Abstract
The spread of resistance to insecticides in disease-carrying mosquitoes poses a threat to the effectiveness of control programmes, which rely largely on insecticide-based interventions. Monitoring mosquito populations is essential, but obtaining phenotypic measurements of resistance is laborious and error-prone. High-throughput genotyping offers the prospect of quick and repeatable estimates of resistance, while also allowing resistance markers to be tracked and studied. To demonstrate the potential of highly-mulitplexed genotypic screening for measuring resistance-association of mutations and tracking their spread, we developed a panel of 28 known or putative resistance markers in the major malaria vector Anopheles gambiae, which we used to screen mosquitoes from a wide swathe of Sub-Saharan Africa (Burkina Faso, Ghana, Democratic Republic of Congo (DRC) and Kenya). We found resistance association in four markers, including a novel mutation in the detoxification gene Gste2 (Gste2-119V). We also identified a duplication in Gste2 combining a resistance-associated mutation with its wild-type counterpart, potentially alleviating the costs of resistance. Finally, we describe the distribution of the multiple origins of kdr resistance, finding unprecedented diversity in the DRC. This panel represents the first step towards a quantitative genotypic model of insecticide resistance that can be used to predict resistance status in An. gambiae.
Highlights
It is estimated that the use of insecticide-treated nets and indoor residual spraying of insecticide has been responsible for 78% of 663 million cases of malaria averted in the period 2000–20151
Our aim is to develop a highly-multiplexed genotypic panel that can be used in the first instance to quantify the insecticide-resistance association of mutations, and in the second instance to track these mutations across mosquito populations
Of the 8,036 individual assays performed on samples from Ag1000G (287 samples × 28 single nucleotide polymorphism (SNP)), only 5 (0.06%) iPLEX calls were divergent from the Ag1000G callset
Summary
It is estimated that the use of insecticide-treated nets and indoor residual spraying of insecticide has been responsible for 78% of 663 million cases of malaria averted in the period 2000–20151. To maintain effective malaria control, accurate assessment of the insecticide resistance profile of mosquito populations is essential. Phenotypic assessment of insecticide resistance requires live mosquitoes of fixed age to be assayed in carefully controlled conditions. Phenotyping approaches are only sensitive when resistance has reached appreciable frequency in the population For these reasons, there is great interest in the prospect of screening mosquitoes for the genetic signatures of insecticide. By understanding where resistance originates, research can begin to elucidate the environmental and population-level contexts which favour its rise and spread. This has been seen in the evolution of drug resistance in the malaria parasite, which repeatedly appears and spreads from an area in Cambodia[7], driving research into understanding the causes of this pattern. A substantial proportion of the variance in resistance remains unexplained, making it crucial to identify new markers and to quantify their impact
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