Vector Competence of a Coastal Population of Aedes aegypti for Dengue 2 and 3 Virus Serotypes in Kenya

Abstract

Aedes aegypti is the primary vector of dengue, an arboviral disease caused by dengue virus (DENV) that exists as four distinct serotypes (DENV 1-4). While all four DENV serotypes circulate in Kenya, differential distribution of the serotypes in specific regions suggests virus transmission may differ among local vector populations. In this study, we tested the hypothesis that a coastal Ae. aegypti population (Rabai, Kilifi County) varies in its ability to transmit DENV-2 (predominant) and DENV-3 (less dominant) and that transmission is related to Ae. aegypti subspecies—domestic Ae. aegypti aegypti (Aaa) and sylvtic Ae. aegypti formosus (Aaf). We orally exposed F1 females (3-10 days old) to blood meals containing DENV-2 (10 5.30 pfu/ml) or DENV-3 (10 5.13 pfu/ml), tested them individually for infection (body), dissemination (legs), and transmission (saliva) at 7, 14, and 21 days postinfection (DPI), respectively, and compared the rates between the serotypes. We analyzed cytochrome c oxidase I gene (cox-I) sequences among DENV-susceptible and non-susceptible cohorts. Of 489 mosquitoes tested (DENV-2: 240; DENV-3: 249), we found consistently higher but nonsignificant rates of infection (16% vs. 10%), dissemination (47% (18/38) vs. 35% (9/26)), and transmission (39% (7/18) vs. 11% (1/9) for DENV-2 than DENV-3. However, DENV-2 exhibited a shorter extrinsic incubation period (EIP) for disseminated infection (7-DPI vs. 14-DPI) and transmission (14-DPI vs. 21-DPI) compared to DENV-3. Two cox-I lineages were recovered in phylogeny, one predominantly clustered with referenced Aaa and a minor lineage grouped with Aaf. Infected mosquitoes and those with disseminated infection were represented in both lineages; those that transmitted the viruses grouped with the Aaa-associated lineage only. We conclude that the coastal Ae. aegypti population is a competent vector for DENV-2 and DENV-3 likely driven by the domestic Aaa that is predominant. The shorter EIP to attain dissemination and transmission for DENV-2 could favour its transmission over DENV-3.