and trophozoitesmdashhas been demonstrated for G6PD β-thalassemic and HbAS cells in vitro but not for α-thalassemic infected cells [68] The phagocytosis of ring compared with later stages may be advantageous since rings contain less hemozoin the buildup of which in monocytes has been associated with decreased func-tion Additionally the reduction of the later stages of parasite development may reduce the development of severe symptoms such as cerebral malaria from

reduced endothelial adhesion of late-stage infected red blood cells to receptors such as intracellular adhesion molecule-1 (ICAM-1)

The epidemiological evidence for a protective effect of HbAS suggests that the protective effects are great-est for severe disease (reviewed by Roberts et al [69]) In the most comprehensive study to date a detailed prospective cohort in two Kenyan populations it was reported that HbS heterozygotes had a significantly decreased risk of mild clinical malaria as assessed by active surveillance (50 decreased risk 95 confi-dence interval [CI] 26 to 67]) a 75 (95 CI 84 to 61) decreased risk of hospital admission for malaria and a 90 [95 CI 3 to 99] decreased risk of severe malaria (severe malarial anemia cerebral malaria or complicated malaria) [70] There was no effect of HbAS on the risk of asymptomatic infec-tions or of parasite density in asymptomatic infections assessed at four cross-sectional surveys There were significant decreases in parasite densities for all of the other categories of infection Additionally in this study unlike another in western Kenya [71] the protection was specific to malaria and did not extend to other common childhood infections including respiratory infections gastroenteritis and helminth infections

What influence the hemoglobinopathic and other polymorphisms may have on the effect of iron sup-plementation on malarial susceptibility is potentially dependent on the extent and mechanisms of protection from infection in the different genotypesmdashinfluences that are likely to be further complicated by differential effects according to age and malarial exposure and effects of coinheritance [72] The coinheritance of the HbS G6PD deficiency and α-thalassemia deletion alle-les is likely to be prevalent in sub-Saharan populations making the study of such effects in real populations extremely difficult by requiring very large sample sizes and complex statistical modeling

To the authorsrsquo knowledge only two published randomized controlled trials of iron supplementation have assessed the effects by genotypemdashin both cases by HbAS versus HbAA [73 74]

In the first trial involving Traditional Birth Attend-ant-administered routine iron supplementation to multigravid Gambian pregnant women Menendez et al [73] reported that although overall there were significant beneficial effects on hemoglobin and packed cell volume (PCV) and on birthweight these effects were entirely accounted for by women with the HbAA phenotype (N = 402 vs N = 98) whereas iron-supplemented HbAS women had lower HB PCV and birthweight than HbAA women receiving placebo Furthermore even in this relatively small study these interactions were statistically significant (p lt 01 for hematological indices at delivery baseline measurements as a covariate p lt 03 for birthweight maternal height included as a covariate) Overall

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S535Iron metabolism and malaria

there was no reported increase in susceptibility to malaria as assessed by the prevalence of peripheral malaria at late pregnancy and delivery or by placental histology Yet iron-supplemented HbAS women had an increased prevalence of placental malaria (76 [2229]) compared with iron-supplemented HbAA women (53 [83158]) placebo-treated HbAA women (59 [91154]) or placebo-treated HbAS women (58 [1933]) At the time of this study IPT prophylaxis was recommended only for primigravid pregnant women in the Gambia hence the choice of the study population What the effects of iron supplementation might be in either primigravidae or multigravidae receiving IPTmdashwhich is now recommended for all pregnant women in malaria-endemic countriesmdashhas not been assessed The protection afforded by the HbAS genotype is likely to vary according to gravidity and malarial endemic-ity In areas of high transmission the majority of the increased risk is borne by primigravidae whereas in areas of lower and highly defined seasonal transmis-sion the increased risk extends to a greater number of pregnancies [75] The protective effect of HbAS is thought to be greatest in relatively nonimmune young children who have not yet developed acquired immunity by exposure to a variety of clonal variants of P falciparum and therefore have not developed a full antibody repertoire to the variant surface antigens (VSA) expressed on the cell surfaces of parasitized red blood cells

In the second trial the effect of the HbAS phenotype on the response to iron supplementation in children was assessed in a subanalysis of a 2 times 2 randomized controlled trial of iron supplementation and inter-mittent preventive treatment (IPT) for malaria using sulfadoxinendashpyrimethamine in anemic Kenyan chil-dren (hemoglobin 7 to 109 gdL) [74] There was no reported increase in the susceptibility to clinical malaria or the prevalence of parasitemia at monthly screening associated with the iron supplementation alone or with IPT [16] whereas IPT plus iron was the most effective in increasing hemoglobin concentrations There were no significant statistical interactions between HbASAA phenotypes and treatment group However there was a nonsignificant increase in the incidence rate ratio of clinical malaria in the HbAS group not receiv-ing IPT during the 12 weeks of follow-up (IRR = 416 95 CI 05 to 346) and increased geometric mean parasite density in both groups but by far the biggest difference was seen in the group receiving IPT (6203 vs 1853 p = 08 for the interaction) The authors acknowledge that the number of clinical events was very small and that these findings would need veri-fication in a larger study since the number of HbAS individuals (approximately 25 to 30) in each treatment group versus approximately 100 HbAA individuals plus the short follow-up time means that the study was grossly underpowered to assess these outcomes If this

effect is real then the age group studied in this trial (2 to 36 months with 78 lt 18 months) should include the most affected although greater effects might be observed in areas of lower transmission and therefore also in a greater age range of children The results of these two trials warrant urgent further trials or retro-spective analysis of prior trials with sufficient power and detail to make firm conclusions on the effects of common polymorphisms on the response to iron sup-plementation which may be expected to vary by age group and transmission intensity

Clinical trials of IPT during infancy (IPTi) have demonstrated a reduction in the prevalence of anemia in young children in malaria-endemic areas [16 18 38 76] and in some trials a reduction in the incidence of clinical malaria [38 76] and morbidity and mortality in the first year of life [38 77] However the effects may vary depending on the timing of dosing choice of drug local levels of resistance and levels of transmission [78 79] On the basis of our analysis above the impact of IPTi plus iron supplementation may be modulated by levels of hemoglobinopathies and therefore suba-nalyses of these studies should be performed according to genotype wherever possible

Interactions of polymorphisms in host iron metabolism and regulatory proteins with malaria

Polymorphisms of haptoglobin a plasma protein that binds free hemoglobin released from lysed red blood cells recirculating the heme portion to the bone marrow through monocyte and macrophage uptake via CD136 have also been associated with malarial outcomes although reports are conflicting Hap-toglobin exists as three common phenotypes Hp1-1 1-2 and 2-2 In case-control studies in India Sudan Ghana and Cameroon the Hp2-2 phenotype has been associated with protection from severe malaria and placental infection [80ndash83] However two studies that have assessed associations with haptoglobin genotypes did not report any associations [84 85] In a cohort study in Gambian children the Hp2-2 genotype was associated with a greater drop in hemoglobin concen-trations across a malarial transmission season [65] The authors proposed that this effect may have been mediated through an increased prevalence of asymp-tomatic infection observed in the Hp2-2 group which contributed to anemia but could provide protection against severe malaria Interestingly similar but smaller drops in hemoglobin concentration were also observed for heterozygotes for G6PD and HbS We are currently analyzing the effects of low-dose iron supplementation during a malarial transmission season in a similar cohort of children

Inducible heme oxygenase (iHO-1) catalyzes the

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S536 A M Prentice et al

breakdown of heme to generate iron carbon monoxide and biliverdin and is expressed in monocytes and mac-rophages among other cells Biliverdin is subsequently degraded to bilirubin which has potent antioxidant effects Microsatellite polymorphisms in the number of tandem repeats in the promoter of iHO-1 have been variously associated with increased and decreased oxidant stress in various disease pathologies However in a case-control study of cerebral malaria patients in Myanmar homozygotes for the short number of repeats (lt 28) previously associated with higher levels of transcription of iHO-1 were significantly more likely to have cerebral malaria than uncomplicated malaria (odds ratio 314 p = 008) [86] It is not clear how this effect may be mediated but it is possible that it results from increased levels of free iron and resulting oxidant stress

In summary the mechanisms by which various genetic polymorphisms interact with malarial infec-tion are still not clear Furthermore it is not clear how they may affect a possible relationship between iron and malaria especially in relation to supplementation which should be differentiated from that of iron status The current evidence suggests that the heterozygous states of the hemoglobinopathies do not protect against malaria by a simple mechanism involving iron with-holding from the pathogen However the effects of iron supplementation in individuals with the most common polymorphisms should be carefully evaluated taking into account differences in transmission intensity and iron status at baseline

Conclusions

The evidence reviewed above tends to substantiate the concerns raised by the recent Pemba trial that universal administration of iron to children in malarious areas may be associated with adverse outcomes The mecha-nism by which this occurs is far from clear and merits

further research to test whether other chemical forms of supplementary iron might carry less risk There is also evidence that the risk profile will be altered by host genetic variations in hemoglobinopathies G6PD and genes regulating iron metabolism However these insights are not of great practical value because population screening and targeted supplementation programs are not feasible in the areas where iron defi-ciency is most prevalent Likewise the evidence that anemic children are probably at low risk for any adverse outcomes associated with iron supplementation implies a need for prescreening that may not be cost-effective or logistically feasible in developing-country settings

The evidence is fairly clear that malaria causes anemia by diverting iron away from bone marrow and erythropoiesis as part of the inflammatory response and hence iron administration alone is not likely to be the most effective means of combating the anemia Other therapeutic paradigms that combat the inflam-mation and adjust the timing of iron administra-tion to children recovering from malaria should be researched

We suggest that further research is still required to confirm the apparent relationships between iron status and malaria and that such studies should also focus on the underlying mechanisms of the putative interaction This might be achieved through the establishment of a multicountry collaboration to standardize protocols both for iron-supplementation interventions and for the assessment of iron and malaria status indicators Standardizing protocols across variations in age groups malaria transmission patterns and genetic distribu-tions of hemoglobinopathies will provide the evidence for a more targeted approach to policies of prevention and treatment of anemia in malaria-endemic regions

Until this evidence is gathered we recommend that iron supplementation in malarious areas must be accompanied by effective systems for ensuring univer-sal rapid access to diagnosis and treatment of malaria or by preventive therapy

References

1 WHO UNICEF Focusing on anaemia Towards an integrated approach for effective anaemia control Joint WHO UNICEF Statement Geneva Joint WHO UNICEF Statement 2004

2 Oppenheimer SJ Iron and its relation to immunity and infectious disease J Nutr 2001131616Sndash33S discussion 33Sndash35S

3 Murray MJ Murray AB Murray NJ Murray MB Diet and cerebral malaria the effect of famine and refeeding Am J Clin Nutr 19783157ndash61

4 Nyakeriga AM Troye-Blomberg M Dorfman JR Alexander ND Back R Kortok M Chemtai AK Marsh K Williams TN Iron deficiency and malaria among children living on the coast of Kenya J Infect Dis 2004 190439ndash47

5 Oppenheimer SJ Macfarlane SB Moody JB Bunari O Hendrickse RG Effect of iron prophylaxis on morbidity due to infectious disease report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 1986 80596ndash602

6 Shipton D Association between haemoglobin level and susceptibility to malaria a study of Gambian children [MSc dissertation] London London School of Hygiene and Tropical Medicine 2004

7 Snow RW Byass P Shenton FC Greenwood BM The relationship between anthropometric measurements and measurements of iron status and susceptibility to malaria in Gambian children Trans R Soc Trop Med Hyg 199185584ndash9

8 Asobayire FS Adou P Davidsson L Cook JD Hurrell

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S537Iron metabolism and malaria

RF Prevalence of iron deficiency with and without concurrent anemia in population groups with high prevalences of malaria and other infections a study in Cote drsquoIvoire Am J Clin Nutr 200174776ndash82

9 Allen SJ OrsquoDonnell A Alexander ND Alpers MP Peto TE Clegg JB Weatherall DJ alpha+-Thalassemia protects children against disease caused by other infec-tions as well as malaria Proc Natl Acad Sci U S A 1997 9414736ndash41

10 Murray MJ Murray AB Murray MB Murray CJ The adverse effect of iron repletion on the course of certain infections Br Med J 197821113ndash5

11 Smith AW Hendrickse RG Harrison C Hayes RJ Greenwood BM The effects on malaria of treatment of iron-deficiency anaemia with oral iron in Gambian children Ann Trop Paediatr 1989917ndash23

12 Oppenheimer SJ Gibson FD Macfarlane SB Moody JB Harrison C Spencer A Bunari O Iron supplementation increases prevalence and effects of malaria report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 198680603ndash12

13 Byles AB Drsquosa A Reduction of reaction due to iron dextran infusion using chloroquine Br Med J 19703625ndash7

14 Berger J Dyck JL Galan P Aplogan A Schneider D Traissac P Hercberg S Effect of daily iron supplementa-tion on iron status cell-mediated immunity and inci-dence of infections in 6ndash36 month old Togolese children Eur J Clin Nutr 20005429ndash35

15 Chippaux JP Schneider D Aplogan A Dyck JL Berger J [Effects of iron supplementation on malaria infection] Bull Soc Pathol Exot 19918454ndash62

16 Desai MR Mei JV Kariuki SK Wannemuehler KA Phil-lips-Howard PA Nahlen BL Kager PA Vulule JM ter Kuile FO Randomized controlled trial of daily iron sup-plementation and intermittent sulfadoxine-pyrimeth-amine for the treatment of mild childhood anemia in western Kenya J Infect Dis 2003187658ndash66

17 Nwanyanwu OC Ziba C Kazembe PN Gamadzi G Gandwe J Redd SC The effect of oral iron therapy during treatment for Plasmodium falciparum malaria with sulphadoxine-pyrimethamine on Malawian chil-dren under 5 years of age Ann Trop Med Parasitol 199690589ndash95

18 Verhoef H West CE Nzyuko SM de Vogel S van der Valk R Wanga MA Kuijsten A Veenemans J Kok FJ Intermittent administration of iron and sulfadoxine-py-rimethamine to control anaemia in Kenyan children a randomised controlled trial Lancet 2002360908ndash14

19 van den Hombergh J Dalderop E Smit Y Does iron therapy benefit children with severe malaria-associated anaemia A clinical trial with 12 weeks supplementation of oral iron in young children from the Turiani Division Tanzania J Trop Pediatr 199642220ndash7

20 Lawless JW Latham MC Stephenson LS Kinoti SN Pertet AM Iron supplementation improves appetite and growth in anemic Kenyan primary school children J Nutr 1994124645ndash54

21 Mebrahtu T Stoltzfus RJ Chwaya HM Jape JK Savioli L Montresor A Albonico M Tielsch JM Low-dose daily iron supplementation for 12 months does not increase the prevalence of malarial infection or den-sity of parasites in young Zanzibari children J Nutr 20041343037ndash41

22 Menendez C Kahigwa E Hirt R Vounatsou P Aponte JJ Font F Acosta CJ Schellenberg DM Galindo CM Kimario J Urassa H Brabin B Smith TA Kitua AY Tanner M Alonso PL Randomised placebo-controlled trial of iron supplementation and malaria chemoproph-ylaxis for prevention of severe anaemia and malaria in Tanzanian infants Lancet 1997350844ndash50

23 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S MrsquoBoge B Greenwood BM The effects of iron supplementation during pregnancy given by traditional birth attendants on the prevalence of anaemia and malaria Trans R Soc Trop Med Hyg 199488590ndash3

24 van Hensbroek MB Morris-Jones S Meisner S Jaffar S Bayo L Dackour R Phillips C Greenwood BM Iron but not folic acid combined with effective antimalarial therapy promotes haematological recovery in African children after acute falciparum malaria Trans R Soc Trop Med Hyg 199589672ndash6

25 Sazawal S Black RE Ramsan M Chwaya HM Stoltzfus RJ Dutta A Dhingra U Kabole I Deb S Othman MK Kabole FM Effects of routine prophylactic supplemen-tation with iron and folic acid on admission to hospital and mortality in preschool children in a high malaria transmission setting community-based randomised placebo-controlled trial Lancet 2006367133ndash43

26 Harvey PW Heywood PF Nesheim MC Galme K Zegans M Habicht JP Stephenson LS Radimer KL Brabin B Forsyth K et al The effect of iron therapy on malarial infection in Papua New Guinean schoolchil-dren Am J Trop Med Hyg 19894012ndash8

27 Andrews NC Iron homeostasis insights from genetics and animal models Nat Rev Genet 20001208ndash17

28 Kristiansen M Graversen JH Jacobsen C Sonne O Hoffman HJ Law SK Moestrup SK Identification of the haemoglobin scavenger receptor Nature 2001409 198ndash201

29 Wickramasinghe SN Abdalla SH Blood and bone marrow changes in malaria Baillieres Best Pract Res Clin Haematol 200013277ndash99

30 Phillips RE Looareesuwan S Warrell DA Lee SH Karbwang J Warrell MJ White NJ Swasdichai C Weatherall DJ The importance of anaemia in cerebral and uncomplicated falciparum malaria role of compli-cations dyserythropoiesis and iron sequestration Q J Med 198658305ndash23

31 Abdalla S Weatherall DJ Wickramasinghe SN Hughes M The anaemia of P falciparum malaria Br J Haematol 198046171ndash83

32 Sen R Bhatnagar BM Singh U Yadav MS Sehgal PK Patterns of erythropoiesis and anaemia in malaria J Commun Dis 199022247ndash53

33 Srichaikul T Wasanasomsithi M Poshyachinda V Panikbutr N Rabieb T Ferrokinetic studies and eryth-ropoiesis in malaria Arch Intern Med 1969124623ndash8

34 Das BS Thurnham DI Das DB Influence of malaria on markers of iron status in children implications for interpreting iron status in malaria-endemic communi-ties Br J Nutr 199778751ndash60

35 Menendez C Quinto LL Kahigwa E Alvarez L Fern-andez R Gimenez N Schellenberg D Aponte JJ Tanner M Alonso PL Effect of malaria on soluble transferrin receptor levels in Tanzanian infants Am J Trop Med Hyg 200165138ndash42

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S538 A M Prentice et al

36 Stoltzfus RJ Chwaya HM Montresor A Albonico M Savioli L Tielsch JM Malaria hookworms and recent fever are related to anemia and iron status indicators in 0- to 5-y old Zanzibari children and these relationships change with age J Nutr 20001301724ndash33

37 Stoltzfus RJ Chwaya HM Albonico M Schulze KJ Savioli L Tielsch JM Serum ferritin erythrocyte pro-toporphyrin and hemoglobin are valid indicators of iron status of school children in a malaria-holoendemic population J Nutr 1997127293ndash8

38 Massaga JJ Kitua AY Lemnge MM Akida JA Malle LN Ronn AM Theander TG Bygbjerg IC Effect of intermittent treatment with amodiaquine on anaemia and malarial fevers in infants in Tanzania a randomised placebo-controlled trial Lancet 20033611853ndash60

39 Verhoef H West CE Kraaijenhagen R Nzyuko SM King R Mbandi MM van Laatum S Hogervorst R Schep C Kok FJ Malarial anemia leads to adequately increased erythropoiesis in asymptomatic Kenyan children Blood 20021003489ndash94

40 Stoltzfus RJ Chway HM Montresor A Tielsch JM Jape JK Albonico M Savioli L Low dose daily iron supplementation improves iron status and appetite but not anemia whereas quarterly anthelminthic treatment improves growth appetite and anemia in Zanzibari preschool children J Nutr 2004134348ndash56

41 Kurtzhals JA Addae MM Akanmori BD Dunyo S Koram KA Appawu MA Nkrumah FK Hviid L Anae-mia caused by asymptomatic Plasmodium falciparum infection in semi-immune African schoolchildren Trans R Soc Trop Med Hyg 199993623ndash7

42 Loyevsky M John C Dickens B Hu V Miller JH Gordeuk VR Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators Mol Biochem Parasitol 199910143ndash59

43 Scholl PF Tripathi AK Sullivan DJ Bioavailable iron and heme metabolism in Plasmodium falciparum Curr Top Microbiol Immunol 2005295293ndash324

44 Darbari D Loyevsky M Gordeuk V Kark JA Castro O Rana S Apprey V Kurantsin-Mills J Fluorescence meas-urements of the labile iron pool of sickle erythrocytes Blood 2003102357ndash64

45 Ginsburg H Iron acquisition by Plasmodium spp Para-sitol Today 199915466

46 Atamna H Ginsburg H Heme degradation in the presence of glutathione A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells J Biol Chem 199527024876ndash83

47 Gabay T Ginsburg H Hemoglobin denaturation and iron release in acidified red blood cell lysatemdasha possible source of iron for intraerythrocytic malaria parasites Exp Parasitol 199377261ndash72

48 Iyer JK Shi L Shankar AH Sullivan DJ Jr Zinc pro-toporphyrin IX binds heme crystals to inhibit the proc-ess of crystallization in Plasmodium falciparum Mol Med 20039175ndash82

49 Cabantchik ZI Moody-Haupt S Gordeuk VR Iron che-lators as anti-infectives malaria as a paradigm FEMS Immunol Med Microbiol 199926289ndash98

50 Hershko C Control of disease by selective iron deple-tion a novel therapeutic strategy utilizing iron chelators Baillieres Clin Haematol 19947965ndash1000

51 Pradines B Tall A Ramiandrasoa F Spiegel A Sokhna C Fusai T Mosnier J Daries W Trape JF Kunesch G Parzy D Rogier C In vitro activity of iron-binding compounds against Senegalese isolates of Plasmodium falciparum J Antimicrob Chemother 2006571093ndash9

52 Meshnick SR Yang YZ Lima V Kuypers F Kam-chonwongpaisan S Yuthavong Y Iron-dependent free radical generation from the antimalarial agent artem-isinin (qinghaosu) Antimicrob Agents Chemother 1993371108ndash14

53 Golenser J Domb A Mordechai-Daniel T Leshem B Luty A Kremsner P Iron chelators correlation between effects on Plasmodium spp and immune functions J Parasitol 200692170ndash7

