Genome-wide population genetics and molecular surveillance of insecticide resistance in Anopheles stephensi mosquitoes from Ethiopia

Abstract

Since the detection of the Asian mosquito Anopheles stephensi in Dijbouti in 2012, it has spread throughout the Horn of Africa. This invasive vector has continued moving across the continent and is a threat to malaria control programs. Vector control methods including insecticide-treated nets and indoor residual spraying, have substantially reduced the malaria burden. However, the increasing prevalence of mosquitos resistant to insecticides, including An. stephensi populations, threaten reductions made so far. Here, we generate whole genome sequencing data for An. stephensi sourced from an Ethiopian town (n=27) and compare South Asian populations (n=45; India and Pakistan), assessing genomic diversity, population structure, and uncovering insecticide resistance mutations. Population structure analysis using genome-wide single nucleotide polymorphisms (n=15,533,476), revealed Ethiopian isolates clustering as a distinct ancestral group, separate to South Asian isolates. Three insecticide resistance-associated SNPs (gaba gene: A296S and V327I; vgscL1014F) were detected. Evidence of ongoing selection was found in several loci, including genes previously associated with neonicotinoids, ivermectin, DDT, and pyrethroid resistance. This study represents the first genome-wide population genetics study of invasive An. stephensi, revealing genomic differences from South Asian populations, which can be used for future assessments of vector population dispersal and detection of insecticide resistance mechanisms.