Insecticide resistance and social practices relating to pesticide use by populations in Africa: how to provide pertinent information to control Anopheles gambiae s.s., the main malaria vector in West Africa – AlterNET

(1) An anthropology study to describe and analyse the representations and practices of human populations in the use of insecticides in a social context will be conducted in Benin and Burkina Faso; it will include inventory of products, perception of benefits and risks attributed to the different products, perception of nuisance, etc. An analysis of the decision processes in the choice of products and practices will be made.
(2) A genetic characterization of OP and CX insecticide resistance will be conducted in distinct ecological areas. It will give information on the distribution and evolution of the frequency of the resistance genes to perform a global analysis. In parallel, a phenotypic characterization will be conducted by measuring fitness and behaviour of laboratory resistant strains in controlled conditions.
(3) Models to estimate selection parameters and migration to predict future dynamics of OP/CX resistance alleles in Anopheles gambiae s.s. will be developed.

The relationships between health and environment have often been underestimated in Africa. Urbanization increases and impact of humans on environment is likely to promote the emergence of diseases. The development of vegetable growing within cities may constitute an explosive «cocktail« in terms of vector proliferation, pesticides pollution and selection of resistance. The AlterNET project will help to better apprehend how these recent environmental changes may influence the dynamic of malaria.

A strong originality of this project is that we will evaluate the possibility of using new insecticides before resistance does fail the control programs. We will also identify the origin(s) of insecticide pressures to have a global understanding of insecticide uses in specific societal contexts.

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Malaria is one of the deadliest diseases transmitted by Anopheles gambiae in West Africa. As no vaccine is yet available and no direct control of breeding sites possible, the main option to control malaria is to prevent vector-host contact. This is mainly achieved by using insecticide-treated bed-nets (ITNs) and indoor residual house spraying. Presently the only recommended insecticides for treating mosquito nets are pyrethroids (PYRs) because of their excito-repellent properties, efficacy at low-dose, and good tolerance in humans. However, the extensive and rapid roll out of ITNs in the last decade selected PYR resistance in A. gambiae from the whole sub-Saharan Africa. This constitutes a major hindrance to malaria control.
The goal of the AlterNET project is to acquire pertinent information concerning the risk of using insecticides from two other insecticide classes (organophosphates [OPs] and carbamates [CXs]), which have been proposed to work around PYR resistance. As the dynamics of resistance is driven by the biological and population characteristics of the considered species and by the intensity of the selection pressure it receives, the project is organized along two main axes:
1. Understand OP and CX selection pressures.
As no global health control program uses OP or CX for mosquito control in Africa, the question is open to clearly identify the origin of selection pressures that have selected the ace-1 alleles presently observed in A. gambiae. These pressures probably result from environmental pollutions generated by human activities that require insect control such as agriculture and/or domestic personal protection. They need to be clarified, both in terms of insecticide usages (quantity, frequency) and locations.
To identify OP and CX pressures from all origins in distinct ecological areas, we will:
(a) investigate the professional practices of market gardeners, especially concerning the uses of pesticides, using the concepts and tools developed for "Pharmaceutical anthropology". A precise knowledge of the nature and quantity of pesticides, apprehending the socio-cultural building of decision processes in the choice and practices of insecticide uses will be acquired;
(b) monitor resistance of Culex pipiens quinquefasciatus, a mosquito species adapted to a wide range of habitats with a particularly fast response to selection pressure. Data will feed previously developed models for estimating selection pressure.
2. Study the adaptation to OP and CX of A. gambiae populations.
Some A. gambiae s.s. populations from West Africa have already developed resistance to OP and CX by selection of a single mutation in the ace-1 gene (ace-1R) coding the synaptic acetylcholinesterase (AChE1). Recently, a new "duplicated" allele, ace-1D, putting in tandem a wild-type and a resistant copy of ace-1 on the same chromosome was detected in Ivory Coast and Burkina Faso. This duplication is suspected to improve mosquito fitness while maintaining resistance and could favour resistance spread.
We will monitor the distribution of ace-1R and ace-1D alleles in Benin and Burkina Faso, from 2013 to 2015. We will also generate and analyze lab strains carrying these resistance alleles in a similar genetic background to evaluate their impact on mosquito fitness (including behaviour). Population models will be developed and parameterized with the data acquired from field surveys and strain analyses to monitor and predict OP/CX resistance dynamics.
The combination of the different investigations concerning An. gambiae and selection pressures along with anthropological data will bring about information about how OP and CX resistance could evolve, may or may not jeopardize malaria control, and possibly could be modified, the ultimate goal of the AlterNET project.