Cis-regulatory CYP6P9b P450 variants associated with loss of insecticide-treated bed net efficacy against Anopheles funestus

Abstract

Elucidating the genetic basis of metabolic resistance to insecticides in malaria vectors is crucial to prolonging the effectiveness of insecticide-based control tools including long lasting insecticidal nets (LLINs). Here, we show that cis-regulatory variants of the cytochrome P450 gene, CYP6P9b, are associated with pyrethroid resistance in the African malaria vector Anopheles funestus. A DNA-based assay is designed to track this resistance that occurs near fixation in southern Africa but not in West/Central Africa. Applying this assay we demonstrate, using semi-field experimental huts, that CYP6P9b-mediated resistance associates with reduced effectiveness of LLINs. Furthermore, we establish that CYP6P9b combines with another P450, CYP6P9a, to additively exacerbate the reduced efficacy of insecticide-treated nets. Double homozygote resistant mosquitoes (RR/RR) significantly survive exposure to insecticide-treated nets and successfully blood feed more than other genotypes. This study provides tools to track and assess the impact of multi-gene driven metabolic resistance to pyrethroids, helping improve resistance management.

An Experimental Hut Evaluation of PBO-Based and Pyrethroid-Only Nets against the Malaria Vector Anopheles funestus Reveals a Loss of Bed Nets Efficacy Associated with GSTe2 Metabolic Resistance

“…funestus and the L119F-GSTe2 mutation as mosquitoes with the 119F resistance allele have significantly higher blood feeding rate compared to those with L119 susceptible allele against Olyset Net (p < 0.001) and Olyset plus (p < 0.001). This is similar with observations for the cytochrome P450s CYP6P9a and CYP6P9b for which the resistant alleles CYP6P9a_R and CYP6P9b_R were recently shown, in a release-recapture experimental hut study, to also provide a greater ability to blood feed and to survive exposure to pyrethroid-only LLIN (PermaNet 2.0) [14,34]. This suggests that L119F-GSTe2 mutation likely contributes to an increased malaria transmission as every additional bite increases the chance of sporozoite to be passed to the populations.…”

CYP6P9-Driven Signatures of Selective Sweep of Metabolic Resistance to Pyrethroids in the Malaria Vector Anopheles funestus Reveal Contemporary Barriers to Gene Flow

“…An. funestus mosquito populations from Mozambique and Malawi have previously been reported to share similar genetic differentiation patterns [16,18,19,[39][40][41]. Our data show the resistance allele is fixed in southern Africa, and further highlights its expansion to Tanzania in eastern Africa where gene flow was not observed between Uganda and Tanzania.…”

“…The selection of this CYP6P9a has been shown to be metabolically more efficient in metabolising pyrethroids [50], which may explain why pyrethroid resistance has been continuously associated with a high overexpression of CYP6P9a and CYP6P9b genes in multiple An. funestus populations from southern Africa [16,19,39,40,45]. However, the expression levels of key P450s such as CYP6P9a and CYP6P9b varies between populations suggesting that independent selection events for resistance to pyrethroids has occurred [41].…”

An Africa-wide genomic evolution of insecticide resistance in the malaria vector Anopheles funestus involves selective sweeps, copy number variations, gene conversion and transposons

“…funestus is also shown through the distribution of recently detected markers of insecticide resistance in this species with resistance alleles for RDL (resistance to dieldrin) [20] and for the glutathione-S transferase epsilon 2 (L119F-GSTe2) [21] only found in West/Central and part of East Africa but completely absent from southern Africa. In contrast, resistance alleles for the cytochrome P450 genes CYP6P9a_R [6] and CYP6P9b_R [22] as well as for the N485I Ace-1 conferring carbamate resistance [23] are all found only in southern Africa and part of East Africa but completely absent from other regions. In this, it is similar to Anopheles gambiae, which also shows a broad division between "eastern" and "north-western" African populations and an otherwise shallow population structure [24].…”