Unbiased sequence analysis of vgsc gene reveals circulation of novel and known knock-down resistance mutations in Culex pipiens, challenging vector control measures

Pyrethroids, targeting the voltage gated sodium channel (VGSC), are fundamental for the control of arboviral disease circulation. The spread of pyrethroid resistance among vector species represents thus a major public health concern. Culex pipiens is one of the most abundant European mosquito species and main vector of West Nile virus, leading cause of arboviral encephalitis worldwide. Despite this, monitoring of its resistance status and the understanding of underlying mechanisms are widely neglected. Herein, we performed an oligo-hybridization capture approach on 82 Cx. pipiens specimens from Italy and Greece to investigate the whole coding sequence of the vgsc gene for the presence of known and potential knock-down resistance (kdr) mutations associated with target-site resistance to pyrethroids in insects. Among the 26 non-synonymous substitutions revealed by the analysis, the super-kdr haplotype—i.e. the association of kdr-alleles 918T and 1014F, known for conferring a strongly enhanced resistance phenotype in Musca domestica – was revealed for the first time in mosquitoes. Three more potential kdr alleles were detected for the first time in Cx. pipiens and multiple kdr variants were observed for locus 1014, with allele 1014F, reaching frequencies  > 80%. Overall, results depict a worrisome situation that could affect the ability to control West Nile virus outbreaks in southern Europe. To avoid this, resistance monitoring needs to be intensified and an enhancement of the diagnostic tool box for the easy detection of different kdr-variants (including in particular the super-kdr haplotype) and for subsequent functional studies on the resistance phenotype of detected variants, is required