54 Nyakeriga AM Williams TN Marsh K Wambua S Perlmann H Perlmann P Grandien A Troye-Blomberg M Cytokine mRNA expression and iron status in chil-dren living in a malaria endemic area Scand J Immunol 200561370ndash5

55 Smith HJ Meremikwu M Iron chelating agents for treating malaria Cochrane Database Syst Rev 2003CD001474

56 Weatherall DJ The global problem of genetic disease Ann Hum Biol 200532117ndash22

57 Williams TN Maitland K Bennett S Ganczakowski M Peto TE Newbold CI Bowden DK Weatherall DJ Clegg JB High incidence of malaria in alpha-thalassaemic children Nature 1996383522ndash5

58 Rees DC Williams TN Maitland K Clegg JB Weather-all DJ Alpha thalassaemia is associated with increased soluble transferrin receptor levels Br J Haematol 1998103365ndash9

59 Maitland K Williams TN Bennett S Newbold CI Peto TE Viji J Timothy R Clegg JB Weatherall DJ Bowden DK The interaction between Plasmodium falciparum and P vivax in children on Espiritu Santo island Van-uatu Trans R Soc Trop Med Hyg 199690614ndash20

60 Weatherall DJ Clegg JB Genetic variability in response to infection malaria and after Genes Immun 2002 3331ndash7

61 Parikh S Dorsey G Rosenthal PJ Host polymorphisms and the incidence of malaria in Ugandan children Am J Trop Med Hyg 200471750ndash3

62 Destro Bisol G Genetic resistance to malaria oxidative stress and hemoglobin oxidation Parassitologia 1999 41203ndash4

63 Cappadoro M Giribaldi G OrsquoBrien E Turrini F Mannu F Ulliers D Simula G Luzzatto L Arese P Early phago-cytosis of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes parasitized by Plasmodium falciparum may explain malaria protection in G6PD deficiency Blood 1998922527ndash34

64 Arese P Turrini F Schwarzer E Band 3complement-mediated recognition and removal of normally senes-cent and pathological human erythrocytes Cell Physiol Biochem 200516133ndash46

65 Atkinson SH Rockett K Sirugo G Bejon PA Fulford A OrsquoConnell M A Bailey R Kwiatkowski DP Prentice AM Seasonal Childhood Anaemia in West Africa Is Associated with the Haptoglobin 2-2 Genotype PLoS Med 20063e172

66 Cabrera G Cot M Migot-Nabias F Kremsner PG Deloron P Luty AJ The sickle cell trait is associated

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S539Iron metabolism and malaria

with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens J Infect Dis 20051911631ndash8

67 Williams TN Mwangi TW Roberts DJ Alexander ND Weatherall DJ Wambua S Kortok M Snow RW Marsh K An immune basis for malaria protection by the sickle cell trait PLoS Med 20052e128

68 Ayi K Turrini F Piga A Arese P Enhanced phagocyto-sis of ring-parasitized mutant erythrocytes a common mechanism that may explain protection against falci-parum malaria in sickle trait and beta-thalassemia trait Blood 20041043364ndash71

69 Roberts DJ Harris T Williams T The influence of inherited traits on malaria infection In Bellamy R ed Susceptibility to infectious diseases the importance of host genetics Cambridge Cambridge University Press 2004 139ndash84

70 Williams TN Mwangi TW Wambua S Alexander ND Kortok M Snow RW Marsh K Sickle cell trait and the risk of Plasmodium falciparum malaria and other child-hood diseases J Infect Dis 2005192178ndash86

71 Aidoo M Terlouw DJ Kolczak MS McElroy PD ter Kuile FO Kariuki S Nahlen BL Lal AA Udhayakumar V Protective effects of the sickle cell gene against malaria morbidity and mortality Lancet 20023591311ndash2

72 Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K Nega-tive epistasis between the malaria-protective effects of alpha+-thalassemia and the sickle cell trait Nat Genet 2005371253ndash7

73 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S Ascaso C Smith T MrsquoBoge B Greenwood BM The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS Trans R Soc Trop Med Hyg 199589289ndash92

74 Terlouw DJ Desai MR Wannemuehler KA Kariuki SK Pfeiffer CM Kager PA Shi YP Ter Kuile FO Relation between the response to iron supplementation and sickle cell hemoglobin phenotype in preschool children in western Kenya Am J Clin Nutr 200479466ndash72

75 Duffy PE Fried M Malaria in the pregnant woman Curr Top Microbiol Immunol 2005295169ndash200

76 Schellenberg D Menendez C Kahigwa E Aponte J Vidal J Tanner M Mshinda H Alonso P Intermittent treatment for malaria and anaemia control at time of routine vaccinations in Tanzanian infants a randomised placebo-controlled trial Lancet 20013571471ndash7

77 Schellenberg D Menendez C Aponte JJ Kahigwa E Tanner M Mshinda H Alonso P Intermittent preventive antimalarial treatment for Tanzanian infants follow-up to age 2 years of a randomised placebo-controlled trial Lancet 20053651481ndash3

78 OrsquoMeara WP Breman JG McKenzie FE The promise and potential challenges of intermittent preventive treat-ment for malaria in infants (IPTi) Malar J 2005433

79 White NJ Intermittent presumptive treatment for malaria PLoS Med 20052e3

80 Elagib AA Kider AO Akerstrom B Elbashir MI Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan Trans R Soc Trop Med Hyg 199892309ndash11

81 Minang JT Gyan BA Anchang JK Troye-Blomberg M Perlmann H Achidi EA Haptoglobin phenotypes and malaria infection in pregnant women at delivery in western Cameroon Acta Trop 200490107ndash14

82 Quaye IK Ekuban FA Goka BQ Adabayeri V Kurtzhals JA Gyan B Ankrah NA Hviid L Akanmori BD Hap-toglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria Trans R Soc Trop Med Hyg 200094216ndash9

83 Singh IP Walter H Bhasin MK Bhardwaj V Sudhakar K Genetic markers and malaria Observations in Gujarat India Hum Hered 19863631ndash6

84 Aucan C Walley AJ Greenwood BM Hill AV Hap-toglobin genotypes are not associated with resistance to severe malaria in The Gambia Trans R Soc Trop Med Hyg 200296327ndash8

85 Bienzle U Eggelte TA Adjei LA Dietz E Ehrhardt S Cramer JP Otchwemah RN Mockenhaupt FP Limited influence of haptoglobin genotypes on severe malaria in Ghanaian children Trop Med Int Health 200510668ndash71

86 Takeda M Kikuchi M Ubalee R Na-Bangchang K Ruangweerayut R Shibahara S Imai S Hirayama K Microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with susceptibility to cerebral malaria in Myanmar Jpn J Infect Dis 2005 58268ndash71

87 Shankar AH Nutritional modulation of malaria mor-bidity and mortality J Infect Dis 2000182 Suppl 1 S37ndash53

88 Gera T Sachdev HP Effect of iron supplementation on incidence of infectious illness in children systematic review Bmj 20023251142

Page 10: Iron metabolism and malaria

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S533Iron metabolism and malaria

of the effects of iron chelators on parasite growth in vitro and in vivo [49 50] Furthermore some antima-larial drugs such as the antibiotic cyclines including doxycycline are also iron chelators However iron chelators may not be acting by depriving the parasite of iron Alternative mechanisms have been suggested for some chelators including the induction of reactive oxygen species from dissociation of iron from heme and hemozoin as suggested for the lipophilic FR160 [51] similar to the suggested mechanism of artemisinin [52] Furthermore differences between the efficacy of chelators in vitro and in vivo have been associated with differences in immune modulation [53] This may suggest that iron status could affect malarial outcomes via direct effects on immune modulation as suggested by Nyakeriga et al [54] The evidence base for the effects of current iron-chelator therapies in reducing the prevalence density or clinical sequelae of malaria is weakmdashas outlined in a recent Cochrane review of clinical trials involving the use of either desferioxamine or the orally available deferiprone [55] in which all of the seven studies included had limitations relat-ing to study size relevance of study populations and more critically methodological and analytical faults However the authors of this review concluded that the results suggested possible benefits of treatment in cerebral malaria with a shorter recovery time from coma and decreased time to parasite clearance The initial justification for using iron-chelator therapy in cerebral malaria was based on the premise of prevent-ing iron-induced damage to brain cells resulting from hemolysis Therefore it is important to note that the possible benefits of iron-chelator therapy may not relate to limitation of iron for parasite growth and may there-fore not provide evidence in support of the nutritional immunity hypothesis

Iron malaria and hemoglobinopathies

How do hemoglobinopathies protect against parasite invasion or multiplication andor clinical sequelae of parasite infection Are these polymorphisms likely to affect the relationship between iron status or supple-mentation and malaria

J B S Haldane is credited with first postulat-ing heterozygote selection as an explanation for the high prevalence of the thalassemias and later other hemoglobinopathies He suggested that the small size reduced hemoglobin concentrations and increased resistance to hypertonic solutions of such cells may result in decreased parasite invasion or growth Although this hypothesis has been widely accepted for some time it has only recently been possible to dem-onstrate that these mutations have been maintained by selection mostly by malaria but possibly also other infectious causes However the extent and mechanisms

of protection are still debated At least in vitro many studies have failed to demonstrate decreased ability of parasites to invade or grow in thalassemic cells or cells containing hemoglobin S (HbS) Instead the mecha-nisms appear to be more complicated and possibly to vary between local conditions

The common polymorphisms involved in hemo-globin synthesis or red cell formation include sickle hemoglobin (HbS) HbC and HbE the α and β-thalassemias and South Asian ovalocytosis The geographic distribution of these varies across tropi-cal areas and can vary extensively even within closely related regions Current estimates of these polymor-phisms are often based on single sites and are likely to be underestimates [56] but a figure of 27 million carriers of the main hemoglobinopathies has been proposed [56] The carrier frequency for HbS is esti-mated at between 5 and 40 in populations across sub-Saharan Africa the Middle East and parts of South Asia HbC is limited to parts of West and North Africa whereas HbE is common in some parts of India and Southeast Asia with carrier rates up to 60 The thalassemias have the broadest geographic distribution and also the widest range of causative mutations and clinical outcomes The carrier frequencies for the more severe range of β-thalassemias is generally lower than for the α-thalassemias which are estimated to reach carrier frequencies of up to 20 in sub-Saharan Africa higher in Middle Eastern and Indian populations and up to 80 in some Pacific populations (reviewed in Williams et al [57] Rees et al [58] and Maitland et al [59])

In β-thalassemias excess α-globin chains precipitate in red cell precursors leading to ineffective erythropoi-esis and resulting in anemia in the context of increased iron absorption and iron accumulation The clinical expression of β-thalassemia varies widely depending on the exact genetic lesions inherited and interactions with other genetic loci including the α and γ globin genes β-Thalassemia trait and β-thalassemia interme-diate are often asymptomatic and may not be diagnosed except for mild anemia In α-thalassemia the excess β-chains form stable homotetramers which do not sig-nificantly affect erythropoiesis but cause an increased rate of hemolysis of mature cells The degree of the deficit of α-globin chains depends on the number of α-globin genes inactivated and unless three α-globin genes are lost the effects are subtle and various so that the condition will go largely undiagnosed It might be supposed that iron supplementation could be more deleterious in populations with a high prevalence of β-thalassemia mutations because of the inability to utilize the iron leading to increased iron availability to pathogens or iron-induced oxidant stress Interest-ingly Oppenheimer [2] reported that the increased susceptibility to malaria associated with parenteral iron in Papua New Guinean children was not apparent in

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S534 A M Prentice et al

single-deletion α-thalassemia compared with normal children

In a prospective casendashcontrol study in Papua New Guinea α-thalassemic α+ndash homozygotes and α+ndash heterozygotes had a greatly decreased risk of severe malaria (incidence rate ratio = 04 and 066) compared with controls [9] Furthermore protection was also observed for hospitalization from other infections possibly suggesting an immune component to the pro-tection [60] although the reduction of severe malaria may reduce infectious sequelae by invasive bacte-rial disease In apparent contrast α-thalassemia has also been associated with an increased prevalence of uncomplicated malaria in Vanuatu particularly in very young children with P vivax [57] It was suggested that increased red cell turnover in these children increased susceptibility to P vivax [58] resulting in cross-species immunity to P falciparum in later life [59] A similar finding was reported for glucose-6-phosphate dehy-drogenase (G6PD) deficiency in a cohort study in Uganda in which many other potential risk factors for malarial infection were controlled for (age water source use of prophylaxis bednet usage and proxim-ity to mosquito breeding sites) Female heterozygotes for G6PD had a significantly increased incidence of uncomplicated malaria (IRR = 13 p = 03) and a trend for increased parasite densities similar trends were seen for hemizygote males This was different from the pattern observed for HbS heterozygotes who had a nonsignificantly decreased incidence of uncomplicated malaria and decreased parasite densities [61]

A mechanism that has been suggested for G6PD defi-ciency and that may also be applicable to sickle (HbAS) and thalassemic cells involves decreased oxidative protection (G6PD) or increased constitutive oxidative stress of these cells (HbAS αβ thalassemias) especially when infected resulting in increased clearance of the cells from non-malaria-specific immune mechanisms essentially the same as the normal removal of old ldquosenescentrdquo red cells by phagocytes [62ndash64] It has been proposed that such a mechanism could prevent parasitemias from reaching critically high densities and therefore protect from severe malaria and also facilitate the development of antibody repertoires in children from the maintenance of low-grade infections in young children [65ndash67] In a slight modification of this hypothesis the increased phagocytic removal of early ring-stage infected cellsmdashcompared with schizonts and trophozoitesmdashhas been demonstrated for G6PD β-thalassemic and HbAS cells in vitro but not for α-thalassemic infected cells [68] The phagocytosis of ring compared with later stages may be advantageous since rings contain less hemozoin the buildup of which in monocytes has been associated with decreased func-tion Additionally the reduction of the later stages of parasite development may reduce the development of severe symptoms such as cerebral malaria from

reduced endothelial adhesion of late-stage infected red blood cells to receptors such as intracellular adhesion molecule-1 (ICAM-1)

The epidemiological evidence for a protective effect of HbAS suggests that the protective effects are great-est for severe disease (reviewed by Roberts et al [69]) In the most comprehensive study to date a detailed prospective cohort in two Kenyan populations it was reported that HbS heterozygotes had a significantly decreased risk of mild clinical malaria as assessed by active surveillance (50 decreased risk 95 confi-dence interval [CI] 26 to 67]) a 75 (95 CI 84 to 61) decreased risk of hospital admission for malaria and a 90 [95 CI 3 to 99] decreased risk of severe malaria (severe malarial anemia cerebral malaria or complicated malaria) [70] There was no effect of HbAS on the risk of asymptomatic infec-tions or of parasite density in asymptomatic infections assessed at four cross-sectional surveys There were significant decreases in parasite densities for all of the other categories of infection Additionally in this study unlike another in western Kenya [71] the protection was specific to malaria and did not extend to other common childhood infections including respiratory infections gastroenteritis and helminth infections

What influence the hemoglobinopathic and other polymorphisms may have on the effect of iron sup-plementation on malarial susceptibility is potentially dependent on the extent and mechanisms of protection from infection in the different genotypesmdashinfluences that are likely to be further complicated by differential effects according to age and malarial exposure and effects of coinheritance [72] The coinheritance of the HbS G6PD deficiency and α-thalassemia deletion alle-les is likely to be prevalent in sub-Saharan populations making the study of such effects in real populations extremely difficult by requiring very large sample sizes and complex statistical modeling

To the authorsrsquo knowledge only two published randomized controlled trials of iron supplementation have assessed the effects by genotypemdashin both cases by HbAS versus HbAA [73 74]

In the first trial involving Traditional Birth Attend-ant-administered routine iron supplementation to multigravid Gambian pregnant women Menendez et al [73] reported that although overall there were significant beneficial effects on hemoglobin and packed cell volume (PCV) and on birthweight these effects were entirely accounted for by women with the HbAA phenotype (N = 402 vs N = 98) whereas iron-supplemented HbAS women had lower HB PCV and birthweight than HbAA women receiving placebo Furthermore even in this relatively small study these interactions were statistically significant (p lt 01 for hematological indices at delivery baseline measurements as a covariate p lt 03 for birthweight maternal height included as a covariate) Overall

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S535Iron metabolism and malaria

there was no reported increase in susceptibility to malaria as assessed by the prevalence of peripheral malaria at late pregnancy and delivery or by placental histology Yet iron-supplemented HbAS women had an increased prevalence of placental malaria (76 [2229]) compared with iron-supplemented HbAA women (53 [83158]) placebo-treated HbAA women (59 [91154]) or placebo-treated HbAS women (58 [1933]) At the time of this study IPT prophylaxis was recommended only for primigravid pregnant women in the Gambia hence the choice of the study population What the effects of iron supplementation might be in either primigravidae or multigravidae receiving IPTmdashwhich is now recommended for all pregnant women in malaria-endemic countriesmdashhas not been assessed The protection afforded by the HbAS genotype is likely to vary according to gravidity and malarial endemic-ity In areas of high transmission the majority of the increased risk is borne by primigravidae whereas in areas of lower and highly defined seasonal transmis-sion the increased risk extends to a greater number of pregnancies [75] The protective effect of HbAS is thought to be greatest in relatively nonimmune young children who have not yet developed acquired immunity by exposure to a variety of clonal variants of P falciparum and therefore have not developed a full antibody repertoire to the variant surface antigens (VSA) expressed on the cell surfaces of parasitized red blood cells

In the second trial the effect of the HbAS phenotype on the response to iron supplementation in children was assessed in a subanalysis of a 2 times 2 randomized controlled trial of iron supplementation and inter-mittent preventive treatment (IPT) for malaria using sulfadoxinendashpyrimethamine in anemic Kenyan chil-dren (hemoglobin 7 to 109 gdL) [74] There was no reported increase in the susceptibility to clinical malaria or the prevalence of parasitemia at monthly screening associated with the iron supplementation alone or with IPT [16] whereas IPT plus iron was the most effective in increasing hemoglobin concentrations There were no significant statistical interactions between HbASAA phenotypes and treatment group However there was a nonsignificant increase in the incidence rate ratio of clinical malaria in the HbAS group not receiv-ing IPT during the 12 weeks of follow-up (IRR = 416 95 CI 05 to 346) and increased geometric mean parasite density in both groups but by far the biggest difference was seen in the group receiving IPT (6203 vs 1853 p = 08 for the interaction) The authors acknowledge that the number of clinical events was very small and that these findings would need veri-fication in a larger study since the number of HbAS individuals (approximately 25 to 30) in each treatment group versus approximately 100 HbAA individuals plus the short follow-up time means that the study was grossly underpowered to assess these outcomes If this

effect is real then the age group studied in this trial (2 to 36 months with 78 lt 18 months) should include the most affected although greater effects might be observed in areas of lower transmission and therefore also in a greater age range of children The results of these two trials warrant urgent further trials or retro-spective analysis of prior trials with sufficient power and detail to make firm conclusions on the effects of common polymorphisms on the response to iron sup-plementation which may be expected to vary by age group and transmission intensity

Clinical trials of IPT during infancy (IPTi) have demonstrated a reduction in the prevalence of anemia in young children in malaria-endemic areas [16 18 38 76] and in some trials a reduction in the incidence of clinical malaria [38 76] and morbidity and mortality in the first year of life [38 77] However the effects may vary depending on the timing of dosing choice of drug local levels of resistance and levels of transmission [78 79] On the basis of our analysis above the impact of IPTi plus iron supplementation may be modulated by levels of hemoglobinopathies and therefore suba-nalyses of these studies should be performed according to genotype wherever possible

Interactions of polymorphisms in host iron metabolism and regulatory proteins with malaria

Polymorphisms of haptoglobin a plasma protein that binds free hemoglobin released from lysed red blood cells recirculating the heme portion to the bone marrow through monocyte and macrophage uptake via CD136 have also been associated with malarial outcomes although reports are conflicting Hap-toglobin exists as three common phenotypes Hp1-1 1-2 and 2-2 In case-control studies in India Sudan Ghana and Cameroon the Hp2-2 phenotype has been associated with protection from severe malaria and placental infection [80ndash83] However two studies that have assessed associations with haptoglobin genotypes did not report any associations [84 85] In a cohort study in Gambian children the Hp2-2 genotype was associated with a greater drop in hemoglobin concen-trations across a malarial transmission season [65] The authors proposed that this effect may have been mediated through an increased prevalence of asymp-tomatic infection observed in the Hp2-2 group which contributed to anemia but could provide protection against severe malaria Interestingly similar but smaller drops in hemoglobin concentration were also observed for heterozygotes for G6PD and HbS We are currently analyzing the effects of low-dose iron supplementation during a malarial transmission season in a similar cohort of children

Inducible heme oxygenase (iHO-1) catalyzes the

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S536 A M Prentice et al

breakdown of heme to generate iron carbon monoxide and biliverdin and is expressed in monocytes and mac-rophages among other cells Biliverdin is subsequently degraded to bilirubin which has potent antioxidant effects Microsatellite polymorphisms in the number of tandem repeats in the promoter of iHO-1 have been variously associated with increased and decreased oxidant stress in various disease pathologies However in a case-control study of cerebral malaria patients in Myanmar homozygotes for the short number of repeats (lt 28) previously associated with higher levels of transcription of iHO-1 were significantly more likely to have cerebral malaria than uncomplicated malaria (odds ratio 314 p = 008) [86] It is not clear how this effect may be mediated but it is possible that it results from increased levels of free iron and resulting oxidant stress

In summary the mechanisms by which various genetic polymorphisms interact with malarial infec-tion are still not clear Furthermore it is not clear how they may affect a possible relationship between iron and malaria especially in relation to supplementation which should be differentiated from that of iron status The current evidence suggests that the heterozygous states of the hemoglobinopathies do not protect against malaria by a simple mechanism involving iron with-holding from the pathogen However the effects of iron supplementation in individuals with the most common polymorphisms should be carefully evaluated taking into account differences in transmission intensity and iron status at baseline

