Techniques for mitigating aflatoxin-producing fungi

www.iita.org A member of CGIAR consortium

Juliet Akello

Techniques for mitigating aflatoxin-producing fungi

The Silent Killer: Aflatoxins


About IITA

IITA

Aflatoxin:

What they are

Drivers

Status in sub-Saharan Africa

Interventions

Future research prospects


About IITA

International research organization

founded in 1967

Develop sustainable food production

systems in tropical Africa

Most important African link in

CGIAR

198 scientists and > 2,000 staff

Operate throughout sub-Saharan

Africa

Research along entire value chain

Lusaka


Highly toxic metabolite produced by

the fungus Aspergillus section Flavi

Common & widespread fungus in soil

& decaying matter

Fungus is sometimes visible, toxin is

not

Aspergillus

What is Aflatoxin?

Aflatoxin


Types of aflatoxin

Aflatoxin

13 different types of aflatoxin are produced in nature

Most common: aflatoxins B1, B2, G1 & G2

Aflatoxin B1 is the most toxic.

Aflatoxin M1:

• breakdown product of Aflatoxin B1

• excreted in the urine & milk of exposed humans/

animals.

Aflatoxin contamination: causative agent

A. flavus L- strain A. flavus S- strain A. parasiticus

+++++

- / +

Aflatoxin-producing Aspergillus spp

Aflatoxin contamination: causative agent

Reverse

Front

A. oryzae A. sojae A. tamarii

8

Colony & Microscopic Characteristics

Rough conidia

Smooth conidia

A. parasiticus

A. flavus


Aspergillus Spp. & Aflatoxins

Ability to produce aflatoxins in A. flavus strains varies

Some strains produce a lot (toxigenic) & others little or no aflatoxins

(atoxigenic)

Species/strain B aflatoxin G aflatoxin

A. flavus ‘L-strains’ +/- -

A. flavus ‘S-strains’ + -

A. flavus ‘SBG strains’ + +

A. parasiticus + +

A. nomius + +

A. tamarii - -

Maize

SUCEPTIBLE CROPS: MANY

Cassava

Cashew nut Groundnut


Aflatoxin contamination: when does it occur?

Phase 1: Before crop maturity

a. Developing crop becomes infected

b. Linked to crop damage (pests,

stress)

Phase 2: After crop maturity

a. Aflatoxin increases with crop

maturity

b. May occur before or after

harvest

c. Seed is vulnerable till consumed

Occurs in 2 phases

SYMPTOMS OF FUNGAL CONTAMINATION

Infected maize cobs

Maize

Clean maize


Clean groundnut Infected groundnut


Contaminated cassava

Clean cassava


a) Susceptible crops b) Favorable climate

Infection before crop maturity: plant stress (high T, drought)

Aflatoxin problem in SSA: drivers


Aflatoxin contamination: monitoring

Monitoring starts in the field

• diseased plant parts

• Sampling


Aflatoxin contamination: monitoring

Monitoring continues in the lab

• Black light (UV light-365nm)-

for greenish gold fluorescence

• Commercial test kits


Aflatoxin prevalence in foods & feeds in SSA

• Several African staple commodities affected

• High human exposure in Africa – mother to baby

• Levels and frequency of occurrence high

– >30% maize in stores with >20 ppb aflatoxin

– ~90% stores are contaminated with Afla fungi

– Up to 40% grain in households with aflatoxin


Aflatoxin prevalence in foods & feeds in SSA

• Several African staple commodities affected

• High human exposure in Africa – mother to baby

• Levels and frequency of occurrence high

– >30% maize in stores with >20 ppb aflatoxin

– ~90% stores are contaminated with Afla fungi

– Up to 40% grain in households with aflatoxin

AFLATOXIN IN ZAMBIA

0

20

40

60

80

100

2011/2012 2013/2014

To

xig

en

ic s

tra

ins (

%)

Atoxigenic

Toxigenic

Aflatoxin producing fungus (Aspergillus) in Zambian soils

fungus colonizing groundnut root zones in soils


Year Maize Groundnut Reference

1979 - 5 Kannaiyan et al. 1979

1998 900-929 6200-8600 Njapau et al. 1998

2009 0.7-108.4 - Kankolongo et al. 2009

2010 10 - Mukanga et al. 2010

2012/2013 0-255 0-5350 IITA-unpublished

Aflatoxin levels (ppb) detected in maize & groundnut samples from different

parts of Zambia

Surveillance studies

Aflatoxin levels depended on: locality, crop, processing method &

presence of microbial contaminants

FACTORS PROMOTING CONTAMINATION

a) Late planting and harvest


b) Poor drying techniques


c) Poor storage and informal marketing systems

d) Lack of awareness & inadequate regulatory systems

Aflatoxin problem in SSA: drivers


d) Favorable climate (High temperatures and drought/

dry periods) and insect pests

35°N

35°S

HARMFUL EFFECTS OF AFLATOXIN

Taiwan

1967

Uganda

1970

Western India

1974

Kenya

1982

2002

2004

2005

2006

2007

2008

Malaysia

1988

35°N

35°S

Causes death: history of Acute Outbreaks


Causes poisoning and death: Acute toxicity in humans are rare, but deaths have been reported

40 deaths in 1974 (India); 13 deaths in 1990 in Malaysia

14 deaths in 2001 (Kenya); > 200 deaths in 2010 (Kenya)


• Enhances stunting and underweight in children


• Causes liver rot, enlarged liver, and liver cancer

• Enhances susceptibility to illnesses

• Suppresses the immune system


Up to 3.4 increment in Feed conversion ratio

Livestock and poultry losses

losses in feed efficiency

Recurrent infection due to losses in feed efficiency

Bird mortality


40% reduction in live weight

500 ppb AF diet AF-free diet


reduced growth rate

AF-free diet



decreased milk & egg yield

embryo toxicity (reduced

reproductivity)

death (cattle, turkey, swine..)

Carry over: high levels

Meat, eggs, Gizzards, Diary products, Kidneys & cheese


Aflatoxin, a threat to trade! Serious Trade Barrier (Market exclusion)

~2.3 M bags untradeable Many SSA unable to sell

<4 <10 <20 <10

EU WFP US COMESA

Acceptable Limits (ppb)

>20

unsafe

CODEX Alimetarius Commission

Regulatory standard: 20 ppb

REDUCING AFLATOXIN CONTAMINATION

1. Awareness, advocacy & training

Early harvest, proper drying and storage



Maintain crop hygiene at all levels: sorting/ physical

separation, and destruction of contaminated grains


Use of mechanical groundnut sheller instead of wetting

BIOLOGICAL CONTROL OF AFLATOXIN

AflaSafe biopesticide

Mixture of 4 atoxigenic

strains of A. flavus of local

origin


At application: Maize

Broadcast aflasafe by hand 2 to 3 weeks before flowering by

broadcasting at a rate of 10 kg/ha


At application: Groundnut

Apply aflasafe between 30 to 40 days after planting by side

dressing along the rows on the soil surface (rate of 10 kg/ha).


Aflatoxin mitigation: what can be done?

Detection systems

Management options

Afla-ELISATM, AcuScan flow readers

Africa-wide surveillance fungal populations, climate change, predictive modeling

Plant breeding resistant maize/ groundnut lines

AflasafeTM

Mycotoxin assessment

research pathway example of research

Technology adoption

Capacity building

Science

Techniques for mitigating aflatoxin-producing fungi