Lab study finds permethrin-resistant Kenyan mosquitoes remain competent for dengue-2

A laboratory study of Aedes aegypti mosquitoes collected from three selected sites in Kenya’s Lamu County found that permethrin-resistant subpopulations at Hindi and Mokowe remained capable of becoming infected with dengue-2 virus and developing disseminated infections. Mosquitoes from Shela were susceptible to permethrin, while samples from all three sites showed evidence of dengue-2 infection and dissemination after infectious blood meals.

Researchers collected Ae. aegypti mosquitoes from Shela, Hindi and Mokowe using traps and assessed permethrin susceptibility through World Health Organization insecticide-resistance assays. Mortality in the Shela population exceeded 98%, indicating susceptibility. By contrast, mortality was 47% in Hindi and 37.6% in Mokowe, leading the investigators to classify those populations as resistant. These results document a geographic contrast among the sampled sites rather than a change over time across Lamu County.

To test vectorial competence, second-generation mosquitoes were exposed to blood meals containing infectious dengue-2 virus. Fully engorged mosquitoes were then incubated for up to 21 days and tested by plaque assay for infection and dissemination. Among mosquitoes examined from Hindi, 14 of 60, or 23%, had midgut infections, while 12 of 60, or 20%, had disseminated infections. In Mokowe, 24 of 90 mosquitoes, or 27%, had midgut infections and 11 of 90, or 12%, had disseminated infections. At Shela, 40 of 130 mosquitoes, or 31%, had midgut infections and 21 of 130, or 16%, had disseminated infections. Shela therefore had the highest observed proportion of midgut infection, while Hindi had the highest proportion of disseminated infection. The measured proportions did not show that permethrin resistance prevented competence, but the study does not establish whether the mosquitoes would transmit dengue-2 to people at the same rates in the field.

The investigators separately examined genetic variation in 31 female mosquitoes by extracting genomic DNA from their legs, amplifying a mitochondrial DNA target with the HCO2198 and LCO1490 primers, and analyzing the amplicons through Sanger sequencing. All samples were identified as members of the Ae. aegypti formosus sub-species. Haplotype diversity was 1.0, while nucleotide diversity was 0.01184, indicating the presence of many haplotypes alongside comparatively low nucleotide-level variation. Together, the findings show that the selected Lamu County populations differed in permethrin susceptibility while retaining genetic characteristics consistent with Ae. aegypti formosus. Because the study covered three sites and assessed dengue-2 competence under laboratory conditions, its results should not be generalized to every mosquito population or to human dengue transmission in the county.

Subject of Research: Permethrin resistance, genetic diversity and dengue-2 vector competence of Aedes aegypti mosquitoes in Lamu County, Kenya

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

Article References: Qureish, K. S., Mulwa, F., Odinga, R., Yalwala, S., Lutomiah, J., Bargul, J. L., Kellar, G. G., Eads, J., & Eyase, F. (2026). Vector competence for dengue-2 virus of permethrin resistant/ susceptible Aedes aegypti sub-populations from selected sites in Lamu County, Kenya. PLOS One, 21(10), e0359810. https://doi.org/10.1371/journal.pone.0359810

Image Credits: AI Generated

DOI: 10.1371/journal.pone.0359810

Keywords: Aedes aegypti, dengue-2 virus, vector competence, permethrin resistance, insecticide susceptibility, viral dissemination, mitochondrial DNA, Lamu County, Kenya, Vector, competence, dengue-2