Conclusions

The evidence reviewed above tends to substantiate the concerns raised by the recent Pemba trial that universal administration of iron to children in malarious areas may be associated with adverse outcomes The mecha-nism by which this occurs is far from clear and merits

further research to test whether other chemical forms of supplementary iron might carry less risk There is also evidence that the risk profile will be altered by host genetic variations in hemoglobinopathies G6PD and genes regulating iron metabolism However these insights are not of great practical value because population screening and targeted supplementation programs are not feasible in the areas where iron defi-ciency is most prevalent Likewise the evidence that anemic children are probably at low risk for any adverse outcomes associated with iron supplementation implies a need for prescreening that may not be cost-effective or logistically feasible in developing-country settings

The evidence is fairly clear that malaria causes anemia by diverting iron away from bone marrow and erythropoiesis as part of the inflammatory response and hence iron administration alone is not likely to be the most effective means of combating the anemia Other therapeutic paradigms that combat the inflam-mation and adjust the timing of iron administra-tion to children recovering from malaria should be researched

We suggest that further research is still required to confirm the apparent relationships between iron status and malaria and that such studies should also focus on the underlying mechanisms of the putative interaction This might be achieved through the establishment of a multicountry collaboration to standardize protocols both for iron-supplementation interventions and for the assessment of iron and malaria status indicators Standardizing protocols across variations in age groups malaria transmission patterns and genetic distribu-tions of hemoglobinopathies will provide the evidence for a more targeted approach to policies of prevention and treatment of anemia in malaria-endemic regions

Until this evidence is gathered we recommend that iron supplementation in malarious areas must be accompanied by effective systems for ensuring univer-sal rapid access to diagnosis and treatment of malaria or by preventive therapy

References

1 WHO UNICEF Focusing on anaemia Towards an integrated approach for effective anaemia control Joint WHO UNICEF Statement Geneva Joint WHO UNICEF Statement 2004

2 Oppenheimer SJ Iron and its relation to immunity and infectious disease J Nutr 2001131616Sndash33S discussion 33Sndash35S

3 Murray MJ Murray AB Murray NJ Murray MB Diet and cerebral malaria the effect of famine and refeeding Am J Clin Nutr 19783157ndash61

4 Nyakeriga AM Troye-Blomberg M Dorfman JR Alexander ND Back R Kortok M Chemtai AK Marsh K Williams TN Iron deficiency and malaria among children living on the coast of Kenya J Infect Dis 2004 190439ndash47

5 Oppenheimer SJ Macfarlane SB Moody JB Bunari O Hendrickse RG Effect of iron prophylaxis on morbidity due to infectious disease report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 1986 80596ndash602

6 Shipton D Association between haemoglobin level and susceptibility to malaria a study of Gambian children [MSc dissertation] London London School of Hygiene and Tropical Medicine 2004

7 Snow RW Byass P Shenton FC Greenwood BM The relationship between anthropometric measurements and measurements of iron status and susceptibility to malaria in Gambian children Trans R Soc Trop Med Hyg 199185584ndash9

8 Asobayire FS Adou P Davidsson L Cook JD Hurrell

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S537Iron metabolism and malaria

RF Prevalence of iron deficiency with and without concurrent anemia in population groups with high prevalences of malaria and other infections a study in Cote drsquoIvoire Am J Clin Nutr 200174776ndash82

9 Allen SJ OrsquoDonnell A Alexander ND Alpers MP Peto TE Clegg JB Weatherall DJ alpha+-Thalassemia protects children against disease caused by other infec-tions as well as malaria Proc Natl Acad Sci U S A 1997 9414736ndash41

10 Murray MJ Murray AB Murray MB Murray CJ The adverse effect of iron repletion on the course of certain infections Br Med J 197821113ndash5

11 Smith AW Hendrickse RG Harrison C Hayes RJ Greenwood BM The effects on malaria of treatment of iron-deficiency anaemia with oral iron in Gambian children Ann Trop Paediatr 1989917ndash23

12 Oppenheimer SJ Gibson FD Macfarlane SB Moody JB Harrison C Spencer A Bunari O Iron supplementation increases prevalence and effects of malaria report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 198680603ndash12

13 Byles AB Drsquosa A Reduction of reaction due to iron dextran infusion using chloroquine Br Med J 19703625ndash7

14 Berger J Dyck JL Galan P Aplogan A Schneider D Traissac P Hercberg S Effect of daily iron supplementa-tion on iron status cell-mediated immunity and inci-dence of infections in 6ndash36 month old Togolese children Eur J Clin Nutr 20005429ndash35

15 Chippaux JP Schneider D Aplogan A Dyck JL Berger J [Effects of iron supplementation on malaria infection] Bull Soc Pathol Exot 19918454ndash62

16 Desai MR Mei JV Kariuki SK Wannemuehler KA Phil-lips-Howard PA Nahlen BL Kager PA Vulule JM ter Kuile FO Randomized controlled trial of daily iron sup-plementation and intermittent sulfadoxine-pyrimeth-amine for the treatment of mild childhood anemia in western Kenya J Infect Dis 2003187658ndash66

17 Nwanyanwu OC Ziba C Kazembe PN Gamadzi G Gandwe J Redd SC The effect of oral iron therapy during treatment for Plasmodium falciparum malaria with sulphadoxine-pyrimethamine on Malawian chil-dren under 5 years of age Ann Trop Med Parasitol 199690589ndash95

18 Verhoef H West CE Nzyuko SM de Vogel S van der Valk R Wanga MA Kuijsten A Veenemans J Kok FJ Intermittent administration of iron and sulfadoxine-py-rimethamine to control anaemia in Kenyan children a randomised controlled trial Lancet 2002360908ndash14

19 van den Hombergh J Dalderop E Smit Y Does iron therapy benefit children with severe malaria-associated anaemia A clinical trial with 12 weeks supplementation of oral iron in young children from the Turiani Division Tanzania J Trop Pediatr 199642220ndash7

20 Lawless JW Latham MC Stephenson LS Kinoti SN Pertet AM Iron supplementation improves appetite and growth in anemic Kenyan primary school children J Nutr 1994124645ndash54

21 Mebrahtu T Stoltzfus RJ Chwaya HM Jape JK Savioli L Montresor A Albonico M Tielsch JM Low-dose daily iron supplementation for 12 months does not increase the prevalence of malarial infection or den-sity of parasites in young Zanzibari children J Nutr 20041343037ndash41

22 Menendez C Kahigwa E Hirt R Vounatsou P Aponte JJ Font F Acosta CJ Schellenberg DM Galindo CM Kimario J Urassa H Brabin B Smith TA Kitua AY Tanner M Alonso PL Randomised placebo-controlled trial of iron supplementation and malaria chemoproph-ylaxis for prevention of severe anaemia and malaria in Tanzanian infants Lancet 1997350844ndash50

23 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S MrsquoBoge B Greenwood BM The effects of iron supplementation during pregnancy given by traditional birth attendants on the prevalence of anaemia and malaria Trans R Soc Trop Med Hyg 199488590ndash3

24 van Hensbroek MB Morris-Jones S Meisner S Jaffar S Bayo L Dackour R Phillips C Greenwood BM Iron but not folic acid combined with effective antimalarial therapy promotes haematological recovery in African children after acute falciparum malaria Trans R Soc Trop Med Hyg 199589672ndash6

25 Sazawal S Black RE Ramsan M Chwaya HM Stoltzfus RJ Dutta A Dhingra U Kabole I Deb S Othman MK Kabole FM Effects of routine prophylactic supplemen-tation with iron and folic acid on admission to hospital and mortality in preschool children in a high malaria transmission setting community-based randomised placebo-controlled trial Lancet 2006367133ndash43

26 Harvey PW Heywood PF Nesheim MC Galme K Zegans M Habicht JP Stephenson LS Radimer KL Brabin B Forsyth K et al The effect of iron therapy on malarial infection in Papua New Guinean schoolchil-dren Am J Trop Med Hyg 19894012ndash8

27 Andrews NC Iron homeostasis insights from genetics and animal models Nat Rev Genet 20001208ndash17

28 Kristiansen M Graversen JH Jacobsen C Sonne O Hoffman HJ Law SK Moestrup SK Identification of the haemoglobin scavenger receptor Nature 2001409 198ndash201

29 Wickramasinghe SN Abdalla SH Blood and bone marrow changes in malaria Baillieres Best Pract Res Clin Haematol 200013277ndash99

30 Phillips RE Looareesuwan S Warrell DA Lee SH Karbwang J Warrell MJ White NJ Swasdichai C Weatherall DJ The importance of anaemia in cerebral and uncomplicated falciparum malaria role of compli-cations dyserythropoiesis and iron sequestration Q J Med 198658305ndash23

31 Abdalla S Weatherall DJ Wickramasinghe SN Hughes M The anaemia of P falciparum malaria Br J Haematol 198046171ndash83

32 Sen R Bhatnagar BM Singh U Yadav MS Sehgal PK Patterns of erythropoiesis and anaemia in malaria J Commun Dis 199022247ndash53

33 Srichaikul T Wasanasomsithi M Poshyachinda V Panikbutr N Rabieb T Ferrokinetic studies and eryth-ropoiesis in malaria Arch Intern Med 1969124623ndash8

34 Das BS Thurnham DI Das DB Influence of malaria on markers of iron status in children implications for interpreting iron status in malaria-endemic communi-ties Br J Nutr 199778751ndash60

35 Menendez C Quinto LL Kahigwa E Alvarez L Fern-andez R Gimenez N Schellenberg D Aponte JJ Tanner M Alonso PL Effect of malaria on soluble transferrin receptor levels in Tanzanian infants Am J Trop Med Hyg 200165138ndash42

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S538 A M Prentice et al

36 Stoltzfus RJ Chwaya HM Montresor A Albonico M Savioli L Tielsch JM Malaria hookworms and recent fever are related to anemia and iron status indicators in 0- to 5-y old Zanzibari children and these relationships change with age J Nutr 20001301724ndash33

37 Stoltzfus RJ Chwaya HM Albonico M Schulze KJ Savioli L Tielsch JM Serum ferritin erythrocyte pro-toporphyrin and hemoglobin are valid indicators of iron status of school children in a malaria-holoendemic population J Nutr 1997127293ndash8

38 Massaga JJ Kitua AY Lemnge MM Akida JA Malle LN Ronn AM Theander TG Bygbjerg IC Effect of intermittent treatment with amodiaquine on anaemia and malarial fevers in infants in Tanzania a randomised placebo-controlled trial Lancet 20033611853ndash60

39 Verhoef H West CE Kraaijenhagen R Nzyuko SM King R Mbandi MM van Laatum S Hogervorst R Schep C Kok FJ Malarial anemia leads to adequately increased erythropoiesis in asymptomatic Kenyan children Blood 20021003489ndash94

40 Stoltzfus RJ Chway HM Montresor A Tielsch JM Jape JK Albonico M Savioli L Low dose daily iron supplementation improves iron status and appetite but not anemia whereas quarterly anthelminthic treatment improves growth appetite and anemia in Zanzibari preschool children J Nutr 2004134348ndash56

41 Kurtzhals JA Addae MM Akanmori BD Dunyo S Koram KA Appawu MA Nkrumah FK Hviid L Anae-mia caused by asymptomatic Plasmodium falciparum infection in semi-immune African schoolchildren Trans R Soc Trop Med Hyg 199993623ndash7

42 Loyevsky M John C Dickens B Hu V Miller JH Gordeuk VR Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators Mol Biochem Parasitol 199910143ndash59

43 Scholl PF Tripathi AK Sullivan DJ Bioavailable iron and heme metabolism in Plasmodium falciparum Curr Top Microbiol Immunol 2005295293ndash324

44 Darbari D Loyevsky M Gordeuk V Kark JA Castro O Rana S Apprey V Kurantsin-Mills J Fluorescence meas-urements of the labile iron pool of sickle erythrocytes Blood 2003102357ndash64

45 Ginsburg H Iron acquisition by Plasmodium spp Para-sitol Today 199915466

46 Atamna H Ginsburg H Heme degradation in the presence of glutathione A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells J Biol Chem 199527024876ndash83

47 Gabay T Ginsburg H Hemoglobin denaturation and iron release in acidified red blood cell lysatemdasha possible source of iron for intraerythrocytic malaria parasites Exp Parasitol 199377261ndash72

48 Iyer JK Shi L Shankar AH Sullivan DJ Jr Zinc pro-toporphyrin IX binds heme crystals to inhibit the proc-ess of crystallization in Plasmodium falciparum Mol Med 20039175ndash82

49 Cabantchik ZI Moody-Haupt S Gordeuk VR Iron che-lators as anti-infectives malaria as a paradigm FEMS Immunol Med Microbiol 199926289ndash98

50 Hershko C Control of disease by selective iron deple-tion a novel therapeutic strategy utilizing iron chelators Baillieres Clin Haematol 19947965ndash1000

51 Pradines B Tall A Ramiandrasoa F Spiegel A Sokhna C Fusai T Mosnier J Daries W Trape JF Kunesch G Parzy D Rogier C In vitro activity of iron-binding compounds against Senegalese isolates of Plasmodium falciparum J Antimicrob Chemother 2006571093ndash9

52 Meshnick SR Yang YZ Lima V Kuypers F Kam-chonwongpaisan S Yuthavong Y Iron-dependent free radical generation from the antimalarial agent artem-isinin (qinghaosu) Antimicrob Agents Chemother 1993371108ndash14

53 Golenser J Domb A Mordechai-Daniel T Leshem B Luty A Kremsner P Iron chelators correlation between effects on Plasmodium spp and immune functions J Parasitol 200692170ndash7

54 Nyakeriga AM Williams TN Marsh K Wambua S Perlmann H Perlmann P Grandien A Troye-Blomberg M Cytokine mRNA expression and iron status in chil-dren living in a malaria endemic area Scand J Immunol 200561370ndash5

55 Smith HJ Meremikwu M Iron chelating agents for treating malaria Cochrane Database Syst Rev 2003CD001474

56 Weatherall DJ The global problem of genetic disease Ann Hum Biol 200532117ndash22

57 Williams TN Maitland K Bennett S Ganczakowski M Peto TE Newbold CI Bowden DK Weatherall DJ Clegg JB High incidence of malaria in alpha-thalassaemic children Nature 1996383522ndash5

58 Rees DC Williams TN Maitland K Clegg JB Weather-all DJ Alpha thalassaemia is associated with increased soluble transferrin receptor levels Br J Haematol 1998103365ndash9

59 Maitland K Williams TN Bennett S Newbold CI Peto TE Viji J Timothy R Clegg JB Weatherall DJ Bowden DK The interaction between Plasmodium falciparum and P vivax in children on Espiritu Santo island Van-uatu Trans R Soc Trop Med Hyg 199690614ndash20

60 Weatherall DJ Clegg JB Genetic variability in response to infection malaria and after Genes Immun 2002 3331ndash7

61 Parikh S Dorsey G Rosenthal PJ Host polymorphisms and the incidence of malaria in Ugandan children Am J Trop Med Hyg 200471750ndash3

62 Destro Bisol G Genetic resistance to malaria oxidative stress and hemoglobin oxidation Parassitologia 1999 41203ndash4

63 Cappadoro M Giribaldi G OrsquoBrien E Turrini F Mannu F Ulliers D Simula G Luzzatto L Arese P Early phago-cytosis of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes parasitized by Plasmodium falciparum may explain malaria protection in G6PD deficiency Blood 1998922527ndash34

64 Arese P Turrini F Schwarzer E Band 3complement-mediated recognition and removal of normally senes-cent and pathological human erythrocytes Cell Physiol Biochem 200516133ndash46

65 Atkinson SH Rockett K Sirugo G Bejon PA Fulford A OrsquoConnell M A Bailey R Kwiatkowski DP Prentice AM Seasonal Childhood Anaemia in West Africa Is Associated with the Haptoglobin 2-2 Genotype PLoS Med 20063e172

66 Cabrera G Cot M Migot-Nabias F Kremsner PG Deloron P Luty AJ The sickle cell trait is associated

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S539Iron metabolism and malaria

with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens J Infect Dis 20051911631ndash8

67 Williams TN Mwangi TW Roberts DJ Alexander ND Weatherall DJ Wambua S Kortok M Snow RW Marsh K An immune basis for malaria protection by the sickle cell trait PLoS Med 20052e128

68 Ayi K Turrini F Piga A Arese P Enhanced phagocyto-sis of ring-parasitized mutant erythrocytes a common mechanism that may explain protection against falci-parum malaria in sickle trait and beta-thalassemia trait Blood 20041043364ndash71

69 Roberts DJ Harris T Williams T The influence of inherited traits on malaria infection In Bellamy R ed Susceptibility to infectious diseases the importance of host genetics Cambridge Cambridge University Press 2004 139ndash84

70 Williams TN Mwangi TW Wambua S Alexander ND Kortok M Snow RW Marsh K Sickle cell trait and the risk of Plasmodium falciparum malaria and other child-hood diseases J Infect Dis 2005192178ndash86

71 Aidoo M Terlouw DJ Kolczak MS McElroy PD ter Kuile FO Kariuki S Nahlen BL Lal AA Udhayakumar V Protective effects of the sickle cell gene against malaria morbidity and mortality Lancet 20023591311ndash2

72 Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K Nega-tive epistasis between the malaria-protective effects of alpha+-thalassemia and the sickle cell trait Nat Genet 2005371253ndash7

73 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S Ascaso C Smith T MrsquoBoge B Greenwood BM The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS Trans R Soc Trop Med Hyg 199589289ndash92

74 Terlouw DJ Desai MR Wannemuehler KA Kariuki SK Pfeiffer CM Kager PA Shi YP Ter Kuile FO Relation between the response to iron supplementation and sickle cell hemoglobin phenotype in preschool children in western Kenya Am J Clin Nutr 200479466ndash72

75 Duffy PE Fried M Malaria in the pregnant woman Curr Top Microbiol Immunol 2005295169ndash200

76 Schellenberg D Menendez C Kahigwa E Aponte J Vidal J Tanner M Mshinda H Alonso P Intermittent treatment for malaria and anaemia control at time of routine vaccinations in Tanzanian infants a randomised placebo-controlled trial Lancet 20013571471ndash7

77 Schellenberg D Menendez C Aponte JJ Kahigwa E Tanner M Mshinda H Alonso P Intermittent preventive antimalarial treatment for Tanzanian infants follow-up to age 2 years of a randomised placebo-controlled trial Lancet 20053651481ndash3

78 OrsquoMeara WP Breman JG McKenzie FE The promise and potential challenges of intermittent preventive treat-ment for malaria in infants (IPTi) Malar J 2005433

79 White NJ Intermittent presumptive treatment for malaria PLoS Med 20052e3

80 Elagib AA Kider AO Akerstrom B Elbashir MI Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan Trans R Soc Trop Med Hyg 199892309ndash11

81 Minang JT Gyan BA Anchang JK Troye-Blomberg M Perlmann H Achidi EA Haptoglobin phenotypes and malaria infection in pregnant women at delivery in western Cameroon Acta Trop 200490107ndash14

82 Quaye IK Ekuban FA Goka BQ Adabayeri V Kurtzhals JA Gyan B Ankrah NA Hviid L Akanmori BD Hap-toglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria Trans R Soc Trop Med Hyg 200094216ndash9

83 Singh IP Walter H Bhasin MK Bhardwaj V Sudhakar K Genetic markers and malaria Observations in Gujarat India Hum Hered 19863631ndash6

84 Aucan C Walley AJ Greenwood BM Hill AV Hap-toglobin genotypes are not associated with resistance to severe malaria in The Gambia Trans R Soc Trop Med Hyg 200296327ndash8

85 Bienzle U Eggelte TA Adjei LA Dietz E Ehrhardt S Cramer JP Otchwemah RN Mockenhaupt FP Limited influence of haptoglobin genotypes on severe malaria in Ghanaian children Trop Med Int Health 200510668ndash71

86 Takeda M Kikuchi M Ubalee R Na-Bangchang K Ruangweerayut R Shibahara S Imai S Hirayama K Microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with susceptibility to cerebral malaria in Myanmar Jpn J Infect Dis 2005 58268ndash71

87 Shankar AH Nutritional modulation of malaria mor-bidity and mortality J Infect Dis 2000182 Suppl 1 S37ndash53

88 Gera T Sachdev HP Effect of iron supplementation on incidence of infectious illness in children systematic review Bmj 20023251142

Page 11: Iron metabolism and malaria

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S534 A M Prentice et al

single-deletion α-thalassemia compared with normal children

In a prospective casendashcontrol study in Papua New Guinea α-thalassemic α+ndash homozygotes and α+ndash heterozygotes had a greatly decreased risk of severe malaria (incidence rate ratio = 04 and 066) compared with controls [9] Furthermore protection was also observed for hospitalization from other infections possibly suggesting an immune component to the pro-tection [60] although the reduction of severe malaria may reduce infectious sequelae by invasive bacte-rial disease In apparent contrast α-thalassemia has also been associated with an increased prevalence of uncomplicated malaria in Vanuatu particularly in very young children with P vivax [57] It was suggested that increased red cell turnover in these children increased susceptibility to P vivax [58] resulting in cross-species immunity to P falciparum in later life [59] A similar finding was reported for glucose-6-phosphate dehy-drogenase (G6PD) deficiency in a cohort study in Uganda in which many other potential risk factors for malarial infection were controlled for (age water source use of prophylaxis bednet usage and proxim-ity to mosquito breeding sites) Female heterozygotes for G6PD had a significantly increased incidence of uncomplicated malaria (IRR = 13 p = 03) and a trend for increased parasite densities similar trends were seen for hemizygote males This was different from the pattern observed for HbS heterozygotes who had a nonsignificantly decreased incidence of uncomplicated malaria and decreased parasite densities [61]

