Genetic variability and vector competence ofAedes aegyptipopulations from Kisumu and Busia Counties, Western Kenya, for Chikungunya and Zika viruses
Authors: Anyango Victor O. , Langat Solomon , Mulwa Francis , Mutisya James , Koka Hellen , Okoyo Collins , Chepkorir Edith , Konongoi Samson , Karanja Anncarol , Kerubo Glennah , Sang Rosemary , Lutomiah Joel 
Published: July 2023

Aedes aegyptiis the primary vector of several arboviruses, including dengue virus (DENV), chikungunya virus (CHIKV), yellow fever virus (YFV), and Zika virus (ZIKV). This vector is widespread globally in tropical and subtropical areas, but also found in temperate areas. Kenya experienced its first chikungunya outbreaks in Lamu County in 2004 and later in Mandera: 2016, and Mombasa: 2017. While there is yet to be a report of Zika outbreaks in Kenya, sero-surveillance studies indicate low-level transmission of this virus in coastal and northern parts of the country. Despite the presence ofAe. aegyptiin Kisumu and Busia counties in sufficient densities, and free movement of people between the coast and the two western Kenya counties, no outbreaks of either disease have been reported in these regions. To investigate this phenomenon, we collectedAe. aegyptimosquitoes from county headquarter towns near railway stations connecting the coast and western Kenya and reared them under controlled laboratory conditions. The mosquitoes were then assessed for genetic variability using CO1 genes as well as their efficiency to transmit viruses using Laboratory colonies (F1) of the field mosquitoes challenged with an infectious blood meal containing CHIKV and ZIKV.

Genetic analysis revealed the presence of bothAe. aegyptisubspecies, (Ae. aegypti aegypti[Aaa] andAe. aegypti formosus[Aaf]) in the two western Kenya counties, withAafbeing dominant (19:8 for Kisumu samples and 25:6 for Busia samples). Additionally, pairwise comparison revealed minimal genetic differentiation (0.62%) between the study populations, with a high genetic variation (99.38%) observed within each population, indicating significant diversity within individual populations.Ae. aegyptipopulations from Kisumu and Busia counties exhibited competence for CHIKV, with infection, dissemination, and transmission rates of 55.2%, 85.5%, and 27.1% for Kisumu; and 57.8%, 71.8%, and 25% for Busia populations, respectively. There was no significant difference in vector competence between these two populations. Interestingly, neither population was competent for ZIKV. In conclusion, the data shows that theAe. aegyptipopulations in the two cities were homogeneous. This could explain the observed similarity in vector competence for CHIKV and ZIKV.

Author Summary

Our study investigated the genetic variability and vector competence ofAe. aegyptimosquito populations in Kisumu and Busia Counties to CHIKV and ZIKV; revealing the presence and even distribution of bothAaaandAafsubspecies. We also found that theAe. aegyptipopulations from the two counties were not genetically differentiated. Furthermore, our study revealed that theAe. aegyptimosquitoes from Kisumu and Busia counties were competent for CHIKV but may be refractory to ZIKV infection. These findings highlight the importance of continued monitoring ofAe. aegyptipopulations and their potential for arboviral disease transmission in the region.