Vector Competence for Dengue-2 Virus and Genetic Diversity of Permethrin Resistant/ Susceptible Aedes Aegypti Sub-populations From Lamu County, Kenya

Background Dengue virus, primarily transmitted by Aedes aegypti mosquitoes, is endemic in Lamu County with the most recent outbreak in 2021. 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. Methods Ae. aegypti mosquito eggs were collected from Lamu (Shela, Hindi, and Mokowe) using ovitraps and hatched in the insectary. The emerging adults were assayed for permethrin resistance/ susceptibility. WHO insecticide resistance assays (n = 145) were conducted utilizing 3,525 emerged mosquitoes; 1,575 each from Hindi and Mokowe, and 375 from Shela. The mosquitoes (F ₂ ) 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. Proportion test of differences was used to determine significant differences between sub-populations and incubation periods at 0.05 level of significance. Individual legs were dissected from 31 female (F ₀ ) 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. Results The Shela sub-population displayed lower resistance (1%) compared to the Hindi and Mokowe sub-populations at 53% and 62.4% 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 0.989 while nucleotide diversity was low at 0.01184. Conclusion These findings suggest that 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. This confirms the risk of DENV-2 transmission and highlights the need for regular entomological surveillance for early detection of virus and initiation of preventive strategies such as vector control.