The G119S Acetylcholinesterase (Ace-1) Target Site Mutation Confers Carbamate Resistance in the Major Malaria Vector Anopheles gambiae from Cameroon: A Challenge for the Coming IRS Implementation

Growing resistance is reported to carbamate insecticides in malaria vectors in Cameroon. However, the contribution of acetylcholinesterase (Ace-1) to this resistance remains uncharacterised. Here, we established that the Ace-1R mutation is driving resistance to carbamates in Anopheles gambiae populations from Cameroon. Insecticide bioassay on field collected mosquitoes from Bankeng, a locality in southern Cameroon, showed high resistance to the carbamates bendiocarb (64.8 ± 3.5 % mortality) and propoxur (55.71 ± 2.9 %) but a full susceptibility to the organophosphate fenithrothion. The TaqMan genotyping of the Ace-1R mutation with field-collected adults revealed the presence of this resistance allele (39%). A significant correlation was observed between the Ace-1R and carbamate resistance at allelic [(bendiocarb; OR = 75.9; P<0.0001) and (propoxur; OR= 1514; P<0.0001)] and genotypic [RR vs SS (bendiocarb; OR = 120.8; P<0.0001) and (propoxur; OR= 3277; P<0.0001) levels. Furthermore, the presence of the mutation was confirmed by sequencing an Ace-1 portion flanking codon 119. The cloning of this fragment revealed a likely duplication of Ace-1 in Cameroon as mosquitoes exhibited at least three distinct haplotypes. Phylogenetic analyses showed that the predominant Ace-1R allele is identical to that from West Africa suggesting a recent introduction of this allele in Central Africa from the West. The spread of this Ace-1R represents a serious challenge to future implementation of IRS-based interventions using carbamates or organophosphates in Cameroon.