A mechanism that has been suggested for G6PD defi-ciency and that may also be applicable to sickle (HbAS) and thalassemic cells involves decreased oxidative protection (G6PD) or increased constitutive oxidative stress of these cells (HbAS αβ thalassemias) especially when infected resulting in increased clearance of the cells from non-malaria-specific immune mechanisms essentially the same as the normal removal of old ldquosenescentrdquo red cells by phagocytes [62ndash64] It has been proposed that such a mechanism could prevent parasitemias from reaching critically high densities and therefore protect from severe malaria and also facilitate the development of antibody repertoires in children from the maintenance of low-grade infections in young children [65ndash67] In a slight modification of this hypothesis the increased phagocytic removal of early ring-stage infected cellsmdashcompared with schizonts and trophozoitesmdashhas been demonstrated for G6PD β-thalassemic and HbAS cells in vitro but not for α-thalassemic infected cells [68] The phagocytosis of ring compared with later stages may be advantageous since rings contain less hemozoin the buildup of which in monocytes has been associated with decreased func-tion Additionally the reduction of the later stages of parasite development may reduce the development of severe symptoms such as cerebral malaria from

reduced endothelial adhesion of late-stage infected red blood cells to receptors such as intracellular adhesion molecule-1 (ICAM-1)

The epidemiological evidence for a protective effect of HbAS suggests that the protective effects are great-est for severe disease (reviewed by Roberts et al [69]) In the most comprehensive study to date a detailed prospective cohort in two Kenyan populations it was reported that HbS heterozygotes had a significantly decreased risk of mild clinical malaria as assessed by active surveillance (50 decreased risk 95 confi-dence interval [CI] 26 to 67]) a 75 (95 CI 84 to 61) decreased risk of hospital admission for malaria and a 90 [95 CI 3 to 99] decreased risk of severe malaria (severe malarial anemia cerebral malaria or complicated malaria) [70] There was no effect of HbAS on the risk of asymptomatic infec-tions or of parasite density in asymptomatic infections assessed at four cross-sectional surveys There were significant decreases in parasite densities for all of the other categories of infection Additionally in this study unlike another in western Kenya [71] the protection was specific to malaria and did not extend to other common childhood infections including respiratory infections gastroenteritis and helminth infections

What influence the hemoglobinopathic and other polymorphisms may have on the effect of iron sup-plementation on malarial susceptibility is potentially dependent on the extent and mechanisms of protection from infection in the different genotypesmdashinfluences that are likely to be further complicated by differential effects according to age and malarial exposure and effects of coinheritance [72] The coinheritance of the HbS G6PD deficiency and α-thalassemia deletion alle-les is likely to be prevalent in sub-Saharan populations making the study of such effects in real populations extremely difficult by requiring very large sample sizes and complex statistical modeling

To the authorsrsquo knowledge only two published randomized controlled trials of iron supplementation have assessed the effects by genotypemdashin both cases by HbAS versus HbAA [73 74]

In the first trial involving Traditional Birth Attend-ant-administered routine iron supplementation to multigravid Gambian pregnant women Menendez et al [73] reported that although overall there were significant beneficial effects on hemoglobin and packed cell volume (PCV) and on birthweight these effects were entirely accounted for by women with the HbAA phenotype (N = 402 vs N = 98) whereas iron-supplemented HbAS women had lower HB PCV and birthweight than HbAA women receiving placebo Furthermore even in this relatively small study these interactions were statistically significant (p lt 01 for hematological indices at delivery baseline measurements as a covariate p lt 03 for birthweight maternal height included as a covariate) Overall

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S535Iron metabolism and malaria

there was no reported increase in susceptibility to malaria as assessed by the prevalence of peripheral malaria at late pregnancy and delivery or by placental histology Yet iron-supplemented HbAS women had an increased prevalence of placental malaria (76 [2229]) compared with iron-supplemented HbAA women (53 [83158]) placebo-treated HbAA women (59 [91154]) or placebo-treated HbAS women (58 [1933]) At the time of this study IPT prophylaxis was recommended only for primigravid pregnant women in the Gambia hence the choice of the study population What the effects of iron supplementation might be in either primigravidae or multigravidae receiving IPTmdashwhich is now recommended for all pregnant women in malaria-endemic countriesmdashhas not been assessed The protection afforded by the HbAS genotype is likely to vary according to gravidity and malarial endemic-ity In areas of high transmission the majority of the increased risk is borne by primigravidae whereas in areas of lower and highly defined seasonal transmis-sion the increased risk extends to a greater number of pregnancies [75] The protective effect of HbAS is thought to be greatest in relatively nonimmune young children who have not yet developed acquired immunity by exposure to a variety of clonal variants of P falciparum and therefore have not developed a full antibody repertoire to the variant surface antigens (VSA) expressed on the cell surfaces of parasitized red blood cells

In the second trial the effect of the HbAS phenotype on the response to iron supplementation in children was assessed in a subanalysis of a 2 times 2 randomized controlled trial of iron supplementation and inter-mittent preventive treatment (IPT) for malaria using sulfadoxinendashpyrimethamine in anemic Kenyan chil-dren (hemoglobin 7 to 109 gdL) [74] There was no reported increase in the susceptibility to clinical malaria or the prevalence of parasitemia at monthly screening associated with the iron supplementation alone or with IPT [16] whereas IPT plus iron was the most effective in increasing hemoglobin concentrations There were no significant statistical interactions between HbASAA phenotypes and treatment group However there was a nonsignificant increase in the incidence rate ratio of clinical malaria in the HbAS group not receiv-ing IPT during the 12 weeks of follow-up (IRR = 416 95 CI 05 to 346) and increased geometric mean parasite density in both groups but by far the biggest difference was seen in the group receiving IPT (6203 vs 1853 p = 08 for the interaction) The authors acknowledge that the number of clinical events was very small and that these findings would need veri-fication in a larger study since the number of HbAS individuals (approximately 25 to 30) in each treatment group versus approximately 100 HbAA individuals plus the short follow-up time means that the study was grossly underpowered to assess these outcomes If this

effect is real then the age group studied in this trial (2 to 36 months with 78 lt 18 months) should include the most affected although greater effects might be observed in areas of lower transmission and therefore also in a greater age range of children The results of these two trials warrant urgent further trials or retro-spective analysis of prior trials with sufficient power and detail to make firm conclusions on the effects of common polymorphisms on the response to iron sup-plementation which may be expected to vary by age group and transmission intensity

Clinical trials of IPT during infancy (IPTi) have demonstrated a reduction in the prevalence of anemia in young children in malaria-endemic areas [16 18 38 76] and in some trials a reduction in the incidence of clinical malaria [38 76] and morbidity and mortality in the first year of life [38 77] However the effects may vary depending on the timing of dosing choice of drug local levels of resistance and levels of transmission [78 79] On the basis of our analysis above the impact of IPTi plus iron supplementation may be modulated by levels of hemoglobinopathies and therefore suba-nalyses of these studies should be performed according to genotype wherever possible

Interactions of polymorphisms in host iron metabolism and regulatory proteins with malaria

Polymorphisms of haptoglobin a plasma protein that binds free hemoglobin released from lysed red blood cells recirculating the heme portion to the bone marrow through monocyte and macrophage uptake via CD136 have also been associated with malarial outcomes although reports are conflicting Hap-toglobin exists as three common phenotypes Hp1-1 1-2 and 2-2 In case-control studies in India Sudan Ghana and Cameroon the Hp2-2 phenotype has been associated with protection from severe malaria and placental infection [80ndash83] However two studies that have assessed associations with haptoglobin genotypes did not report any associations [84 85] In a cohort study in Gambian children the Hp2-2 genotype was associated with a greater drop in hemoglobin concen-trations across a malarial transmission season [65] The authors proposed that this effect may have been mediated through an increased prevalence of asymp-tomatic infection observed in the Hp2-2 group which contributed to anemia but could provide protection against severe malaria Interestingly similar but smaller drops in hemoglobin concentration were also observed for heterozygotes for G6PD and HbS We are currently analyzing the effects of low-dose iron supplementation during a malarial transmission season in a similar cohort of children

Inducible heme oxygenase (iHO-1) catalyzes the

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S536 A M Prentice et al

breakdown of heme to generate iron carbon monoxide and biliverdin and is expressed in monocytes and mac-rophages among other cells Biliverdin is subsequently degraded to bilirubin which has potent antioxidant effects Microsatellite polymorphisms in the number of tandem repeats in the promoter of iHO-1 have been variously associated with increased and decreased oxidant stress in various disease pathologies However in a case-control study of cerebral malaria patients in Myanmar homozygotes for the short number of repeats (lt 28) previously associated with higher levels of transcription of iHO-1 were significantly more likely to have cerebral malaria than uncomplicated malaria (odds ratio 314 p = 008) [86] It is not clear how this effect may be mediated but it is possible that it results from increased levels of free iron and resulting oxidant stress

In summary the mechanisms by which various genetic polymorphisms interact with malarial infec-tion are still not clear Furthermore it is not clear how they may affect a possible relationship between iron and malaria especially in relation to supplementation which should be differentiated from that of iron status The current evidence suggests that the heterozygous states of the hemoglobinopathies do not protect against malaria by a simple mechanism involving iron with-holding from the pathogen However the effects of iron supplementation in individuals with the most common polymorphisms should be carefully evaluated taking into account differences in transmission intensity and iron status at baseline

Conclusions

The evidence reviewed above tends to substantiate the concerns raised by the recent Pemba trial that universal administration of iron to children in malarious areas may be associated with adverse outcomes The mecha-nism by which this occurs is far from clear and merits

further research to test whether other chemical forms of supplementary iron might carry less risk There is also evidence that the risk profile will be altered by host genetic variations in hemoglobinopathies G6PD and genes regulating iron metabolism However these insights are not of great practical value because population screening and targeted supplementation programs are not feasible in the areas where iron defi-ciency is most prevalent Likewise the evidence that anemic children are probably at low risk for any adverse outcomes associated with iron supplementation implies a need for prescreening that may not be cost-effective or logistically feasible in developing-country settings

The evidence is fairly clear that malaria causes anemia by diverting iron away from bone marrow and erythropoiesis as part of the inflammatory response and hence iron administration alone is not likely to be the most effective means of combating the anemia Other therapeutic paradigms that combat the inflam-mation and adjust the timing of iron administra-tion to children recovering from malaria should be researched

We suggest that further research is still required to confirm the apparent relationships between iron status and malaria and that such studies should also focus on the underlying mechanisms of the putative interaction This might be achieved through the establishment of a multicountry collaboration to standardize protocols both for iron-supplementation interventions and for the assessment of iron and malaria status indicators Standardizing protocols across variations in age groups malaria transmission patterns and genetic distribu-tions of hemoglobinopathies will provide the evidence for a more targeted approach to policies of prevention and treatment of anemia in malaria-endemic regions

Until this evidence is gathered we recommend that iron supplementation in malarious areas must be accompanied by effective systems for ensuring univer-sal rapid access to diagnosis and treatment of malaria or by preventive therapy

References

1 WHO UNICEF Focusing on anaemia Towards an integrated approach for effective anaemia control Joint WHO UNICEF Statement Geneva Joint WHO UNICEF Statement 2004

2 Oppenheimer SJ Iron and its relation to immunity and infectious disease J Nutr 2001131616Sndash33S discussion 33Sndash35S

3 Murray MJ Murray AB Murray NJ Murray MB Diet and cerebral malaria the effect of famine and refeeding Am J Clin Nutr 19783157ndash61

4 Nyakeriga AM Troye-Blomberg M Dorfman JR Alexander ND Back R Kortok M Chemtai AK Marsh K Williams TN Iron deficiency and malaria among children living on the coast of Kenya J Infect Dis 2004 190439ndash47

5 Oppenheimer SJ Macfarlane SB Moody JB Bunari O Hendrickse RG Effect of iron prophylaxis on morbidity due to infectious disease report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 1986 80596ndash602

6 Shipton D Association between haemoglobin level and susceptibility to malaria a study of Gambian children [MSc dissertation] London London School of Hygiene and Tropical Medicine 2004

7 Snow RW Byass P Shenton FC Greenwood BM The relationship between anthropometric measurements and measurements of iron status and susceptibility to malaria in Gambian children Trans R Soc Trop Med Hyg 199185584ndash9

8 Asobayire FS Adou P Davidsson L Cook JD Hurrell

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S537Iron metabolism and malaria

RF Prevalence of iron deficiency with and without concurrent anemia in population groups with high prevalences of malaria and other infections a study in Cote drsquoIvoire Am J Clin Nutr 200174776ndash82

9 Allen SJ OrsquoDonnell A Alexander ND Alpers MP Peto TE Clegg JB Weatherall DJ alpha+-Thalassemia protects children against disease caused by other infec-tions as well as malaria Proc Natl Acad Sci U S A 1997 9414736ndash41

10 Murray MJ Murray AB Murray MB Murray CJ The adverse effect of iron repletion on the course of certain infections Br Med J 197821113ndash5

11 Smith AW Hendrickse RG Harrison C Hayes RJ Greenwood BM The effects on malaria of treatment of iron-deficiency anaemia with oral iron in Gambian children Ann Trop Paediatr 1989917ndash23

12 Oppenheimer SJ Gibson FD Macfarlane SB Moody JB Harrison C Spencer A Bunari O Iron supplementation increases prevalence and effects of malaria report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 198680603ndash12

13 Byles AB Drsquosa A Reduction of reaction due to iron dextran infusion using chloroquine Br Med J 19703625ndash7

14 Berger J Dyck JL Galan P Aplogan A Schneider D Traissac P Hercberg S Effect of daily iron supplementa-tion on iron status cell-mediated immunity and inci-dence of infections in 6ndash36 month old Togolese children Eur J Clin Nutr 20005429ndash35

15 Chippaux JP Schneider D Aplogan A Dyck JL Berger J [Effects of iron supplementation on malaria infection] Bull Soc Pathol Exot 19918454ndash62

16 Desai MR Mei JV Kariuki SK Wannemuehler KA Phil-lips-Howard PA Nahlen BL Kager PA Vulule JM ter Kuile FO Randomized controlled trial of daily iron sup-plementation and intermittent sulfadoxine-pyrimeth-amine for the treatment of mild childhood anemia in western Kenya J Infect Dis 2003187658ndash66

17 Nwanyanwu OC Ziba C Kazembe PN Gamadzi G Gandwe J Redd SC The effect of oral iron therapy during treatment for Plasmodium falciparum malaria with sulphadoxine-pyrimethamine on Malawian chil-dren under 5 years of age Ann Trop Med Parasitol 199690589ndash95

18 Verhoef H West CE Nzyuko SM de Vogel S van der Valk R Wanga MA Kuijsten A Veenemans J Kok FJ Intermittent administration of iron and sulfadoxine-py-rimethamine to control anaemia in Kenyan children a randomised controlled trial Lancet 2002360908ndash14

19 van den Hombergh J Dalderop E Smit Y Does iron therapy benefit children with severe malaria-associated anaemia A clinical trial with 12 weeks supplementation of oral iron in young children from the Turiani Division Tanzania J Trop Pediatr 199642220ndash7

20 Lawless JW Latham MC Stephenson LS Kinoti SN Pertet AM Iron supplementation improves appetite and growth in anemic Kenyan primary school children J Nutr 1994124645ndash54

21 Mebrahtu T Stoltzfus RJ Chwaya HM Jape JK Savioli L Montresor A Albonico M Tielsch JM Low-dose daily iron supplementation for 12 months does not increase the prevalence of malarial infection or den-sity of parasites in young Zanzibari children J Nutr 20041343037ndash41

22 Menendez C Kahigwa E Hirt R Vounatsou P Aponte JJ Font F Acosta CJ Schellenberg DM Galindo CM Kimario J Urassa H Brabin B Smith TA Kitua AY Tanner M Alonso PL Randomised placebo-controlled trial of iron supplementation and malaria chemoproph-ylaxis for prevention of severe anaemia and malaria in Tanzanian infants Lancet 1997350844ndash50

23 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S MrsquoBoge B Greenwood BM The effects of iron supplementation during pregnancy given by traditional birth attendants on the prevalence of anaemia and malaria Trans R Soc Trop Med Hyg 199488590ndash3

24 van Hensbroek MB Morris-Jones S Meisner S Jaffar S Bayo L Dackour R Phillips C Greenwood BM Iron but not folic acid combined with effective antimalarial therapy promotes haematological recovery in African children after acute falciparum malaria Trans R Soc Trop Med Hyg 199589672ndash6

25 Sazawal S Black RE Ramsan M Chwaya HM Stoltzfus RJ Dutta A Dhingra U Kabole I Deb S Othman MK Kabole FM Effects of routine prophylactic supplemen-tation with iron and folic acid on admission to hospital and mortality in preschool children in a high malaria transmission setting community-based randomised placebo-controlled trial Lancet 2006367133ndash43

26 Harvey PW Heywood PF Nesheim MC Galme K Zegans M Habicht JP Stephenson LS Radimer KL Brabin B Forsyth K et al The effect of iron therapy on malarial infection in Papua New Guinean schoolchil-dren Am J Trop Med Hyg 19894012ndash8

27 Andrews NC Iron homeostasis insights from genetics and animal models Nat Rev Genet 20001208ndash17

28 Kristiansen M Graversen JH Jacobsen C Sonne O Hoffman HJ Law SK Moestrup SK Identification of the haemoglobin scavenger receptor Nature 2001409 198ndash201

29 Wickramasinghe SN Abdalla SH Blood and bone marrow changes in malaria Baillieres Best Pract Res Clin Haematol 200013277ndash99

30 Phillips RE Looareesuwan S Warrell DA Lee SH Karbwang J Warrell MJ White NJ Swasdichai C Weatherall DJ The importance of anaemia in cerebral and uncomplicated falciparum malaria role of compli-cations dyserythropoiesis and iron sequestration Q J Med 198658305ndash23

31 Abdalla S Weatherall DJ Wickramasinghe SN Hughes M The anaemia of P falciparum malaria Br J Haematol 198046171ndash83

32 Sen R Bhatnagar BM Singh U Yadav MS Sehgal PK Patterns of erythropoiesis and anaemia in malaria J Commun Dis 199022247ndash53

33 Srichaikul T Wasanasomsithi M Poshyachinda V Panikbutr N Rabieb T Ferrokinetic studies and eryth-ropoiesis in malaria Arch Intern Med 1969124623ndash8

34 Das BS Thurnham DI Das DB Influence of malaria on markers of iron status in children implications for interpreting iron status in malaria-endemic communi-ties Br J Nutr 199778751ndash60

35 Menendez C Quinto LL Kahigwa E Alvarez L Fern-andez R Gimenez N Schellenberg D Aponte JJ Tanner M Alonso PL Effect of malaria on soluble transferrin receptor levels in Tanzanian infants Am J Trop Med Hyg 200165138ndash42

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S538 A M Prentice et al

36 Stoltzfus RJ Chwaya HM Montresor A Albonico M Savioli L Tielsch JM Malaria hookworms and recent fever are related to anemia and iron status indicators in 0- to 5-y old Zanzibari children and these relationships change with age J Nutr 20001301724ndash33

37 Stoltzfus RJ Chwaya HM Albonico M Schulze KJ Savioli L Tielsch JM Serum ferritin erythrocyte pro-toporphyrin and hemoglobin are valid indicators of iron status of school children in a malaria-holoendemic population J Nutr 1997127293ndash8

38 Massaga JJ Kitua AY Lemnge MM Akida JA Malle LN Ronn AM Theander TG Bygbjerg IC Effect of intermittent treatment with amodiaquine on anaemia and malarial fevers in infants in Tanzania a randomised placebo-controlled trial Lancet 20033611853ndash60

39 Verhoef H West CE Kraaijenhagen R Nzyuko SM King R Mbandi MM van Laatum S Hogervorst R Schep C Kok FJ Malarial anemia leads to adequately increased erythropoiesis in asymptomatic Kenyan children Blood 20021003489ndash94

40 Stoltzfus RJ Chway HM Montresor A Tielsch JM Jape JK Albonico M Savioli L Low dose daily iron supplementation improves iron status and appetite but not anemia whereas quarterly anthelminthic treatment improves growth appetite and anemia in Zanzibari preschool children J Nutr 2004134348ndash56

41 Kurtzhals JA Addae MM Akanmori BD Dunyo S Koram KA Appawu MA Nkrumah FK Hviid L Anae-mia caused by asymptomatic Plasmodium falciparum infection in semi-immune African schoolchildren Trans R Soc Trop Med Hyg 199993623ndash7

42 Loyevsky M John C Dickens B Hu V Miller JH Gordeuk VR Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators Mol Biochem Parasitol 199910143ndash59

43 Scholl PF Tripathi AK Sullivan DJ Bioavailable iron and heme metabolism in Plasmodium falciparum Curr Top Microbiol Immunol 2005295293ndash324

44 Darbari D Loyevsky M Gordeuk V Kark JA Castro O Rana S Apprey V Kurantsin-Mills J Fluorescence meas-urements of the labile iron pool of sickle erythrocytes Blood 2003102357ndash64

45 Ginsburg H Iron acquisition by Plasmodium spp Para-sitol Today 199915466

46 Atamna H Ginsburg H Heme degradation in the presence of glutathione A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells J Biol Chem 199527024876ndash83

47 Gabay T Ginsburg H Hemoglobin denaturation and iron release in acidified red blood cell lysatemdasha possible source of iron for intraerythrocytic malaria parasites Exp Parasitol 199377261ndash72

48 Iyer JK Shi L Shankar AH Sullivan DJ Jr Zinc pro-toporphyrin IX binds heme crystals to inhibit the proc-ess of crystallization in Plasmodium falciparum Mol Med 20039175ndash82

49 Cabantchik ZI Moody-Haupt S Gordeuk VR Iron che-lators as anti-infectives malaria as a paradigm FEMS Immunol Med Microbiol 199926289ndash98

50 Hershko C Control of disease by selective iron deple-tion a novel therapeutic strategy utilizing iron chelators Baillieres Clin Haematol 19947965ndash1000

51 Pradines B Tall A Ramiandrasoa F Spiegel A Sokhna C Fusai T Mosnier J Daries W Trape JF Kunesch G Parzy D Rogier C In vitro activity of iron-binding compounds against Senegalese isolates of Plasmodium falciparum J Antimicrob Chemother 2006571093ndash9

52 Meshnick SR Yang YZ Lima V Kuypers F Kam-chonwongpaisan S Yuthavong Y Iron-dependent free radical generation from the antimalarial agent artem-isinin (qinghaosu) Antimicrob Agents Chemother 1993371108ndash14

