A cytochrome P450 allele confers pyrethroid resistance on a major African malaria vector, reducing insecticide-treated bednet efficacy

Abstract

Metabolic resistance to insecticides such as pyrethroids in mosquito vectors threatens control of malaria in Africa. Unless it is managed, recent gains in reducing malaria transmission could be lost. To improve monitoring and assess the impact of insecticide resistance on malaria control interventions, we elucidated the molecular basis of pyrethroid resistance in the major African malaria vector, Anopheles funestus. We showed that a single cytochrome P450 allele (CYP6P9a_R) in A. funestus reduced the efficacy of insecticide-treated bednets for preventing transmission of malaria in southern Africa. Expression of key insecticide resistance genes was detected in populations of this mosquito vector throughout Africa but varied according to the region. Signatures of selection and adaptive evolutionary traits including structural polymorphisms and cis-regulatory transcription factor binding sites were detected with evidence of selection due to the scale-up of insecticide-treated bednet use. A cis-regulatory polymorphism driving the overexpression of the major resistance gene CYP6P9a allowed us to design a DNA-based assay for cytochrome P450–mediated resistance to pyrethroid insecticides. Using this assay, we tracked the spread of pyrethroid resistance and found that it was almost fixed in mosquitoes from southern Africa but was absent from mosquitoes collected elsewhere in Africa. Furthermore, a field study in experimental huts in Cameroon demonstrated that mosquitoes carrying the resistance CYP6P9a_R allele survived and succeeded in blood feeding more often than did mosquitoes that lacked this allele. Our findings highlight the need to introduce a new generation of insecticide-treated bednets for malaria control that do not rely on pyrethroid insecticides.

Climate change and the genetics of insecticide resistance

“…In some cases, coding changes in these genes can also increase their enzymatic activity, resulting in higher rates of insecticide metabolism . Alleles that confer target‐site and metabolic resistance usually have elevated frequencies in populations under the selective pressure of continuous insecticide usage …”

“…21 Alleles that confer target-site and metabolic resistance usually have elevated frequencies in populations under the selective pressure of continuous insecticide usage. 16,22…”

Influence of genetic polymorphism on transcriptional enhancer activity in the malaria vector Anopheles coluzzii

“…Numerous Gal4 based enhancer trapping lines exist for Anopheles stephensi largely as a tool for the study mosquito functional genomics and optimizing methods to drive transgene expression 28 . Recent work in the African malaria vector Anopheles funestus, highlights the profound effects of indel variation at a cis regulatory element in the enhancer/promoter region of a cytochrome P450 and its association with insecticide resistance 29 . Thus, relatively simple evolved sequence variation in enhancers can produce large phenotypic shifts in the organism 30, 31 .…”

Influence of GST- and P450-based metabolic resistance to pyrethroids on blood feeding in the major African malaria vectorAnopheles funestus

“…funestus . This marker used to show that mosquitoes carrying this P45O-resistant allele survived and succeeded in blood feeding more often than did susceptible mosquitoes when exposed to insecticide-treated nets [24]. The design of assays for both GST- and P45O-based resistance now offers a great opportunity to explore how the blood feeding process is impacted by metabolic resistance mechanism in malaria vectors and further assess how resistance may impact the vectorial capacity of mosquitoes to transmit malaria in the field.…”

“…Here, we assessed the effect of metabolic resistance to pyrethroids on the blood feeding process in An. funestus , using the two DNA-based metabolic resistance markers: L119F-GSTe2 and CYP6P9a -R [22,24]. Specifically, we assessed the association between the genotypes of these metabolic resistance markers and key parameters of blood feeding including mosquito probing time, feeding duration and the bloodmeal size revealing a contrasting impact.…”