Application of New Approaches to Measuring Intensity of Insecticide Resistance: Results and Implications

Moussa BM CISSE, Dereje DENGELA, Bradford LUCAS, Jules MIHIGO, Aboubacar SADOU, Allison BELEMVIRE, Kristen GEORGE, Christen FORNADEL, Laura NORRIS, Suzanne POWELL, Bill BROGDON and Raymond BEACH.

ASTMH 64th Annual Meeting October 25-29, 2015

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WHO standard tube test provides important information on the spread and frequency of resistance but not on the strength or intensity of resistance.

Recent study results by Bagi and colleagues, 2015 underlined the importance of measuring the strength or intensity of resistance to predict the likelihood of operational impact of resistance on malaria control.

Background

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LLINs are the primary method of vector control in Mali followed by IRS.

Insecticide resistance (IR) data collected from 13 sites using WHO standard tube test in 2012 indicated widespread and high frequency resistance of local vector to pyrethroid (PY) (Cisse et al. 2015).

However, the vector killing effect of LLINs depends on the performance of insecticide used to treat the nets, which is PY.

Insecticide resistance intensity study in Mali

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The impact of the high frequency of PY resistance observed in Mali on the efficacy of LLINs is unknown.

Evidence from PMI work in Zambia indicates that strength or intensity of resistance is associated with operational failure.

To help gain information on the strength of the PY resistance observed, quantitative data was collected using modified CDC bottle bioassay.

Insecticide resistance intensity study in Mali

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Assess resistance of An. gambiae s.l. to pyrethroids.

Assess intensity of PY resistance in the field population of An. gambiae s.l.

Identify mechanism responsible for PY resistance

Interpret possible impact of PY resistance on vector control activities.

Objectives

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MethodFigure 1: Eco-Climate map of Mali with resistance surveillance sites

13 sites were selected in southern and central Mali

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Larval collectionLarvae and pupae were collected from July to December 2014 in each surveillance site and reared to adults. 3-5 day female non-bloodfed adults were used for each bioassay.

Susceptibility assessment 20-25 female adult mosquitoes were exposed 1h, to WHO tube with insecticide impregnated papers -permethrin 0.75% and deltamethrin 0.05% (PY) in four replicates. The test mortality rates were recorded after 24h (WHO, 2013).

Method

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Resistance intensity assessment20-25 female adult mosquitoes were exposed for 2h to CDC bottle coated with the following doses of permethrin and deltamethrin in four replicates. The test mortality rates were recorded at the diagnostic time of 30 minutes.

Method

Insecticide Insecticide concentration

(µg/bottle)

Permethrin 1X 21.5

Permethrin 2 X 43

Permethrin 5X 107.5

Permethrin 10X 215

Deltamethrin 1X 12.5

Deltamethrin 2X 25

Deltamethrin 5X 62.5

Deltamethrin

10X 125

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Results

Figure 2: WHO insecticide susceptibility test results by site.

Kita

Koulik

oro

Kati

Bamak

o CIV Bla

Barao

ueli

Niono

Selin

gue

Bougo

uni

Kadio

lo

Djenn

e

Bandi

gara

Banka

ss0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00permethrin 0.75% Deltamethrin 0.05%

% M

ort

ality

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ResultsFigure 3: CDC Permethrin resistance intensity by site

 

Kita

Koulik

oro

Kati

Bamak

o CIV Bla

Barou

eli

Niono

Selin

gue

Bougo

uni

Kadio

lo

Djenn

e

Bandi

gara

Banka

ss0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

1X

% M

ort

ality

Kita

Koulik

oro

Kati

Bamak

o CIV Bla

Barou

eli

Niono

Selin

gue

Bougo

uni

Kadio

lo

Djenn

e

Bandi

gara

Banka

ss0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

2X

% M

ort

ality

Kita

Koulik

oro

Kati

Bamak

o CIV Bla

Barou

eli

Niono

Selin

gue

Bougo

uni

Kadio

lo

Djenn

e

Bandi

gara

Banka

ss0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

5X

% M

ort

ality

Kita

Koulik

oro

Kati

Bamak

o CIV Bla

Barou

eli

Niono

Selin

gue

Bougo

uni

Kadio

lo

Djenn

e

Bandi

gara

Banka

ss0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

10X%

Mota

lity

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ResultsFigure 4: CDC Deltamethrin resistance intensity by site

 

Kita

Koulik

oro

Kati

Bamak

o CIV Bla

Barou

eli

Niono

Selin

gue

Bougo

uni

Kadio

lo

Djenn

e

Bandi

gara

Banka

ss0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

1X

% M

ort

ality

Kita

Koulik

oro

Kati

Bamak

o CIV Bla

Barou

eli

Niono

Selin

gue

Bougo

uni

Kadio

lo

Djenn

e

Bandi

gara

Banka

ss0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

2X

% M

ort

ality

Kita

Koulik

oro

Kati

Bamak

o CIV Bla

Barou

eli

Niono

Selin

gue

Bougo

uni

Kadio

lo

Djenn

e

Bandi

gara

Banka

ss0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

5X

% M

ort

ality

Kita

Koulik

oro

Kati

Bamak

o CIV Bla

Barou

eli

Niono

Selin

gue

Bougo

uni

Kadio

lo

Djenn

e

Bandi

gara

Banka

ss0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

10X

% M

ort

ality

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Results

The allelic frequency of kdr ranged from 50% to 100% in An. coluzzii, 50% to 94% in An. gambiae s.s., and 20% to 100% in An. arabiensis.

Kis

um

u

Nio

no

Bla

Bara

oueli

Dje

nné

Bankas

Bandia

gara

Bam

ako C

IV

Kit

a

Baguin

eda

Koulikoro

Sélingué

Bougounie

Kadio

lo

0.000

0.050

0.100

0.150

0.200

0.250

0.300

nm

ol P

450/m

g p

rote

ine

Figure 5: Mixed Function Oxidases

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Discussion

An. gambiae s.l. tested from surveillance sites was strongly resistant to permethrin and deltamethrin.

An. gambiae s.l. exposed to permethrin at 10 times the diagnostic dosage showed 19% - 95% mortality in all 13 sites. An. gambiae s.l. exposed to this diagnostic dosage (10X) of deltamethrin showed 33% - 93% survivorship in 11 of the sites.

High intensity of PY resistance can be explained by the widespread kdr mutation and strength of metabolic resistance.

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PY resistance is being caused by a combination of elevated MFOs and kdr, and maybe other mechanisms as well. Heterogeneity between insecticides and in sites near each other.

Intensity of resistance was higher to permethrin than to deltamethrin in 9 sites and higher for deltamethrin than permethrin in 2 sites.

Presence of high intensity of PY resistance in An. gambiae s.l. may present an obstacle to the future success of malaria control based on ITNs. There is a need to routinely monitor IR to develop a vector resistance management plan.

Conclusion

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Impact of new combination LLIN products on entomological measures of malaria transmission in Mali

Performance of two combination LLINs in reducing indoor resting density, longevity, and infection rates of An. gambiae s.l. in areas of pyrethroid resistance associated with MFO mechanism, compared with the performance of two conventional analogues.

Impact of each of the 4 LLIN products on frequency of pyrethroid resistance phenotypes over time.

Compare net loss associated with fabric integrity between all 4 types of LLIN products under study.

Next Step?

Thank you!