Fixation of Voltage Gated Sodium Channel Mutation 995F in Pyrethroid Resistant Anopheles Gambiae S.S Populations and Widespread Occurrence of Vgsc Mutations and Copy Number Variants in Anopheles Coluzzii Mosquitoes from Southern Côte D’Ivoire

Resistance to pyrethroid and organophosphate insecticides in the malaria vector Anopheles gambiae s.l. has been shown to be conferred by a variety of mechanisms. Knowledge of the distribution of resistant mosquito populations is a prerequisite for establishing better strategies for their management. In this study, a total of 755 Anopheles gambiae s.l from Southern Côte d’Ivoire were exposed to deltamethrin or pirimiphos-methyl insecticides and were screened to assess the distribution of mutations known or believed to confer resistance to both insecticides. Most individuals from the An. gambiae s.l complex were identified by molecular tests as An. coluzzii. Survival to deltamethrin (from 94% to 97%) was higher than to pirimiphos-methyl (from 10% to 49%). In An. gambiae s.s, the mutation in the Voltage Gated Sodium Channel (VGSC) at the 995F locus (Vgsc-995F) was fixed with other target site mutations very rare (Vgsc-402L: 0%; Vgsc-1570Y:0%, Acetylcholinesterase Acel-280S: 14%). In An. coluzzii species, the Vgsc-995F mutation was found at higher frequency of 65% followed by other target site mutations (Vgsc-402L: 35%; Vgsc-1570Y: 1%; Acel-280S: 45%). The Vgsc-995S mutation was not present. The presence of the Ace1-280S mutation was found to be significantly linked to the presence of the Ace1 copy number variant (CNV): Ace1_AgDup. The Cyp6aa / Cyp6p CNVs Dup 7 (20%) and Dup 14 (24%) were the most frequent. The Ace1 CNV Ace1_AgDup, and five CNVs in the Cyp6aa / Cyp6p gene cluster were detected in An. coluzzii, while Ace1_AgDup, the deletion Ace1_Del97 and two Cyp6aa / Cyp6p- CNVs were found in An. gambiae s.s. Elevated expression of Cyp6p3 was associated with deltamethrin resistance, although there was no association of resistance with copy number in this gene. Studies should include screening for a new variant 402 to effectively monitor An. coluzzii resistance. Use of alternative insecticides and control methods to arrest resistance spread in An. coluzzii population is merited.