Vector competence for dengue-2 virus of permethrin resistant/ susceptible Aedes aegypti sub-populations from selected sites in Lamu County, Kenya

Abstract

Dengue virus, primarily transmitted by Aedes aegypti mosquitoes, is endemic in Lamu County. There is currently no definitive treatment for dengue; therefore, vector control remains the most effective method to curb transmission. Prolonged exposure of Ae. aegypti to insecticides may confer resistance. This study aimed to determine the levels of resistance to permethrin, a commonly used insecticide, and to compare the vectorial competence and genetic differences of resistant versus susceptible populations for dengue-2 virus. Ae. aegypti mosquitoes were collected from Lamu (Shela, Hindi, and Mokowe) using traps and assayed for permethrin resistance/ susceptibility. WHO insecticide resistance assays were conducted. The mosquitoes (F2) were exposed to dengue-2 infectious bloodmeals and fully engorged mosquitoes selected, incubated for up to 21 days, and tested for infection and dissemination by plaque assay. Individual legs were dissected from 31 female (F0) mosquitoes for isolation of genomic DNA. Polymerase Chain Reaction was used to amplify the target mitochondrial DNA using HCO2198 and LCO1490 primers. The amplicons were Sanger sequenced to determine genetic diversity. The Shela sub-population displayed susceptibility (>98% mortality), whereas the Hindi and Mokowe sub-populations exhibited resistance, with mortality rates of 47% and 37.6%, respectively. Of the mosquitoes from Hindi (n = 60); Mokowe (n = 90); and Shela (n = 130), n = 14 (23%), n = 24 (27%), and n = 40 (31%) respectively, had midgut infections with dengue-2; while n = 12 (20%), n = 11 (12%), and n = 21 (16%) respectively had disseminated infection. Genetic analysis showed that all the samples were Ae. aegypti formosus sub-species. Haplotype diversity was high at 1.0 while nucleotide diversity was low at 0.01184. These findings suggest Ae. aegypti formosus sub-species is prevalent in Lamu County. The study also demonstrated high infection and dissemination rates among the Ae. aegypti sub- populations.