53 Golenser J Domb A Mordechai-Daniel T Leshem B Luty A Kremsner P Iron chelators correlation between effects on Plasmodium spp and immune functions J Parasitol 200692170ndash7

54 Nyakeriga AM Williams TN Marsh K Wambua S Perlmann H Perlmann P Grandien A Troye-Blomberg M Cytokine mRNA expression and iron status in chil-dren living in a malaria endemic area Scand J Immunol 200561370ndash5

55 Smith HJ Meremikwu M Iron chelating agents for treating malaria Cochrane Database Syst Rev 2003CD001474

56 Weatherall DJ The global problem of genetic disease Ann Hum Biol 200532117ndash22

57 Williams TN Maitland K Bennett S Ganczakowski M Peto TE Newbold CI Bowden DK Weatherall DJ Clegg JB High incidence of malaria in alpha-thalassaemic children Nature 1996383522ndash5

58 Rees DC Williams TN Maitland K Clegg JB Weather-all DJ Alpha thalassaemia is associated with increased soluble transferrin receptor levels Br J Haematol 1998103365ndash9

59 Maitland K Williams TN Bennett S Newbold CI Peto TE Viji J Timothy R Clegg JB Weatherall DJ Bowden DK The interaction between Plasmodium falciparum and P vivax in children on Espiritu Santo island Van-uatu Trans R Soc Trop Med Hyg 199690614ndash20

60 Weatherall DJ Clegg JB Genetic variability in response to infection malaria and after Genes Immun 2002 3331ndash7

61 Parikh S Dorsey G Rosenthal PJ Host polymorphisms and the incidence of malaria in Ugandan children Am J Trop Med Hyg 200471750ndash3

62 Destro Bisol G Genetic resistance to malaria oxidative stress and hemoglobin oxidation Parassitologia 1999 41203ndash4

63 Cappadoro M Giribaldi G OrsquoBrien E Turrini F Mannu F Ulliers D Simula G Luzzatto L Arese P Early phago-cytosis of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes parasitized by Plasmodium falciparum may explain malaria protection in G6PD deficiency Blood 1998922527ndash34

64 Arese P Turrini F Schwarzer E Band 3complement-mediated recognition and removal of normally senes-cent and pathological human erythrocytes Cell Physiol Biochem 200516133ndash46

65 Atkinson SH Rockett K Sirugo G Bejon PA Fulford A OrsquoConnell M A Bailey R Kwiatkowski DP Prentice AM Seasonal Childhood Anaemia in West Africa Is Associated with the Haptoglobin 2-2 Genotype PLoS Med 20063e172

66 Cabrera G Cot M Migot-Nabias F Kremsner PG Deloron P Luty AJ The sickle cell trait is associated

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S539Iron metabolism and malaria

with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens J Infect Dis 20051911631ndash8

67 Williams TN Mwangi TW Roberts DJ Alexander ND Weatherall DJ Wambua S Kortok M Snow RW Marsh K An immune basis for malaria protection by the sickle cell trait PLoS Med 20052e128

68 Ayi K Turrini F Piga A Arese P Enhanced phagocyto-sis of ring-parasitized mutant erythrocytes a common mechanism that may explain protection against falci-parum malaria in sickle trait and beta-thalassemia trait Blood 20041043364ndash71

69 Roberts DJ Harris T Williams T The influence of inherited traits on malaria infection In Bellamy R ed Susceptibility to infectious diseases the importance of host genetics Cambridge Cambridge University Press 2004 139ndash84

70 Williams TN Mwangi TW Wambua S Alexander ND Kortok M Snow RW Marsh K Sickle cell trait and the risk of Plasmodium falciparum malaria and other child-hood diseases J Infect Dis 2005192178ndash86

71 Aidoo M Terlouw DJ Kolczak MS McElroy PD ter Kuile FO Kariuki S Nahlen BL Lal AA Udhayakumar V Protective effects of the sickle cell gene against malaria morbidity and mortality Lancet 20023591311ndash2

72 Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K Nega-tive epistasis between the malaria-protective effects of alpha+-thalassemia and the sickle cell trait Nat Genet 2005371253ndash7

73 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S Ascaso C Smith T MrsquoBoge B Greenwood BM The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS Trans R Soc Trop Med Hyg 199589289ndash92

74 Terlouw DJ Desai MR Wannemuehler KA Kariuki SK Pfeiffer CM Kager PA Shi YP Ter Kuile FO Relation between the response to iron supplementation and sickle cell hemoglobin phenotype in preschool children in western Kenya Am J Clin Nutr 200479466ndash72

75 Duffy PE Fried M Malaria in the pregnant woman Curr Top Microbiol Immunol 2005295169ndash200

76 Schellenberg D Menendez C Kahigwa E Aponte J Vidal J Tanner M Mshinda H Alonso P Intermittent treatment for malaria and anaemia control at time of routine vaccinations in Tanzanian infants a randomised placebo-controlled trial Lancet 20013571471ndash7

77 Schellenberg D Menendez C Aponte JJ Kahigwa E Tanner M Mshinda H Alonso P Intermittent preventive antimalarial treatment for Tanzanian infants follow-up to age 2 years of a randomised placebo-controlled trial Lancet 20053651481ndash3

78 OrsquoMeara WP Breman JG McKenzie FE The promise and potential challenges of intermittent preventive treat-ment for malaria in infants (IPTi) Malar J 2005433

79 White NJ Intermittent presumptive treatment for malaria PLoS Med 20052e3

80 Elagib AA Kider AO Akerstrom B Elbashir MI Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan Trans R Soc Trop Med Hyg 199892309ndash11

81 Minang JT Gyan BA Anchang JK Troye-Blomberg M Perlmann H Achidi EA Haptoglobin phenotypes and malaria infection in pregnant women at delivery in western Cameroon Acta Trop 200490107ndash14

82 Quaye IK Ekuban FA Goka BQ Adabayeri V Kurtzhals JA Gyan B Ankrah NA Hviid L Akanmori BD Hap-toglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria Trans R Soc Trop Med Hyg 200094216ndash9

83 Singh IP Walter H Bhasin MK Bhardwaj V Sudhakar K Genetic markers and malaria Observations in Gujarat India Hum Hered 19863631ndash6

84 Aucan C Walley AJ Greenwood BM Hill AV Hap-toglobin genotypes are not associated with resistance to severe malaria in The Gambia Trans R Soc Trop Med Hyg 200296327ndash8

85 Bienzle U Eggelte TA Adjei LA Dietz E Ehrhardt S Cramer JP Otchwemah RN Mockenhaupt FP Limited influence of haptoglobin genotypes on severe malaria in Ghanaian children Trop Med Int Health 200510668ndash71

86 Takeda M Kikuchi M Ubalee R Na-Bangchang K Ruangweerayut R Shibahara S Imai S Hirayama K Microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with susceptibility to cerebral malaria in Myanmar Jpn J Infect Dis 2005 58268ndash71

87 Shankar AH Nutritional modulation of malaria mor-bidity and mortality J Infect Dis 2000182 Suppl 1 S37ndash53

88 Gera T Sachdev HP Effect of iron supplementation on incidence of infectious illness in children systematic review Bmj 20023251142

Page 12: Iron metabolism and malaria

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S535Iron metabolism and malaria

there was no reported increase in susceptibility to malaria as assessed by the prevalence of peripheral malaria at late pregnancy and delivery or by placental histology Yet iron-supplemented HbAS women had an increased prevalence of placental malaria (76 [2229]) compared with iron-supplemented HbAA women (53 [83158]) placebo-treated HbAA women (59 [91154]) or placebo-treated HbAS women (58 [1933]) At the time of this study IPT prophylaxis was recommended only for primigravid pregnant women in the Gambia hence the choice of the study population What the effects of iron supplementation might be in either primigravidae or multigravidae receiving IPTmdashwhich is now recommended for all pregnant women in malaria-endemic countriesmdashhas not been assessed The protection afforded by the HbAS genotype is likely to vary according to gravidity and malarial endemic-ity In areas of high transmission the majority of the increased risk is borne by primigravidae whereas in areas of lower and highly defined seasonal transmis-sion the increased risk extends to a greater number of pregnancies [75] The protective effect of HbAS is thought to be greatest in relatively nonimmune young children who have not yet developed acquired immunity by exposure to a variety of clonal variants of P falciparum and therefore have not developed a full antibody repertoire to the variant surface antigens (VSA) expressed on the cell surfaces of parasitized red blood cells

In the second trial the effect of the HbAS phenotype on the response to iron supplementation in children was assessed in a subanalysis of a 2 times 2 randomized controlled trial of iron supplementation and inter-mittent preventive treatment (IPT) for malaria using sulfadoxinendashpyrimethamine in anemic Kenyan chil-dren (hemoglobin 7 to 109 gdL) [74] There was no reported increase in the susceptibility to clinical malaria or the prevalence of parasitemia at monthly screening associated with the iron supplementation alone or with IPT [16] whereas IPT plus iron was the most effective in increasing hemoglobin concentrations There were no significant statistical interactions between HbASAA phenotypes and treatment group However there was a nonsignificant increase in the incidence rate ratio of clinical malaria in the HbAS group not receiv-ing IPT during the 12 weeks of follow-up (IRR = 416 95 CI 05 to 346) and increased geometric mean parasite density in both groups but by far the biggest difference was seen in the group receiving IPT (6203 vs 1853 p = 08 for the interaction) The authors acknowledge that the number of clinical events was very small and that these findings would need veri-fication in a larger study since the number of HbAS individuals (approximately 25 to 30) in each treatment group versus approximately 100 HbAA individuals plus the short follow-up time means that the study was grossly underpowered to assess these outcomes If this

effect is real then the age group studied in this trial (2 to 36 months with 78 lt 18 months) should include the most affected although greater effects might be observed in areas of lower transmission and therefore also in a greater age range of children The results of these two trials warrant urgent further trials or retro-spective analysis of prior trials with sufficient power and detail to make firm conclusions on the effects of common polymorphisms on the response to iron sup-plementation which may be expected to vary by age group and transmission intensity

Clinical trials of IPT during infancy (IPTi) have demonstrated a reduction in the prevalence of anemia in young children in malaria-endemic areas [16 18 38 76] and in some trials a reduction in the incidence of clinical malaria [38 76] and morbidity and mortality in the first year of life [38 77] However the effects may vary depending on the timing of dosing choice of drug local levels of resistance and levels of transmission [78 79] On the basis of our analysis above the impact of IPTi plus iron supplementation may be modulated by levels of hemoglobinopathies and therefore suba-nalyses of these studies should be performed according to genotype wherever possible

Interactions of polymorphisms in host iron metabolism and regulatory proteins with malaria

Polymorphisms of haptoglobin a plasma protein that binds free hemoglobin released from lysed red blood cells recirculating the heme portion to the bone marrow through monocyte and macrophage uptake via CD136 have also been associated with malarial outcomes although reports are conflicting Hap-toglobin exists as three common phenotypes Hp1-1 1-2 and 2-2 In case-control studies in India Sudan Ghana and Cameroon the Hp2-2 phenotype has been associated with protection from severe malaria and placental infection [80ndash83] However two studies that have assessed associations with haptoglobin genotypes did not report any associations [84 85] In a cohort study in Gambian children the Hp2-2 genotype was associated with a greater drop in hemoglobin concen-trations across a malarial transmission season [65] The authors proposed that this effect may have been mediated through an increased prevalence of asymp-tomatic infection observed in the Hp2-2 group which contributed to anemia but could provide protection against severe malaria Interestingly similar but smaller drops in hemoglobin concentration were also observed for heterozygotes for G6PD and HbS We are currently analyzing the effects of low-dose iron supplementation during a malarial transmission season in a similar cohort of children

Inducible heme oxygenase (iHO-1) catalyzes the

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S536 A M Prentice et al

breakdown of heme to generate iron carbon monoxide and biliverdin and is expressed in monocytes and mac-rophages among other cells Biliverdin is subsequently degraded to bilirubin which has potent antioxidant effects Microsatellite polymorphisms in the number of tandem repeats in the promoter of iHO-1 have been variously associated with increased and decreased oxidant stress in various disease pathologies However in a case-control study of cerebral malaria patients in Myanmar homozygotes for the short number of repeats (lt 28) previously associated with higher levels of transcription of iHO-1 were significantly more likely to have cerebral malaria than uncomplicated malaria (odds ratio 314 p = 008) [86] It is not clear how this effect may be mediated but it is possible that it results from increased levels of free iron and resulting oxidant stress

In summary the mechanisms by which various genetic polymorphisms interact with malarial infec-tion are still not clear Furthermore it is not clear how they may affect a possible relationship between iron and malaria especially in relation to supplementation which should be differentiated from that of iron status The current evidence suggests that the heterozygous states of the hemoglobinopathies do not protect against malaria by a simple mechanism involving iron with-holding from the pathogen However the effects of iron supplementation in individuals with the most common polymorphisms should be carefully evaluated taking into account differences in transmission intensity and iron status at baseline

Conclusions

The evidence reviewed above tends to substantiate the concerns raised by the recent Pemba trial that universal administration of iron to children in malarious areas may be associated with adverse outcomes The mecha-nism by which this occurs is far from clear and merits

further research to test whether other chemical forms of supplementary iron might carry less risk There is also evidence that the risk profile will be altered by host genetic variations in hemoglobinopathies G6PD and genes regulating iron metabolism However these insights are not of great practical value because population screening and targeted supplementation programs are not feasible in the areas where iron defi-ciency is most prevalent Likewise the evidence that anemic children are probably at low risk for any adverse outcomes associated with iron supplementation implies a need for prescreening that may not be cost-effective or logistically feasible in developing-country settings

The evidence is fairly clear that malaria causes anemia by diverting iron away from bone marrow and erythropoiesis as part of the inflammatory response and hence iron administration alone is not likely to be the most effective means of combating the anemia Other therapeutic paradigms that combat the inflam-mation and adjust the timing of iron administra-tion to children recovering from malaria should be researched

We suggest that further research is still required to confirm the apparent relationships between iron status and malaria and that such studies should also focus on the underlying mechanisms of the putative interaction This might be achieved through the establishment of a multicountry collaboration to standardize protocols both for iron-supplementation interventions and for the assessment of iron and malaria status indicators Standardizing protocols across variations in age groups malaria transmission patterns and genetic distribu-tions of hemoglobinopathies will provide the evidence for a more targeted approach to policies of prevention and treatment of anemia in malaria-endemic regions

Until this evidence is gathered we recommend that iron supplementation in malarious areas must be accompanied by effective systems for ensuring univer-sal rapid access to diagnosis and treatment of malaria or by preventive therapy

References

1 WHO UNICEF Focusing on anaemia Towards an integrated approach for effective anaemia control Joint WHO UNICEF Statement Geneva Joint WHO UNICEF Statement 2004

2 Oppenheimer SJ Iron and its relation to immunity and infectious disease J Nutr 2001131616Sndash33S discussion 33Sndash35S

3 Murray MJ Murray AB Murray NJ Murray MB Diet and cerebral malaria the effect of famine and refeeding Am J Clin Nutr 19783157ndash61

4 Nyakeriga AM Troye-Blomberg M Dorfman JR Alexander ND Back R Kortok M Chemtai AK Marsh K Williams TN Iron deficiency and malaria among children living on the coast of Kenya J Infect Dis 2004 190439ndash47

5 Oppenheimer SJ Macfarlane SB Moody JB Bunari O Hendrickse RG Effect of iron prophylaxis on morbidity due to infectious disease report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 1986 80596ndash602

6 Shipton D Association between haemoglobin level and susceptibility to malaria a study of Gambian children [MSc dissertation] London London School of Hygiene and Tropical Medicine 2004

7 Snow RW Byass P Shenton FC Greenwood BM The relationship between anthropometric measurements and measurements of iron status and susceptibility to malaria in Gambian children Trans R Soc Trop Med Hyg 199185584ndash9

8 Asobayire FS Adou P Davidsson L Cook JD Hurrell

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S537Iron metabolism and malaria

RF Prevalence of iron deficiency with and without concurrent anemia in population groups with high prevalences of malaria and other infections a study in Cote drsquoIvoire Am J Clin Nutr 200174776ndash82

9 Allen SJ OrsquoDonnell A Alexander ND Alpers MP Peto TE Clegg JB Weatherall DJ alpha+-Thalassemia protects children against disease caused by other infec-tions as well as malaria Proc Natl Acad Sci U S A 1997 9414736ndash41

10 Murray MJ Murray AB Murray MB Murray CJ The adverse effect of iron repletion on the course of certain infections Br Med J 197821113ndash5

11 Smith AW Hendrickse RG Harrison C Hayes RJ Greenwood BM The effects on malaria of treatment of iron-deficiency anaemia with oral iron in Gambian children Ann Trop Paediatr 1989917ndash23

12 Oppenheimer SJ Gibson FD Macfarlane SB Moody JB Harrison C Spencer A Bunari O Iron supplementation increases prevalence and effects of malaria report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 198680603ndash12

13 Byles AB Drsquosa A Reduction of reaction due to iron dextran infusion using chloroquine Br Med J 19703625ndash7

14 Berger J Dyck JL Galan P Aplogan A Schneider D Traissac P Hercberg S Effect of daily iron supplementa-tion on iron status cell-mediated immunity and inci-dence of infections in 6ndash36 month old Togolese children Eur J Clin Nutr 20005429ndash35

15 Chippaux JP Schneider D Aplogan A Dyck JL Berger J [Effects of iron supplementation on malaria infection] Bull Soc Pathol Exot 19918454ndash62

16 Desai MR Mei JV Kariuki SK Wannemuehler KA Phil-lips-Howard PA Nahlen BL Kager PA Vulule JM ter Kuile FO Randomized controlled trial of daily iron sup-plementation and intermittent sulfadoxine-pyrimeth-amine for the treatment of mild childhood anemia in western Kenya J Infect Dis 2003187658ndash66

17 Nwanyanwu OC Ziba C Kazembe PN Gamadzi G Gandwe J Redd SC The effect of oral iron therapy during treatment for Plasmodium falciparum malaria with sulphadoxine-pyrimethamine on Malawian chil-dren under 5 years of age Ann Trop Med Parasitol 199690589ndash95

18 Verhoef H West CE Nzyuko SM de Vogel S van der Valk R Wanga MA Kuijsten A Veenemans J Kok FJ Intermittent administration of iron and sulfadoxine-py-rimethamine to control anaemia in Kenyan children a randomised controlled trial Lancet 2002360908ndash14

19 van den Hombergh J Dalderop E Smit Y Does iron therapy benefit children with severe malaria-associated anaemia A clinical trial with 12 weeks supplementation of oral iron in young children from the Turiani Division Tanzania J Trop Pediatr 199642220ndash7

20 Lawless JW Latham MC Stephenson LS Kinoti SN Pertet AM Iron supplementation improves appetite and growth in anemic Kenyan primary school children J Nutr 1994124645ndash54

21 Mebrahtu T Stoltzfus RJ Chwaya HM Jape JK Savioli L Montresor A Albonico M Tielsch JM Low-dose daily iron supplementation for 12 months does not increase the prevalence of malarial infection or den-sity of parasites in young Zanzibari children J Nutr 20041343037ndash41

22 Menendez C Kahigwa E Hirt R Vounatsou P Aponte JJ Font F Acosta CJ Schellenberg DM Galindo CM Kimario J Urassa H Brabin B Smith TA Kitua AY Tanner M Alonso PL Randomised placebo-controlled trial of iron supplementation and malaria chemoproph-ylaxis for prevention of severe anaemia and malaria in Tanzanian infants Lancet 1997350844ndash50

23 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S MrsquoBoge B Greenwood BM The effects of iron supplementation during pregnancy given by traditional birth attendants on the prevalence of anaemia and malaria Trans R Soc Trop Med Hyg 199488590ndash3

24 van Hensbroek MB Morris-Jones S Meisner S Jaffar S Bayo L Dackour R Phillips C Greenwood BM Iron but not folic acid combined with effective antimalarial therapy promotes haematological recovery in African children after acute falciparum malaria Trans R Soc Trop Med Hyg 199589672ndash6

25 Sazawal S Black RE Ramsan M Chwaya HM Stoltzfus RJ Dutta A Dhingra U Kabole I Deb S Othman MK Kabole FM Effects of routine prophylactic supplemen-tation with iron and folic acid on admission to hospital and mortality in preschool children in a high malaria transmission setting community-based randomised placebo-controlled trial Lancet 2006367133ndash43

26 Harvey PW Heywood PF Nesheim MC Galme K Zegans M Habicht JP Stephenson LS Radimer KL Brabin B Forsyth K et al The effect of iron therapy on malarial infection in Papua New Guinean schoolchil-dren Am J Trop Med Hyg 19894012ndash8

27 Andrews NC Iron homeostasis insights from genetics and animal models Nat Rev Genet 20001208ndash17

28 Kristiansen M Graversen JH Jacobsen C Sonne O Hoffman HJ Law SK Moestrup SK Identification of the haemoglobin scavenger receptor Nature 2001409 198ndash201

29 Wickramasinghe SN Abdalla SH Blood and bone marrow changes in malaria Baillieres Best Pract Res Clin Haematol 200013277ndash99

30 Phillips RE Looareesuwan S Warrell DA Lee SH Karbwang J Warrell MJ White NJ Swasdichai C Weatherall DJ The importance of anaemia in cerebral and uncomplicated falciparum malaria role of compli-cations dyserythropoiesis and iron sequestration Q J Med 198658305ndash23

31 Abdalla S Weatherall DJ Wickramasinghe SN Hughes M The anaemia of P falciparum malaria Br J Haematol 198046171ndash83

32 Sen R Bhatnagar BM Singh U Yadav MS Sehgal PK Patterns of erythropoiesis and anaemia in malaria J Commun Dis 199022247ndash53

33 Srichaikul T Wasanasomsithi M Poshyachinda V Panikbutr N Rabieb T Ferrokinetic studies and eryth-ropoiesis in malaria Arch Intern Med 1969124623ndash8

34 Das BS Thurnham DI Das DB Influence of malaria on markers of iron status in children implications for interpreting iron status in malaria-endemic communi-ties Br J Nutr 199778751ndash60

