Comparison of the knockdown resistance locus (kdr) inAnopheles stephensi,An. arabiensis, andCulex pipiens s.l.suggests differing mechanisms of pyrethroid resistance in east Ethiopia

Abstract

27The recent detection of the malaria vector mosquito species Anopheles stephensi, which 28 is typically restricted to South Asia and the Middle East, in the Horn of Africa emphasizes the 29 importance of continued vector surveillance in the region. Previous reports of the absence of the 30 knockdown resistance mutations (kdr) in the voltage-gated sodium channel (vgsc) in pyrethroid 31 resistant An. stephensi emphasize the need for further investigation of the kdr-mediated 32 resistance mutations in other mosquitoes of east Ethiopia. In this study, the knockdown resistance 33 locus (kdr) in the voltage gated sodium channel (vgsc) was analyzed in An. stephensi, An. 34 arabiensis, and Culex pipiens s. l. collected in east Ethiopia between 2016 and 2017. A portion of 35 both vsgc was sequenced and amplified in An. arabiensis and Cu. pipiens s.l. and compared with 36 An. stephensi sequences previously generated. All of Cu. pipiens s.l. (n = 42) and 71.6% of the 37 An. arabiensis (n=67) carried kdr L1014F alleles known to confer pyrethroid resistance. Analysis 38 of the downstream kdr intron in all three species revealed nucleotide diversity only in An. 39 stephensi (s = 6, h = 3) previously shown to have no 1014 mutations. In addition, no evidence of 40 non-neutral evolutionary processes was detected for An. stephensi kdr intron. Finally, no 41 association between the An. stephensi kdr intron haplotypes and permethrin or DDT phenotypic 42 resistance was detected. Overall, these results reveal evidence for differing degrees of selection 43 at kdr that may suggest differing mechanisms of resistance across these species. While the 44 presence of the L1014F mutation suggests target-site resistance mechanisms in An. arabiensis 45 and Cu. pipiens in east Ethiopia, the lack of signatures for selection at kdr for resistant and non-46 resistant An. stephensi does not support a target-site mechanism of resistance based on the kdr 47 locus in An. stephensi. This evidence of differing mechanisms of resistance across vector species 48 can inform the design of future integrated strategies for vector control. 49 Synopsis 51 Growing insecticide resistance hinders efforts to control the spread of vector-borne diseases. This 52 is further complicated with the evidence of vectors moving into new regions as is the case with 53 the newly detected Anopheles stephensi in the Horn of Africa. With this dynamic situation, it is 54 important to evaluate how different local vectors develop resistance to insecticides to improve the 55 implementation of insecticide-based strategies meant to target multiple vectors species. The 56 authors analyzed a known insecticide resistance locus, kdr, in the An. stephensi and long-57 established An. arabiensis and Culex pipiens sl populations in east Ethiopia for evolutionary 58 signatures of the common mechanism of resistance known as knockdown (target-site) resistance. 59 The authors show that while An. arabiensis and Culex pipiens sl carry evolutionary signatures of 60 the knockdown resistance mechanism, ...

Tracking of Anopheles stephensi in Ethiopia using mitochondrial DNA reveals pattern of spread

“…stephensi. Also, there is evidence of diverse insecticide resistance mechanisms among species of Anopheles [16][17][18] . Given these differences, vector control approaches are in the process of being modified to account for the presence of An.…”