Dengue virus serotype 4 in Aedes aegypti mosquitoes in Kenya.

Dengue fever is one of the most globally significant arthropod-borne viral diseases. In 2024, more than 14 million cases and 10,000 deaths were reported across 92 tropical and subtropical countries. Dengue virus (DENV), endemic in Sub-Saharan Africa including Kenya, comprises four serotypes (DENV-1 to DENV-4). While DENV-1 to DENV-3 are widely distributed in the region, DENV-4 is considered rare. However, information on the distribution of DENV serotypes and the genetic diversity within African mosquito populations remains limited. To address this gap, 2,400 Aedes aegypti, the primary vector species of DENV, were collected from southeastern and coastal Kenya between 2016 and 2019 and subjected to viral analyses. Collected samples were screened for orthoflaviviruses using a nested pan-orthoflavi RT-PCR, and positive samples were Sanger sequenced. DENV-4 genotype I was detected in a pool of two female Ae. aegypti collected during a dengue outbreak in Mombasa in 2017, which was predominantly associated with DENV-2. The DENV-4 genome retrieved from this strain was similar to sequences of DENV-4 that have previously been reported from South India. We report the detection and genomic characterization of DENV-4 genotype I in Kenyan mosquito populations. These findings contribute to current knowledge of DENV serotype distribution in southeastern Africa and highlight the need for improved genomic surveillance to guide effective dengue prevention and control strategies.