35 Menendez C Quinto LL Kahigwa E Alvarez L Fern-andez R Gimenez N Schellenberg D Aponte JJ Tanner M Alonso PL Effect of malaria on soluble transferrin receptor levels in Tanzanian infants Am J Trop Med Hyg 200165138ndash42

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S538 A M Prentice et al

36 Stoltzfus RJ Chwaya HM Montresor A Albonico M Savioli L Tielsch JM Malaria hookworms and recent fever are related to anemia and iron status indicators in 0- to 5-y old Zanzibari children and these relationships change with age J Nutr 20001301724ndash33

37 Stoltzfus RJ Chwaya HM Albonico M Schulze KJ Savioli L Tielsch JM Serum ferritin erythrocyte pro-toporphyrin and hemoglobin are valid indicators of iron status of school children in a malaria-holoendemic population J Nutr 1997127293ndash8

38 Massaga JJ Kitua AY Lemnge MM Akida JA Malle LN Ronn AM Theander TG Bygbjerg IC Effect of intermittent treatment with amodiaquine on anaemia and malarial fevers in infants in Tanzania a randomised placebo-controlled trial Lancet 20033611853ndash60

39 Verhoef H West CE Kraaijenhagen R Nzyuko SM King R Mbandi MM van Laatum S Hogervorst R Schep C Kok FJ Malarial anemia leads to adequately increased erythropoiesis in asymptomatic Kenyan children Blood 20021003489ndash94

40 Stoltzfus RJ Chway HM Montresor A Tielsch JM Jape JK Albonico M Savioli L Low dose daily iron supplementation improves iron status and appetite but not anemia whereas quarterly anthelminthic treatment improves growth appetite and anemia in Zanzibari preschool children J Nutr 2004134348ndash56

41 Kurtzhals JA Addae MM Akanmori BD Dunyo S Koram KA Appawu MA Nkrumah FK Hviid L Anae-mia caused by asymptomatic Plasmodium falciparum infection in semi-immune African schoolchildren Trans R Soc Trop Med Hyg 199993623ndash7

42 Loyevsky M John C Dickens B Hu V Miller JH Gordeuk VR Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators Mol Biochem Parasitol 199910143ndash59

43 Scholl PF Tripathi AK Sullivan DJ Bioavailable iron and heme metabolism in Plasmodium falciparum Curr Top Microbiol Immunol 2005295293ndash324

44 Darbari D Loyevsky M Gordeuk V Kark JA Castro O Rana S Apprey V Kurantsin-Mills J Fluorescence meas-urements of the labile iron pool of sickle erythrocytes Blood 2003102357ndash64

45 Ginsburg H Iron acquisition by Plasmodium spp Para-sitol Today 199915466

46 Atamna H Ginsburg H Heme degradation in the presence of glutathione A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells J Biol Chem 199527024876ndash83

47 Gabay T Ginsburg H Hemoglobin denaturation and iron release in acidified red blood cell lysatemdasha possible source of iron for intraerythrocytic malaria parasites Exp Parasitol 199377261ndash72

48 Iyer JK Shi L Shankar AH Sullivan DJ Jr Zinc pro-toporphyrin IX binds heme crystals to inhibit the proc-ess of crystallization in Plasmodium falciparum Mol Med 20039175ndash82

49 Cabantchik ZI Moody-Haupt S Gordeuk VR Iron che-lators as anti-infectives malaria as a paradigm FEMS Immunol Med Microbiol 199926289ndash98

50 Hershko C Control of disease by selective iron deple-tion a novel therapeutic strategy utilizing iron chelators Baillieres Clin Haematol 19947965ndash1000

51 Pradines B Tall A Ramiandrasoa F Spiegel A Sokhna C Fusai T Mosnier J Daries W Trape JF Kunesch G Parzy D Rogier C In vitro activity of iron-binding compounds against Senegalese isolates of Plasmodium falciparum J Antimicrob Chemother 2006571093ndash9

52 Meshnick SR Yang YZ Lima V Kuypers F Kam-chonwongpaisan S Yuthavong Y Iron-dependent free radical generation from the antimalarial agent artem-isinin (qinghaosu) Antimicrob Agents Chemother 1993371108ndash14

53 Golenser J Domb A Mordechai-Daniel T Leshem B Luty A Kremsner P Iron chelators correlation between effects on Plasmodium spp and immune functions J Parasitol 200692170ndash7

54 Nyakeriga AM Williams TN Marsh K Wambua S Perlmann H Perlmann P Grandien A Troye-Blomberg M Cytokine mRNA expression and iron status in chil-dren living in a malaria endemic area Scand J Immunol 200561370ndash5

55 Smith HJ Meremikwu M Iron chelating agents for treating malaria Cochrane Database Syst Rev 2003CD001474

56 Weatherall DJ The global problem of genetic disease Ann Hum Biol 200532117ndash22

57 Williams TN Maitland K Bennett S Ganczakowski M Peto TE Newbold CI Bowden DK Weatherall DJ Clegg JB High incidence of malaria in alpha-thalassaemic children Nature 1996383522ndash5

58 Rees DC Williams TN Maitland K Clegg JB Weather-all DJ Alpha thalassaemia is associated with increased soluble transferrin receptor levels Br J Haematol 1998103365ndash9

59 Maitland K Williams TN Bennett S Newbold CI Peto TE Viji J Timothy R Clegg JB Weatherall DJ Bowden DK The interaction between Plasmodium falciparum and P vivax in children on Espiritu Santo island Van-uatu Trans R Soc Trop Med Hyg 199690614ndash20

60 Weatherall DJ Clegg JB Genetic variability in response to infection malaria and after Genes Immun 2002 3331ndash7

61 Parikh S Dorsey G Rosenthal PJ Host polymorphisms and the incidence of malaria in Ugandan children Am J Trop Med Hyg 200471750ndash3

62 Destro Bisol G Genetic resistance to malaria oxidative stress and hemoglobin oxidation Parassitologia 1999 41203ndash4

63 Cappadoro M Giribaldi G OrsquoBrien E Turrini F Mannu F Ulliers D Simula G Luzzatto L Arese P Early phago-cytosis of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes parasitized by Plasmodium falciparum may explain malaria protection in G6PD deficiency Blood 1998922527ndash34

64 Arese P Turrini F Schwarzer E Band 3complement-mediated recognition and removal of normally senes-cent and pathological human erythrocytes Cell Physiol Biochem 200516133ndash46

65 Atkinson SH Rockett K Sirugo G Bejon PA Fulford A OrsquoConnell M A Bailey R Kwiatkowski DP Prentice AM Seasonal Childhood Anaemia in West Africa Is Associated with the Haptoglobin 2-2 Genotype PLoS Med 20063e172

66 Cabrera G Cot M Migot-Nabias F Kremsner PG Deloron P Luty AJ The sickle cell trait is associated

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S539Iron metabolism and malaria

with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens J Infect Dis 20051911631ndash8

67 Williams TN Mwangi TW Roberts DJ Alexander ND Weatherall DJ Wambua S Kortok M Snow RW Marsh K An immune basis for malaria protection by the sickle cell trait PLoS Med 20052e128

68 Ayi K Turrini F Piga A Arese P Enhanced phagocyto-sis of ring-parasitized mutant erythrocytes a common mechanism that may explain protection against falci-parum malaria in sickle trait and beta-thalassemia trait Blood 20041043364ndash71

69 Roberts DJ Harris T Williams T The influence of inherited traits on malaria infection In Bellamy R ed Susceptibility to infectious diseases the importance of host genetics Cambridge Cambridge University Press 2004 139ndash84

70 Williams TN Mwangi TW Wambua S Alexander ND Kortok M Snow RW Marsh K Sickle cell trait and the risk of Plasmodium falciparum malaria and other child-hood diseases J Infect Dis 2005192178ndash86

71 Aidoo M Terlouw DJ Kolczak MS McElroy PD ter Kuile FO Kariuki S Nahlen BL Lal AA Udhayakumar V Protective effects of the sickle cell gene against malaria morbidity and mortality Lancet 20023591311ndash2

72 Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K Nega-tive epistasis between the malaria-protective effects of alpha+-thalassemia and the sickle cell trait Nat Genet 2005371253ndash7

73 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S Ascaso C Smith T MrsquoBoge B Greenwood BM The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS Trans R Soc Trop Med Hyg 199589289ndash92

74 Terlouw DJ Desai MR Wannemuehler KA Kariuki SK Pfeiffer CM Kager PA Shi YP Ter Kuile FO Relation between the response to iron supplementation and sickle cell hemoglobin phenotype in preschool children in western Kenya Am J Clin Nutr 200479466ndash72

75 Duffy PE Fried M Malaria in the pregnant woman Curr Top Microbiol Immunol 2005295169ndash200

76 Schellenberg D Menendez C Kahigwa E Aponte J Vidal J Tanner M Mshinda H Alonso P Intermittent treatment for malaria and anaemia control at time of routine vaccinations in Tanzanian infants a randomised placebo-controlled trial Lancet 20013571471ndash7

77 Schellenberg D Menendez C Aponte JJ Kahigwa E Tanner M Mshinda H Alonso P Intermittent preventive antimalarial treatment for Tanzanian infants follow-up to age 2 years of a randomised placebo-controlled trial Lancet 20053651481ndash3

78 OrsquoMeara WP Breman JG McKenzie FE The promise and potential challenges of intermittent preventive treat-ment for malaria in infants (IPTi) Malar J 2005433

79 White NJ Intermittent presumptive treatment for malaria PLoS Med 20052e3

80 Elagib AA Kider AO Akerstrom B Elbashir MI Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan Trans R Soc Trop Med Hyg 199892309ndash11

81 Minang JT Gyan BA Anchang JK Troye-Blomberg M Perlmann H Achidi EA Haptoglobin phenotypes and malaria infection in pregnant women at delivery in western Cameroon Acta Trop 200490107ndash14

82 Quaye IK Ekuban FA Goka BQ Adabayeri V Kurtzhals JA Gyan B Ankrah NA Hviid L Akanmori BD Hap-toglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria Trans R Soc Trop Med Hyg 200094216ndash9

83 Singh IP Walter H Bhasin MK Bhardwaj V Sudhakar K Genetic markers and malaria Observations in Gujarat India Hum Hered 19863631ndash6

84 Aucan C Walley AJ Greenwood BM Hill AV Hap-toglobin genotypes are not associated with resistance to severe malaria in The Gambia Trans R Soc Trop Med Hyg 200296327ndash8

85 Bienzle U Eggelte TA Adjei LA Dietz E Ehrhardt S Cramer JP Otchwemah RN Mockenhaupt FP Limited influence of haptoglobin genotypes on severe malaria in Ghanaian children Trop Med Int Health 200510668ndash71

86 Takeda M Kikuchi M Ubalee R Na-Bangchang K Ruangweerayut R Shibahara S Imai S Hirayama K Microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with susceptibility to cerebral malaria in Myanmar Jpn J Infect Dis 2005 58268ndash71

87 Shankar AH Nutritional modulation of malaria mor-bidity and mortality J Infect Dis 2000182 Suppl 1 S37ndash53

88 Gera T Sachdev HP Effect of iron supplementation on incidence of infectious illness in children systematic review Bmj 20023251142

Page 13: Iron metabolism and malaria

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S536 A M Prentice et al

breakdown of heme to generate iron carbon monoxide and biliverdin and is expressed in monocytes and mac-rophages among other cells Biliverdin is subsequently degraded to bilirubin which has potent antioxidant effects Microsatellite polymorphisms in the number of tandem repeats in the promoter of iHO-1 have been variously associated with increased and decreased oxidant stress in various disease pathologies However in a case-control study of cerebral malaria patients in Myanmar homozygotes for the short number of repeats (lt 28) previously associated with higher levels of transcription of iHO-1 were significantly more likely to have cerebral malaria than uncomplicated malaria (odds ratio 314 p = 008) [86] It is not clear how this effect may be mediated but it is possible that it results from increased levels of free iron and resulting oxidant stress

In summary the mechanisms by which various genetic polymorphisms interact with malarial infec-tion are still not clear Furthermore it is not clear how they may affect a possible relationship between iron and malaria especially in relation to supplementation which should be differentiated from that of iron status The current evidence suggests that the heterozygous states of the hemoglobinopathies do not protect against malaria by a simple mechanism involving iron with-holding from the pathogen However the effects of iron supplementation in individuals with the most common polymorphisms should be carefully evaluated taking into account differences in transmission intensity and iron status at baseline

Conclusions

The evidence reviewed above tends to substantiate the concerns raised by the recent Pemba trial that universal administration of iron to children in malarious areas may be associated with adverse outcomes The mecha-nism by which this occurs is far from clear and merits

further research to test whether other chemical forms of supplementary iron might carry less risk There is also evidence that the risk profile will be altered by host genetic variations in hemoglobinopathies G6PD and genes regulating iron metabolism However these insights are not of great practical value because population screening and targeted supplementation programs are not feasible in the areas where iron defi-ciency is most prevalent Likewise the evidence that anemic children are probably at low risk for any adverse outcomes associated with iron supplementation implies a need for prescreening that may not be cost-effective or logistically feasible in developing-country settings

The evidence is fairly clear that malaria causes anemia by diverting iron away from bone marrow and erythropoiesis as part of the inflammatory response and hence iron administration alone is not likely to be the most effective means of combating the anemia Other therapeutic paradigms that combat the inflam-mation and adjust the timing of iron administra-tion to children recovering from malaria should be researched

We suggest that further research is still required to confirm the apparent relationships between iron status and malaria and that such studies should also focus on the underlying mechanisms of the putative interaction This might be achieved through the establishment of a multicountry collaboration to standardize protocols both for iron-supplementation interventions and for the assessment of iron and malaria status indicators Standardizing protocols across variations in age groups malaria transmission patterns and genetic distribu-tions of hemoglobinopathies will provide the evidence for a more targeted approach to policies of prevention and treatment of anemia in malaria-endemic regions

Until this evidence is gathered we recommend that iron supplementation in malarious areas must be accompanied by effective systems for ensuring univer-sal rapid access to diagnosis and treatment of malaria or by preventive therapy

References

1 WHO UNICEF Focusing on anaemia Towards an integrated approach for effective anaemia control Joint WHO UNICEF Statement Geneva Joint WHO UNICEF Statement 2004

2 Oppenheimer SJ Iron and its relation to immunity and infectious disease J Nutr 2001131616Sndash33S discussion 33Sndash35S

3 Murray MJ Murray AB Murray NJ Murray MB Diet and cerebral malaria the effect of famine and refeeding Am J Clin Nutr 19783157ndash61

4 Nyakeriga AM Troye-Blomberg M Dorfman JR Alexander ND Back R Kortok M Chemtai AK Marsh K Williams TN Iron deficiency and malaria among children living on the coast of Kenya J Infect Dis 2004 190439ndash47

5 Oppenheimer SJ Macfarlane SB Moody JB Bunari O Hendrickse RG Effect of iron prophylaxis on morbidity due to infectious disease report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 1986 80596ndash602

6 Shipton D Association between haemoglobin level and susceptibility to malaria a study of Gambian children [MSc dissertation] London London School of Hygiene and Tropical Medicine 2004

7 Snow RW Byass P Shenton FC Greenwood BM The relationship between anthropometric measurements and measurements of iron status and susceptibility to malaria in Gambian children Trans R Soc Trop Med Hyg 199185584ndash9

8 Asobayire FS Adou P Davidsson L Cook JD Hurrell

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S537Iron metabolism and malaria

RF Prevalence of iron deficiency with and without concurrent anemia in population groups with high prevalences of malaria and other infections a study in Cote drsquoIvoire Am J Clin Nutr 200174776ndash82

9 Allen SJ OrsquoDonnell A Alexander ND Alpers MP Peto TE Clegg JB Weatherall DJ alpha+-Thalassemia protects children against disease caused by other infec-tions as well as malaria Proc Natl Acad Sci U S A 1997 9414736ndash41

10 Murray MJ Murray AB Murray MB Murray CJ The adverse effect of iron repletion on the course of certain infections Br Med J 197821113ndash5

11 Smith AW Hendrickse RG Harrison C Hayes RJ Greenwood BM The effects on malaria of treatment of iron-deficiency anaemia with oral iron in Gambian children Ann Trop Paediatr 1989917ndash23

12 Oppenheimer SJ Gibson FD Macfarlane SB Moody JB Harrison C Spencer A Bunari O Iron supplementation increases prevalence and effects of malaria report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 198680603ndash12

13 Byles AB Drsquosa A Reduction of reaction due to iron dextran infusion using chloroquine Br Med J 19703625ndash7

14 Berger J Dyck JL Galan P Aplogan A Schneider D Traissac P Hercberg S Effect of daily iron supplementa-tion on iron status cell-mediated immunity and inci-dence of infections in 6ndash36 month old Togolese children Eur J Clin Nutr 20005429ndash35

15 Chippaux JP Schneider D Aplogan A Dyck JL Berger J [Effects of iron supplementation on malaria infection] Bull Soc Pathol Exot 19918454ndash62

16 Desai MR Mei JV Kariuki SK Wannemuehler KA Phil-lips-Howard PA Nahlen BL Kager PA Vulule JM ter Kuile FO Randomized controlled trial of daily iron sup-plementation and intermittent sulfadoxine-pyrimeth-amine for the treatment of mild childhood anemia in western Kenya J Infect Dis 2003187658ndash66

17 Nwanyanwu OC Ziba C Kazembe PN Gamadzi G Gandwe J Redd SC The effect of oral iron therapy during treatment for Plasmodium falciparum malaria with sulphadoxine-pyrimethamine on Malawian chil-dren under 5 years of age Ann Trop Med Parasitol 199690589ndash95

18 Verhoef H West CE Nzyuko SM de Vogel S van der Valk R Wanga MA Kuijsten A Veenemans J Kok FJ Intermittent administration of iron and sulfadoxine-py-rimethamine to control anaemia in Kenyan children a randomised controlled trial Lancet 2002360908ndash14

19 van den Hombergh J Dalderop E Smit Y Does iron therapy benefit children with severe malaria-associated anaemia A clinical trial with 12 weeks supplementation of oral iron in young children from the Turiani Division Tanzania J Trop Pediatr 199642220ndash7

20 Lawless JW Latham MC Stephenson LS Kinoti SN Pertet AM Iron supplementation improves appetite and growth in anemic Kenyan primary school children J Nutr 1994124645ndash54

21 Mebrahtu T Stoltzfus RJ Chwaya HM Jape JK Savioli L Montresor A Albonico M Tielsch JM Low-dose daily iron supplementation for 12 months does not increase the prevalence of malarial infection or den-sity of parasites in young Zanzibari children J Nutr 20041343037ndash41

22 Menendez C Kahigwa E Hirt R Vounatsou P Aponte JJ Font F Acosta CJ Schellenberg DM Galindo CM Kimario J Urassa H Brabin B Smith TA Kitua AY Tanner M Alonso PL Randomised placebo-controlled trial of iron supplementation and malaria chemoproph-ylaxis for prevention of severe anaemia and malaria in Tanzanian infants Lancet 1997350844ndash50

23 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S MrsquoBoge B Greenwood BM The effects of iron supplementation during pregnancy given by traditional birth attendants on the prevalence of anaemia and malaria Trans R Soc Trop Med Hyg 199488590ndash3

24 van Hensbroek MB Morris-Jones S Meisner S Jaffar S Bayo L Dackour R Phillips C Greenwood BM Iron but not folic acid combined with effective antimalarial therapy promotes haematological recovery in African children after acute falciparum malaria Trans R Soc Trop Med Hyg 199589672ndash6

25 Sazawal S Black RE Ramsan M Chwaya HM Stoltzfus RJ Dutta A Dhingra U Kabole I Deb S Othman MK Kabole FM Effects of routine prophylactic supplemen-tation with iron and folic acid on admission to hospital and mortality in preschool children in a high malaria transmission setting community-based randomised placebo-controlled trial Lancet 2006367133ndash43

26 Harvey PW Heywood PF Nesheim MC Galme K Zegans M Habicht JP Stephenson LS Radimer KL Brabin B Forsyth K et al The effect of iron therapy on malarial infection in Papua New Guinean schoolchil-dren Am J Trop Med Hyg 19894012ndash8

27 Andrews NC Iron homeostasis insights from genetics and animal models Nat Rev Genet 20001208ndash17

28 Kristiansen M Graversen JH Jacobsen C Sonne O Hoffman HJ Law SK Moestrup SK Identification of the haemoglobin scavenger receptor Nature 2001409 198ndash201

29 Wickramasinghe SN Abdalla SH Blood and bone marrow changes in malaria Baillieres Best Pract Res Clin Haematol 200013277ndash99

30 Phillips RE Looareesuwan S Warrell DA Lee SH Karbwang J Warrell MJ White NJ Swasdichai C Weatherall DJ The importance of anaemia in cerebral and uncomplicated falciparum malaria role of compli-cations dyserythropoiesis and iron sequestration Q J Med 198658305ndash23

31 Abdalla S Weatherall DJ Wickramasinghe SN Hughes M The anaemia of P falciparum malaria Br J Haematol 198046171ndash83

32 Sen R Bhatnagar BM Singh U Yadav MS Sehgal PK Patterns of erythropoiesis and anaemia in malaria J Commun Dis 199022247ndash53

33 Srichaikul T Wasanasomsithi M Poshyachinda V Panikbutr N Rabieb T Ferrokinetic studies and eryth-ropoiesis in malaria Arch Intern Med 1969124623ndash8

34 Das BS Thurnham DI Das DB Influence of malaria on markers of iron status in children implications for interpreting iron status in malaria-endemic communi-ties Br J Nutr 199778751ndash60

35 Menendez C Quinto LL Kahigwa E Alvarez L Fern-andez R Gimenez N Schellenberg D Aponte JJ Tanner M Alonso PL Effect of malaria on soluble transferrin receptor levels in Tanzanian infants Am J Trop Med Hyg 200165138ndash42

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S538 A M Prentice et al

36 Stoltzfus RJ Chwaya HM Montresor A Albonico M Savioli L Tielsch JM Malaria hookworms and recent fever are related to anemia and iron status indicators in 0- to 5-y old Zanzibari children and these relationships change with age J Nutr 20001301724ndash33

37 Stoltzfus RJ Chwaya HM Albonico M Schulze KJ Savioli L Tielsch JM Serum ferritin erythrocyte pro-toporphyrin and hemoglobin are valid indicators of iron status of school children in a malaria-holoendemic population J Nutr 1997127293ndash8

38 Massaga JJ Kitua AY Lemnge MM Akida JA Malle LN Ronn AM Theander TG Bygbjerg IC Effect of intermittent treatment with amodiaquine on anaemia and malarial fevers in infants in Tanzania a randomised placebo-controlled trial Lancet 20033611853ndash60

39 Verhoef H West CE Kraaijenhagen R Nzyuko SM King R Mbandi MM van Laatum S Hogervorst R Schep C Kok FJ Malarial anemia leads to adequately increased erythropoiesis in asymptomatic Kenyan children Blood 20021003489ndash94

40 Stoltzfus RJ Chway HM Montresor A Tielsch JM Jape JK Albonico M Savioli L Low dose daily iron supplementation improves iron status and appetite but not anemia whereas quarterly anthelminthic treatment improves growth appetite and anemia in Zanzibari preschool children J Nutr 2004134348ndash56

41 Kurtzhals JA Addae MM Akanmori BD Dunyo S Koram KA Appawu MA Nkrumah FK Hviid L Anae-mia caused by asymptomatic Plasmodium falciparum infection in semi-immune African schoolchildren Trans R Soc Trop Med Hyg 199993623ndash7

42 Loyevsky M John C Dickens B Hu V Miller JH Gordeuk VR Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators Mol Biochem Parasitol 199910143ndash59

43 Scholl PF Tripathi AK Sullivan DJ Bioavailable iron and heme metabolism in Plasmodium falciparum Curr Top Microbiol Immunol 2005295293ndash324

44 Darbari D Loyevsky M Gordeuk V Kark JA Castro O Rana S Apprey V Kurantsin-Mills J Fluorescence meas-urements of the labile iron pool of sickle erythrocytes Blood 2003102357ndash64

45 Ginsburg H Iron acquisition by Plasmodium spp Para-sitol Today 199915466

46 Atamna H Ginsburg H Heme degradation in the presence of glutathione A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells J Biol Chem 199527024876ndash83

47 Gabay T Ginsburg H Hemoglobin denaturation and iron release in acidified red blood cell lysatemdasha possible source of iron for intraerythrocytic malaria parasites Exp Parasitol 199377261ndash72

48 Iyer JK Shi L Shankar AH Sullivan DJ Jr Zinc pro-toporphyrin IX binds heme crystals to inhibit the proc-ess of crystallization in Plasmodium falciparum Mol Med 20039175ndash82

49 Cabantchik ZI Moody-Haupt S Gordeuk VR Iron che-lators as anti-infectives malaria as a paradigm FEMS Immunol Med Microbiol 199926289ndash98

50 Hershko C Control of disease by selective iron deple-tion a novel therapeutic strategy utilizing iron chelators Baillieres Clin Haematol 19947965ndash1000

51 Pradines B Tall A Ramiandrasoa F Spiegel A Sokhna C Fusai T Mosnier J Daries W Trape JF Kunesch G Parzy D Rogier C In vitro activity of iron-binding compounds against Senegalese isolates of Plasmodium falciparum J Antimicrob Chemother 2006571093ndash9

52 Meshnick SR Yang YZ Lima V Kuypers F Kam-chonwongpaisan S Yuthavong Y Iron-dependent free radical generation from the antimalarial agent artem-isinin (qinghaosu) Antimicrob Agents Chemother 1993371108ndash14

53 Golenser J Domb A Mordechai-Daniel T Leshem B Luty A Kremsner P Iron chelators correlation between effects on Plasmodium spp and immune functions J Parasitol 200692170ndash7

54 Nyakeriga AM Williams TN Marsh K Wambua S Perlmann H Perlmann P Grandien A Troye-Blomberg M Cytokine mRNA expression and iron status in chil-dren living in a malaria endemic area Scand J Immunol 200561370ndash5

55 Smith HJ Meremikwu M Iron chelating agents for treating malaria Cochrane Database Syst Rev 2003CD001474

56 Weatherall DJ The global problem of genetic disease Ann Hum Biol 200532117ndash22

57 Williams TN Maitland K Bennett S Ganczakowski M Peto TE Newbold CI Bowden DK Weatherall DJ Clegg JB High incidence of malaria in alpha-thalassaemic children Nature 1996383522ndash5

58 Rees DC Williams TN Maitland K Clegg JB Weather-all DJ Alpha thalassaemia is associated with increased soluble transferrin receptor levels Br J Haematol 1998103365ndash9

59 Maitland K Williams TN Bennett S Newbold CI Peto TE Viji J Timothy R Clegg JB Weatherall DJ Bowden DK The interaction between Plasmodium falciparum and P vivax in children on Espiritu Santo island Van-uatu Trans R Soc Trop Med Hyg 199690614ndash20

60 Weatherall DJ Clegg JB Genetic variability in response to infection malaria and after Genes Immun 2002 3331ndash7

61 Parikh S Dorsey G Rosenthal PJ Host polymorphisms and the incidence of malaria in Ugandan children Am J Trop Med Hyg 200471750ndash3

62 Destro Bisol G Genetic resistance to malaria oxidative stress and hemoglobin oxidation Parassitologia 1999 41203ndash4

63 Cappadoro M Giribaldi G OrsquoBrien E Turrini F Mannu F Ulliers D Simula G Luzzatto L Arese P Early phago-cytosis of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes parasitized by Plasmodium falciparum may explain malaria protection in G6PD deficiency Blood 1998922527ndash34

64 Arese P Turrini F Schwarzer E Band 3complement-mediated recognition and removal of normally senes-cent and pathological human erythrocytes Cell Physiol Biochem 200516133ndash46

65 Atkinson SH Rockett K Sirugo G Bejon PA Fulford A OrsquoConnell M A Bailey R Kwiatkowski DP Prentice AM Seasonal Childhood Anaemia in West Africa Is Associated with the Haptoglobin 2-2 Genotype PLoS Med 20063e172

66 Cabrera G Cot M Migot-Nabias F Kremsner PG Deloron P Luty AJ The sickle cell trait is associated

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S539Iron metabolism and malaria

with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens J Infect Dis 20051911631ndash8

67 Williams TN Mwangi TW Roberts DJ Alexander ND Weatherall DJ Wambua S Kortok M Snow RW Marsh K An immune basis for malaria protection by the sickle cell trait PLoS Med 20052e128

68 Ayi K Turrini F Piga A Arese P Enhanced phagocyto-sis of ring-parasitized mutant erythrocytes a common mechanism that may explain protection against falci-parum malaria in sickle trait and beta-thalassemia trait Blood 20041043364ndash71

69 Roberts DJ Harris T Williams T The influence of inherited traits on malaria infection In Bellamy R ed Susceptibility to infectious diseases the importance of host genetics Cambridge Cambridge University Press 2004 139ndash84

70 Williams TN Mwangi TW Wambua S Alexander ND Kortok M Snow RW Marsh K Sickle cell trait and the risk of Plasmodium falciparum malaria and other child-hood diseases J Infect Dis 2005192178ndash86

71 Aidoo M Terlouw DJ Kolczak MS McElroy PD ter Kuile FO Kariuki S Nahlen BL Lal AA Udhayakumar V Protective effects of the sickle cell gene against malaria morbidity and mortality Lancet 20023591311ndash2

72 Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K Nega-tive epistasis between the malaria-protective effects of alpha+-thalassemia and the sickle cell trait Nat Genet 2005371253ndash7

73 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S Ascaso C Smith T MrsquoBoge B Greenwood BM The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS Trans R Soc Trop Med Hyg 199589289ndash92

74 Terlouw DJ Desai MR Wannemuehler KA Kariuki SK Pfeiffer CM Kager PA Shi YP Ter Kuile FO Relation between the response to iron supplementation and sickle cell hemoglobin phenotype in preschool children in western Kenya Am J Clin Nutr 200479466ndash72

75 Duffy PE Fried M Malaria in the pregnant woman Curr Top Microbiol Immunol 2005295169ndash200

76 Schellenberg D Menendez C Kahigwa E Aponte J Vidal J Tanner M Mshinda H Alonso P Intermittent treatment for malaria and anaemia control at time of routine vaccinations in Tanzanian infants a randomised placebo-controlled trial Lancet 20013571471ndash7

77 Schellenberg D Menendez C Aponte JJ Kahigwa E Tanner M Mshinda H Alonso P Intermittent preventive antimalarial treatment for Tanzanian infants follow-up to age 2 years of a randomised placebo-controlled trial Lancet 20053651481ndash3

78 OrsquoMeara WP Breman JG McKenzie FE The promise and potential challenges of intermittent preventive treat-ment for malaria in infants (IPTi) Malar J 2005433

79 White NJ Intermittent presumptive treatment for malaria PLoS Med 20052e3

80 Elagib AA Kider AO Akerstrom B Elbashir MI Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan Trans R Soc Trop Med Hyg 199892309ndash11

81 Minang JT Gyan BA Anchang JK Troye-Blomberg M Perlmann H Achidi EA Haptoglobin phenotypes and malaria infection in pregnant women at delivery in western Cameroon Acta Trop 200490107ndash14

82 Quaye IK Ekuban FA Goka BQ Adabayeri V Kurtzhals JA Gyan B Ankrah NA Hviid L Akanmori BD Hap-toglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria Trans R Soc Trop Med Hyg 200094216ndash9

83 Singh IP Walter H Bhasin MK Bhardwaj V Sudhakar K Genetic markers and malaria Observations in Gujarat India Hum Hered 19863631ndash6

84 Aucan C Walley AJ Greenwood BM Hill AV Hap-toglobin genotypes are not associated with resistance to severe malaria in The Gambia Trans R Soc Trop Med Hyg 200296327ndash8

85 Bienzle U Eggelte TA Adjei LA Dietz E Ehrhardt S Cramer JP Otchwemah RN Mockenhaupt FP Limited influence of haptoglobin genotypes on severe malaria in Ghanaian children Trop Med Int Health 200510668ndash71

86 Takeda M Kikuchi M Ubalee R Na-Bangchang K Ruangweerayut R Shibahara S Imai S Hirayama K Microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with susceptibility to cerebral malaria in Myanmar Jpn J Infect Dis 2005 58268ndash71

87 Shankar AH Nutritional modulation of malaria mor-bidity and mortality J Infect Dis 2000182 Suppl 1 S37ndash53

88 Gera T Sachdev HP Effect of iron supplementation on incidence of infectious illness in children systematic review Bmj 20023251142

Page 14: Iron metabolism and malaria

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S537Iron metabolism and malaria

RF Prevalence of iron deficiency with and without concurrent anemia in population groups with high prevalences of malaria and other infections a study in Cote drsquoIvoire Am J Clin Nutr 200174776ndash82

9 Allen SJ OrsquoDonnell A Alexander ND Alpers MP Peto TE Clegg JB Weatherall DJ alpha+-Thalassemia protects children against disease caused by other infec-tions as well as malaria Proc Natl Acad Sci U S A 1997 9414736ndash41

10 Murray MJ Murray AB Murray MB Murray CJ The adverse effect of iron repletion on the course of certain infections Br Med J 197821113ndash5

11 Smith AW Hendrickse RG Harrison C Hayes RJ Greenwood BM The effects on malaria of treatment of iron-deficiency anaemia with oral iron in Gambian children Ann Trop Paediatr 1989917ndash23

12 Oppenheimer SJ Gibson FD Macfarlane SB Moody JB Harrison C Spencer A Bunari O Iron supplementation increases prevalence and effects of malaria report on clinical studies in Papua New Guinea Trans R Soc Trop Med Hyg 198680603ndash12

13 Byles AB Drsquosa A Reduction of reaction due to iron dextran infusion using chloroquine Br Med J 19703625ndash7

14 Berger J Dyck JL Galan P Aplogan A Schneider D Traissac P Hercberg S Effect of daily iron supplementa-tion on iron status cell-mediated immunity and inci-dence of infections in 6ndash36 month old Togolese children Eur J Clin Nutr 20005429ndash35

15 Chippaux JP Schneider D Aplogan A Dyck JL Berger J [Effects of iron supplementation on malaria infection] Bull Soc Pathol Exot 19918454ndash62

16 Desai MR Mei JV Kariuki SK Wannemuehler KA Phil-lips-Howard PA Nahlen BL Kager PA Vulule JM ter Kuile FO Randomized controlled trial of daily iron sup-plementation and intermittent sulfadoxine-pyrimeth-amine for the treatment of mild childhood anemia in western Kenya J Infect Dis 2003187658ndash66

17 Nwanyanwu OC Ziba C Kazembe PN Gamadzi G Gandwe J Redd SC The effect of oral iron therapy during treatment for Plasmodium falciparum malaria with sulphadoxine-pyrimethamine on Malawian chil-dren under 5 years of age Ann Trop Med Parasitol 199690589ndash95

18 Verhoef H West CE Nzyuko SM de Vogel S van der Valk R Wanga MA Kuijsten A Veenemans J Kok FJ Intermittent administration of iron and sulfadoxine-py-rimethamine to control anaemia in Kenyan children a randomised controlled trial Lancet 2002360908ndash14

19 van den Hombergh J Dalderop E Smit Y Does iron therapy benefit children with severe malaria-associated anaemia A clinical trial with 12 weeks supplementation of oral iron in young children from the Turiani Division Tanzania J Trop Pediatr 199642220ndash7

20 Lawless JW Latham MC Stephenson LS Kinoti SN Pertet AM Iron supplementation improves appetite and growth in anemic Kenyan primary school children J Nutr 1994124645ndash54

21 Mebrahtu T Stoltzfus RJ Chwaya HM Jape JK Savioli L Montresor A Albonico M Tielsch JM Low-dose daily iron supplementation for 12 months does not increase the prevalence of malarial infection or den-sity of parasites in young Zanzibari children J Nutr 20041343037ndash41

22 Menendez C Kahigwa E Hirt R Vounatsou P Aponte JJ Font F Acosta CJ Schellenberg DM Galindo CM Kimario J Urassa H Brabin B Smith TA Kitua AY Tanner M Alonso PL Randomised placebo-controlled trial of iron supplementation and malaria chemoproph-ylaxis for prevention of severe anaemia and malaria in Tanzanian infants Lancet 1997350844ndash50

23 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S MrsquoBoge B Greenwood BM The effects of iron supplementation during pregnancy given by traditional birth attendants on the prevalence of anaemia and malaria Trans R Soc Trop Med Hyg 199488590ndash3

24 van Hensbroek MB Morris-Jones S Meisner S Jaffar S Bayo L Dackour R Phillips C Greenwood BM Iron but not folic acid combined with effective antimalarial therapy promotes haematological recovery in African children after acute falciparum malaria Trans R Soc Trop Med Hyg 199589672ndash6

25 Sazawal S Black RE Ramsan M Chwaya HM Stoltzfus RJ Dutta A Dhingra U Kabole I Deb S Othman MK Kabole FM Effects of routine prophylactic supplemen-tation with iron and folic acid on admission to hospital and mortality in preschool children in a high malaria transmission setting community-based randomised placebo-controlled trial Lancet 2006367133ndash43

26 Harvey PW Heywood PF Nesheim MC Galme K Zegans M Habicht JP Stephenson LS Radimer KL Brabin B Forsyth K et al The effect of iron therapy on malarial infection in Papua New Guinean schoolchil-dren Am J Trop Med Hyg 19894012ndash8

27 Andrews NC Iron homeostasis insights from genetics and animal models Nat Rev Genet 20001208ndash17

28 Kristiansen M Graversen JH Jacobsen C Sonne O Hoffman HJ Law SK Moestrup SK Identification of the haemoglobin scavenger receptor Nature 2001409 198ndash201

29 Wickramasinghe SN Abdalla SH Blood and bone marrow changes in malaria Baillieres Best Pract Res Clin Haematol 200013277ndash99

30 Phillips RE Looareesuwan S Warrell DA Lee SH Karbwang J Warrell MJ White NJ Swasdichai C Weatherall DJ The importance of anaemia in cerebral and uncomplicated falciparum malaria role of compli-cations dyserythropoiesis and iron sequestration Q J Med 198658305ndash23

31 Abdalla S Weatherall DJ Wickramasinghe SN Hughes M The anaemia of P falciparum malaria Br J Haematol 198046171ndash83

32 Sen R Bhatnagar BM Singh U Yadav MS Sehgal PK Patterns of erythropoiesis and anaemia in malaria J Commun Dis 199022247ndash53

33 Srichaikul T Wasanasomsithi M Poshyachinda V Panikbutr N Rabieb T Ferrokinetic studies and eryth-ropoiesis in malaria Arch Intern Med 1969124623ndash8

34 Das BS Thurnham DI Das DB Influence of malaria on markers of iron status in children implications for interpreting iron status in malaria-endemic communi-ties Br J Nutr 199778751ndash60

35 Menendez C Quinto LL Kahigwa E Alvarez L Fern-andez R Gimenez N Schellenberg D Aponte JJ Tanner M Alonso PL Effect of malaria on soluble transferrin receptor levels in Tanzanian infants Am J Trop Med Hyg 200165138ndash42

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S538 A M Prentice et al

36 Stoltzfus RJ Chwaya HM Montresor A Albonico M Savioli L Tielsch JM Malaria hookworms and recent fever are related to anemia and iron status indicators in 0- to 5-y old Zanzibari children and these relationships change with age J Nutr 20001301724ndash33

37 Stoltzfus RJ Chwaya HM Albonico M Schulze KJ Savioli L Tielsch JM Serum ferritin erythrocyte pro-toporphyrin and hemoglobin are valid indicators of iron status of school children in a malaria-holoendemic population J Nutr 1997127293ndash8

38 Massaga JJ Kitua AY Lemnge MM Akida JA Malle LN Ronn AM Theander TG Bygbjerg IC Effect of intermittent treatment with amodiaquine on anaemia and malarial fevers in infants in Tanzania a randomised placebo-controlled trial Lancet 20033611853ndash60

39 Verhoef H West CE Kraaijenhagen R Nzyuko SM King R Mbandi MM van Laatum S Hogervorst R Schep C Kok FJ Malarial anemia leads to adequately increased erythropoiesis in asymptomatic Kenyan children Blood 20021003489ndash94

40 Stoltzfus RJ Chway HM Montresor A Tielsch JM Jape JK Albonico M Savioli L Low dose daily iron supplementation improves iron status and appetite but not anemia whereas quarterly anthelminthic treatment improves growth appetite and anemia in Zanzibari preschool children J Nutr 2004134348ndash56

41 Kurtzhals JA Addae MM Akanmori BD Dunyo S Koram KA Appawu MA Nkrumah FK Hviid L Anae-mia caused by asymptomatic Plasmodium falciparum infection in semi-immune African schoolchildren Trans R Soc Trop Med Hyg 199993623ndash7

42 Loyevsky M John C Dickens B Hu V Miller JH Gordeuk VR Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators Mol Biochem Parasitol 199910143ndash59

43 Scholl PF Tripathi AK Sullivan DJ Bioavailable iron and heme metabolism in Plasmodium falciparum Curr Top Microbiol Immunol 2005295293ndash324

44 Darbari D Loyevsky M Gordeuk V Kark JA Castro O Rana S Apprey V Kurantsin-Mills J Fluorescence meas-urements of the labile iron pool of sickle erythrocytes Blood 2003102357ndash64

45 Ginsburg H Iron acquisition by Plasmodium spp Para-sitol Today 199915466

46 Atamna H Ginsburg H Heme degradation in the presence of glutathione A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells J Biol Chem 199527024876ndash83

47 Gabay T Ginsburg H Hemoglobin denaturation and iron release in acidified red blood cell lysatemdasha possible source of iron for intraerythrocytic malaria parasites Exp Parasitol 199377261ndash72

48 Iyer JK Shi L Shankar AH Sullivan DJ Jr Zinc pro-toporphyrin IX binds heme crystals to inhibit the proc-ess of crystallization in Plasmodium falciparum Mol Med 20039175ndash82

49 Cabantchik ZI Moody-Haupt S Gordeuk VR Iron che-lators as anti-infectives malaria as a paradigm FEMS Immunol Med Microbiol 199926289ndash98

50 Hershko C Control of disease by selective iron deple-tion a novel therapeutic strategy utilizing iron chelators Baillieres Clin Haematol 19947965ndash1000

51 Pradines B Tall A Ramiandrasoa F Spiegel A Sokhna C Fusai T Mosnier J Daries W Trape JF Kunesch G Parzy D Rogier C In vitro activity of iron-binding compounds against Senegalese isolates of Plasmodium falciparum J Antimicrob Chemother 2006571093ndash9

52 Meshnick SR Yang YZ Lima V Kuypers F Kam-chonwongpaisan S Yuthavong Y Iron-dependent free radical generation from the antimalarial agent artem-isinin (qinghaosu) Antimicrob Agents Chemother 1993371108ndash14

53 Golenser J Domb A Mordechai-Daniel T Leshem B Luty A Kremsner P Iron chelators correlation between effects on Plasmodium spp and immune functions J Parasitol 200692170ndash7

54 Nyakeriga AM Williams TN Marsh K Wambua S Perlmann H Perlmann P Grandien A Troye-Blomberg M Cytokine mRNA expression and iron status in chil-dren living in a malaria endemic area Scand J Immunol 200561370ndash5

55 Smith HJ Meremikwu M Iron chelating agents for treating malaria Cochrane Database Syst Rev 2003CD001474

56 Weatherall DJ The global problem of genetic disease Ann Hum Biol 200532117ndash22

57 Williams TN Maitland K Bennett S Ganczakowski M Peto TE Newbold CI Bowden DK Weatherall DJ Clegg JB High incidence of malaria in alpha-thalassaemic children Nature 1996383522ndash5

58 Rees DC Williams TN Maitland K Clegg JB Weather-all DJ Alpha thalassaemia is associated with increased soluble transferrin receptor levels Br J Haematol 1998103365ndash9

59 Maitland K Williams TN Bennett S Newbold CI Peto TE Viji J Timothy R Clegg JB Weatherall DJ Bowden DK The interaction between Plasmodium falciparum and P vivax in children on Espiritu Santo island Van-uatu Trans R Soc Trop Med Hyg 199690614ndash20

60 Weatherall DJ Clegg JB Genetic variability in response to infection malaria and after Genes Immun 2002 3331ndash7

61 Parikh S Dorsey G Rosenthal PJ Host polymorphisms and the incidence of malaria in Ugandan children Am J Trop Med Hyg 200471750ndash3

62 Destro Bisol G Genetic resistance to malaria oxidative stress and hemoglobin oxidation Parassitologia 1999 41203ndash4

63 Cappadoro M Giribaldi G OrsquoBrien E Turrini F Mannu F Ulliers D Simula G Luzzatto L Arese P Early phago-cytosis of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes parasitized by Plasmodium falciparum may explain malaria protection in G6PD deficiency Blood 1998922527ndash34

64 Arese P Turrini F Schwarzer E Band 3complement-mediated recognition and removal of normally senes-cent and pathological human erythrocytes Cell Physiol Biochem 200516133ndash46

65 Atkinson SH Rockett K Sirugo G Bejon PA Fulford A OrsquoConnell M A Bailey R Kwiatkowski DP Prentice AM Seasonal Childhood Anaemia in West Africa Is Associated with the Haptoglobin 2-2 Genotype PLoS Med 20063e172

66 Cabrera G Cot M Migot-Nabias F Kremsner PG Deloron P Luty AJ The sickle cell trait is associated

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S539Iron metabolism and malaria

with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens J Infect Dis 20051911631ndash8

67 Williams TN Mwangi TW Roberts DJ Alexander ND Weatherall DJ Wambua S Kortok M Snow RW Marsh K An immune basis for malaria protection by the sickle cell trait PLoS Med 20052e128

68 Ayi K Turrini F Piga A Arese P Enhanced phagocyto-sis of ring-parasitized mutant erythrocytes a common mechanism that may explain protection against falci-parum malaria in sickle trait and beta-thalassemia trait Blood 20041043364ndash71

69 Roberts DJ Harris T Williams T The influence of inherited traits on malaria infection In Bellamy R ed Susceptibility to infectious diseases the importance of host genetics Cambridge Cambridge University Press 2004 139ndash84

70 Williams TN Mwangi TW Wambua S Alexander ND Kortok M Snow RW Marsh K Sickle cell trait and the risk of Plasmodium falciparum malaria and other child-hood diseases J Infect Dis 2005192178ndash86

71 Aidoo M Terlouw DJ Kolczak MS McElroy PD ter Kuile FO Kariuki S Nahlen BL Lal AA Udhayakumar V Protective effects of the sickle cell gene against malaria morbidity and mortality Lancet 20023591311ndash2

72 Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K Nega-tive epistasis between the malaria-protective effects of alpha+-thalassemia and the sickle cell trait Nat Genet 2005371253ndash7

73 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S Ascaso C Smith T MrsquoBoge B Greenwood BM The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS Trans R Soc Trop Med Hyg 199589289ndash92

74 Terlouw DJ Desai MR Wannemuehler KA Kariuki SK Pfeiffer CM Kager PA Shi YP Ter Kuile FO Relation between the response to iron supplementation and sickle cell hemoglobin phenotype in preschool children in western Kenya Am J Clin Nutr 200479466ndash72

75 Duffy PE Fried M Malaria in the pregnant woman Curr Top Microbiol Immunol 2005295169ndash200

76 Schellenberg D Menendez C Kahigwa E Aponte J Vidal J Tanner M Mshinda H Alonso P Intermittent treatment for malaria and anaemia control at time of routine vaccinations in Tanzanian infants a randomised placebo-controlled trial Lancet 20013571471ndash7

77 Schellenberg D Menendez C Aponte JJ Kahigwa E Tanner M Mshinda H Alonso P Intermittent preventive antimalarial treatment for Tanzanian infants follow-up to age 2 years of a randomised placebo-controlled trial Lancet 20053651481ndash3

78 OrsquoMeara WP Breman JG McKenzie FE The promise and potential challenges of intermittent preventive treat-ment for malaria in infants (IPTi) Malar J 2005433

79 White NJ Intermittent presumptive treatment for malaria PLoS Med 20052e3

80 Elagib AA Kider AO Akerstrom B Elbashir MI Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan Trans R Soc Trop Med Hyg 199892309ndash11

81 Minang JT Gyan BA Anchang JK Troye-Blomberg M Perlmann H Achidi EA Haptoglobin phenotypes and malaria infection in pregnant women at delivery in western Cameroon Acta Trop 200490107ndash14

82 Quaye IK Ekuban FA Goka BQ Adabayeri V Kurtzhals JA Gyan B Ankrah NA Hviid L Akanmori BD Hap-toglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria Trans R Soc Trop Med Hyg 200094216ndash9

83 Singh IP Walter H Bhasin MK Bhardwaj V Sudhakar K Genetic markers and malaria Observations in Gujarat India Hum Hered 19863631ndash6

84 Aucan C Walley AJ Greenwood BM Hill AV Hap-toglobin genotypes are not associated with resistance to severe malaria in The Gambia Trans R Soc Trop Med Hyg 200296327ndash8

85 Bienzle U Eggelte TA Adjei LA Dietz E Ehrhardt S Cramer JP Otchwemah RN Mockenhaupt FP Limited influence of haptoglobin genotypes on severe malaria in Ghanaian children Trop Med Int Health 200510668ndash71

86 Takeda M Kikuchi M Ubalee R Na-Bangchang K Ruangweerayut R Shibahara S Imai S Hirayama K Microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with susceptibility to cerebral malaria in Myanmar Jpn J Infect Dis 2005 58268ndash71

87 Shankar AH Nutritional modulation of malaria mor-bidity and mortality J Infect Dis 2000182 Suppl 1 S37ndash53

88 Gera T Sachdev HP Effect of iron supplementation on incidence of infectious illness in children systematic review Bmj 20023251142

Page 15: Iron metabolism and malaria

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S538 A M Prentice et al

36 Stoltzfus RJ Chwaya HM Montresor A Albonico M Savioli L Tielsch JM Malaria hookworms and recent fever are related to anemia and iron status indicators in 0- to 5-y old Zanzibari children and these relationships change with age J Nutr 20001301724ndash33

37 Stoltzfus RJ Chwaya HM Albonico M Schulze KJ Savioli L Tielsch JM Serum ferritin erythrocyte pro-toporphyrin and hemoglobin are valid indicators of iron status of school children in a malaria-holoendemic population J Nutr 1997127293ndash8

38 Massaga JJ Kitua AY Lemnge MM Akida JA Malle LN Ronn AM Theander TG Bygbjerg IC Effect of intermittent treatment with amodiaquine on anaemia and malarial fevers in infants in Tanzania a randomised placebo-controlled trial Lancet 20033611853ndash60

39 Verhoef H West CE Kraaijenhagen R Nzyuko SM King R Mbandi MM van Laatum S Hogervorst R Schep C Kok FJ Malarial anemia leads to adequately increased erythropoiesis in asymptomatic Kenyan children Blood 20021003489ndash94

40 Stoltzfus RJ Chway HM Montresor A Tielsch JM Jape JK Albonico M Savioli L Low dose daily iron supplementation improves iron status and appetite but not anemia whereas quarterly anthelminthic treatment improves growth appetite and anemia in Zanzibari preschool children J Nutr 2004134348ndash56

41 Kurtzhals JA Addae MM Akanmori BD Dunyo S Koram KA Appawu MA Nkrumah FK Hviid L Anae-mia caused by asymptomatic Plasmodium falciparum infection in semi-immune African schoolchildren Trans R Soc Trop Med Hyg 199993623ndash7

42 Loyevsky M John C Dickens B Hu V Miller JH Gordeuk VR Chelation of iron within the erythrocytic Plasmodium falciparum parasite by iron chelators Mol Biochem Parasitol 199910143ndash59

43 Scholl PF Tripathi AK Sullivan DJ Bioavailable iron and heme metabolism in Plasmodium falciparum Curr Top Microbiol Immunol 2005295293ndash324

44 Darbari D Loyevsky M Gordeuk V Kark JA Castro O Rana S Apprey V Kurantsin-Mills J Fluorescence meas-urements of the labile iron pool of sickle erythrocytes Blood 2003102357ndash64

45 Ginsburg H Iron acquisition by Plasmodium spp Para-sitol Today 199915466

46 Atamna H Ginsburg H Heme degradation in the presence of glutathione A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells J Biol Chem 199527024876ndash83

47 Gabay T Ginsburg H Hemoglobin denaturation and iron release in acidified red blood cell lysatemdasha possible source of iron for intraerythrocytic malaria parasites Exp Parasitol 199377261ndash72

48 Iyer JK Shi L Shankar AH Sullivan DJ Jr Zinc pro-toporphyrin IX binds heme crystals to inhibit the proc-ess of crystallization in Plasmodium falciparum Mol Med 20039175ndash82

49 Cabantchik ZI Moody-Haupt S Gordeuk VR Iron che-lators as anti-infectives malaria as a paradigm FEMS Immunol Med Microbiol 199926289ndash98

50 Hershko C Control of disease by selective iron deple-tion a novel therapeutic strategy utilizing iron chelators Baillieres Clin Haematol 19947965ndash1000

51 Pradines B Tall A Ramiandrasoa F Spiegel A Sokhna C Fusai T Mosnier J Daries W Trape JF Kunesch G Parzy D Rogier C In vitro activity of iron-binding compounds against Senegalese isolates of Plasmodium falciparum J Antimicrob Chemother 2006571093ndash9

52 Meshnick SR Yang YZ Lima V Kuypers F Kam-chonwongpaisan S Yuthavong Y Iron-dependent free radical generation from the antimalarial agent artem-isinin (qinghaosu) Antimicrob Agents Chemother 1993371108ndash14

53 Golenser J Domb A Mordechai-Daniel T Leshem B Luty A Kremsner P Iron chelators correlation between effects on Plasmodium spp and immune functions J Parasitol 200692170ndash7

54 Nyakeriga AM Williams TN Marsh K Wambua S Perlmann H Perlmann P Grandien A Troye-Blomberg M Cytokine mRNA expression and iron status in chil-dren living in a malaria endemic area Scand J Immunol 200561370ndash5

55 Smith HJ Meremikwu M Iron chelating agents for treating malaria Cochrane Database Syst Rev 2003CD001474

56 Weatherall DJ The global problem of genetic disease Ann Hum Biol 200532117ndash22

57 Williams TN Maitland K Bennett S Ganczakowski M Peto TE Newbold CI Bowden DK Weatherall DJ Clegg JB High incidence of malaria in alpha-thalassaemic children Nature 1996383522ndash5

58 Rees DC Williams TN Maitland K Clegg JB Weather-all DJ Alpha thalassaemia is associated with increased soluble transferrin receptor levels Br J Haematol 1998103365ndash9

59 Maitland K Williams TN Bennett S Newbold CI Peto TE Viji J Timothy R Clegg JB Weatherall DJ Bowden DK The interaction between Plasmodium falciparum and P vivax in children on Espiritu Santo island Van-uatu Trans R Soc Trop Med Hyg 199690614ndash20

60 Weatherall DJ Clegg JB Genetic variability in response to infection malaria and after Genes Immun 2002 3331ndash7

61 Parikh S Dorsey G Rosenthal PJ Host polymorphisms and the incidence of malaria in Ugandan children Am J Trop Med Hyg 200471750ndash3

62 Destro Bisol G Genetic resistance to malaria oxidative stress and hemoglobin oxidation Parassitologia 1999 41203ndash4

63 Cappadoro M Giribaldi G OrsquoBrien E Turrini F Mannu F Ulliers D Simula G Luzzatto L Arese P Early phago-cytosis of glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes parasitized by Plasmodium falciparum may explain malaria protection in G6PD deficiency Blood 1998922527ndash34

64 Arese P Turrini F Schwarzer E Band 3complement-mediated recognition and removal of normally senes-cent and pathological human erythrocytes Cell Physiol Biochem 200516133ndash46

65 Atkinson SH Rockett K Sirugo G Bejon PA Fulford A OrsquoConnell M A Bailey R Kwiatkowski DP Prentice AM Seasonal Childhood Anaemia in West Africa Is Associated with the Haptoglobin 2-2 Genotype PLoS Med 20063e172

66 Cabrera G Cot M Migot-Nabias F Kremsner PG Deloron P Luty AJ The sickle cell trait is associated

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S539Iron metabolism and malaria

with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens J Infect Dis 20051911631ndash8

67 Williams TN Mwangi TW Roberts DJ Alexander ND Weatherall DJ Wambua S Kortok M Snow RW Marsh K An immune basis for malaria protection by the sickle cell trait PLoS Med 20052e128

68 Ayi K Turrini F Piga A Arese P Enhanced phagocyto-sis of ring-parasitized mutant erythrocytes a common mechanism that may explain protection against falci-parum malaria in sickle trait and beta-thalassemia trait Blood 20041043364ndash71

69 Roberts DJ Harris T Williams T The influence of inherited traits on malaria infection In Bellamy R ed Susceptibility to infectious diseases the importance of host genetics Cambridge Cambridge University Press 2004 139ndash84

70 Williams TN Mwangi TW Wambua S Alexander ND Kortok M Snow RW Marsh K Sickle cell trait and the risk of Plasmodium falciparum malaria and other child-hood diseases J Infect Dis 2005192178ndash86

71 Aidoo M Terlouw DJ Kolczak MS McElroy PD ter Kuile FO Kariuki S Nahlen BL Lal AA Udhayakumar V Protective effects of the sickle cell gene against malaria morbidity and mortality Lancet 20023591311ndash2

72 Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K Nega-tive epistasis between the malaria-protective effects of alpha+-thalassemia and the sickle cell trait Nat Genet 2005371253ndash7

73 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S Ascaso C Smith T MrsquoBoge B Greenwood BM The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS Trans R Soc Trop Med Hyg 199589289ndash92

74 Terlouw DJ Desai MR Wannemuehler KA Kariuki SK Pfeiffer CM Kager PA Shi YP Ter Kuile FO Relation between the response to iron supplementation and sickle cell hemoglobin phenotype in preschool children in western Kenya Am J Clin Nutr 200479466ndash72

75 Duffy PE Fried M Malaria in the pregnant woman Curr Top Microbiol Immunol 2005295169ndash200

76 Schellenberg D Menendez C Kahigwa E Aponte J Vidal J Tanner M Mshinda H Alonso P Intermittent treatment for malaria and anaemia control at time of routine vaccinations in Tanzanian infants a randomised placebo-controlled trial Lancet 20013571471ndash7

77 Schellenberg D Menendez C Aponte JJ Kahigwa E Tanner M Mshinda H Alonso P Intermittent preventive antimalarial treatment for Tanzanian infants follow-up to age 2 years of a randomised placebo-controlled trial Lancet 20053651481ndash3

78 OrsquoMeara WP Breman JG McKenzie FE The promise and potential challenges of intermittent preventive treat-ment for malaria in infants (IPTi) Malar J 2005433

79 White NJ Intermittent presumptive treatment for malaria PLoS Med 20052e3

80 Elagib AA Kider AO Akerstrom B Elbashir MI Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan Trans R Soc Trop Med Hyg 199892309ndash11

81 Minang JT Gyan BA Anchang JK Troye-Blomberg M Perlmann H Achidi EA Haptoglobin phenotypes and malaria infection in pregnant women at delivery in western Cameroon Acta Trop 200490107ndash14

82 Quaye IK Ekuban FA Goka BQ Adabayeri V Kurtzhals JA Gyan B Ankrah NA Hviid L Akanmori BD Hap-toglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria Trans R Soc Trop Med Hyg 200094216ndash9

83 Singh IP Walter H Bhasin MK Bhardwaj V Sudhakar K Genetic markers and malaria Observations in Gujarat India Hum Hered 19863631ndash6

84 Aucan C Walley AJ Greenwood BM Hill AV Hap-toglobin genotypes are not associated with resistance to severe malaria in The Gambia Trans R Soc Trop Med Hyg 200296327ndash8

85 Bienzle U Eggelte TA Adjei LA Dietz E Ehrhardt S Cramer JP Otchwemah RN Mockenhaupt FP Limited influence of haptoglobin genotypes on severe malaria in Ghanaian children Trop Med Int Health 200510668ndash71

86 Takeda M Kikuchi M Ubalee R Na-Bangchang K Ruangweerayut R Shibahara S Imai S Hirayama K Microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with susceptibility to cerebral malaria in Myanmar Jpn J Infect Dis 2005 58268ndash71

87 Shankar AH Nutritional modulation of malaria mor-bidity and mortality J Infect Dis 2000182 Suppl 1 S37ndash53

88 Gera T Sachdev HP Effect of iron supplementation on incidence of infectious illness in children systematic review Bmj 20023251142

Page 16: Iron metabolism and malaria

Delivered by Publishing Technology to Guest User IP 41217203183 on Fri 07 Nov 2014 133451Copyright (c) Nevin Scrimshaw International Nutrition Foundation All rights reserved

S539Iron metabolism and malaria

with enhanced immunoglobulin G antibody responses to Plasmodium falciparum variant surface antigens J Infect Dis 20051911631ndash8

67 Williams TN Mwangi TW Roberts DJ Alexander ND Weatherall DJ Wambua S Kortok M Snow RW Marsh K An immune basis for malaria protection by the sickle cell trait PLoS Med 20052e128

68 Ayi K Turrini F Piga A Arese P Enhanced phagocyto-sis of ring-parasitized mutant erythrocytes a common mechanism that may explain protection against falci-parum malaria in sickle trait and beta-thalassemia trait Blood 20041043364ndash71

69 Roberts DJ Harris T Williams T The influence of inherited traits on malaria infection In Bellamy R ed Susceptibility to infectious diseases the importance of host genetics Cambridge Cambridge University Press 2004 139ndash84

70 Williams TN Mwangi TW Wambua S Alexander ND Kortok M Snow RW Marsh K Sickle cell trait and the risk of Plasmodium falciparum malaria and other child-hood diseases J Infect Dis 2005192178ndash86

71 Aidoo M Terlouw DJ Kolczak MS McElroy PD ter Kuile FO Kariuki S Nahlen BL Lal AA Udhayakumar V Protective effects of the sickle cell gene against malaria morbidity and mortality Lancet 20023591311ndash2

72 Williams TN Mwangi TW Wambua S Peto TE Weatherall DJ Gupta S Recker M Penman BS Uyoga S Macharia A Mwacharo JK Snow RW Marsh K Nega-tive epistasis between the malaria-protective effects of alpha+-thalassemia and the sickle cell trait Nat Genet 2005371253ndash7

73 Menendez C Todd J Alonso PL Francis N Lulat S Ceesay S Ascaso C Smith T MrsquoBoge B Greenwood BM The response to iron supplementation of pregnant women with the haemoglobin genotype AA or AS Trans R Soc Trop Med Hyg 199589289ndash92

74 Terlouw DJ Desai MR Wannemuehler KA Kariuki SK Pfeiffer CM Kager PA Shi YP Ter Kuile FO Relation between the response to iron supplementation and sickle cell hemoglobin phenotype in preschool children in western Kenya Am J Clin Nutr 200479466ndash72

75 Duffy PE Fried M Malaria in the pregnant woman Curr Top Microbiol Immunol 2005295169ndash200

76 Schellenberg D Menendez C Kahigwa E Aponte J Vidal J Tanner M Mshinda H Alonso P Intermittent treatment for malaria and anaemia control at time of routine vaccinations in Tanzanian infants a randomised placebo-controlled trial Lancet 20013571471ndash7

77 Schellenberg D Menendez C Aponte JJ Kahigwa E Tanner M Mshinda H Alonso P Intermittent preventive antimalarial treatment for Tanzanian infants follow-up to age 2 years of a randomised placebo-controlled trial Lancet 20053651481ndash3

78 OrsquoMeara WP Breman JG McKenzie FE The promise and potential challenges of intermittent preventive treat-ment for malaria in infants (IPTi) Malar J 2005433

79 White NJ Intermittent presumptive treatment for malaria PLoS Med 20052e3

80 Elagib AA Kider AO Akerstrom B Elbashir MI Association of the haptoglobin phenotype (1-1) with falciparum malaria in Sudan Trans R Soc Trop Med Hyg 199892309ndash11

81 Minang JT Gyan BA Anchang JK Troye-Blomberg M Perlmann H Achidi EA Haptoglobin phenotypes and malaria infection in pregnant women at delivery in western Cameroon Acta Trop 200490107ndash14

82 Quaye IK Ekuban FA Goka BQ Adabayeri V Kurtzhals JA Gyan B Ankrah NA Hviid L Akanmori BD Hap-toglobin 1-1 is associated with susceptibility to severe Plasmodium falciparum malaria Trans R Soc Trop Med Hyg 200094216ndash9

83 Singh IP Walter H Bhasin MK Bhardwaj V Sudhakar K Genetic markers and malaria Observations in Gujarat India Hum Hered 19863631ndash6

84 Aucan C Walley AJ Greenwood BM Hill AV Hap-toglobin genotypes are not associated with resistance to severe malaria in The Gambia Trans R Soc Trop Med Hyg 200296327ndash8

85 Bienzle U Eggelte TA Adjei LA Dietz E Ehrhardt S Cramer JP Otchwemah RN Mockenhaupt FP Limited influence of haptoglobin genotypes on severe malaria in Ghanaian children Trop Med Int Health 200510668ndash71

86 Takeda M Kikuchi M Ubalee R Na-Bangchang K Ruangweerayut R Shibahara S Imai S Hirayama K Microsatellite polymorphism in the heme oxygenase-1 gene promoter is associated with susceptibility to cerebral malaria in Myanmar Jpn J Infect Dis 2005 58268ndash71

87 Shankar AH Nutritional modulation of malaria mor-bidity and mortality J Infect Dis 2000182 Suppl 1 S37ndash53

88 Gera T Sachdev HP Effect of iron supplementation on incidence of infectious illness in children systematic review Bmj 20023251142


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