Abstract:
Kenya has experienced outbreaks of chikungunya in the recent past with the most recent occurring in Mandera in the northern region in May 2016 and in Mombasa in the coastal region from November 2017 to Febuary 2018. Despite the reported outbreaks in Kenya, vector competence studies have only been conducted on Aedes aegypti mosquitoes; however the role played by other mosquito species in transmission and maintenance of the chikungunya virus in endemic areas remains unclear. This study sought to determine vector competence of rural Ae. bromeliae and Ae. vittatus mosquitoes in the transmission of chikungunya virus, focusing on Kilifi and West Pokot regions of Kenya.This is a laboratory based experimental study that involves oral infection of mosquitoes with infectious blood meal and observing the outcome of the infection. Four day old female mosquitoes were fed orally on chikungunya virus-infected blood at a dilution ration of 1:1(106.4 plaque-forming units [PFU]/ml) using artificial membrane feeder (hemotek system) for 45 minutes. The engorged mosquitoes were picked and incubated at 29-30°C ambient temperature and 70-80% relative humidity in the insectary. At 5, 7 and 10 days post infection the mosquitoes were selected and carefully dissected to separate the legs and wings from the body and their proboscises individually inserted in the capillary tube containing minimum essential media (MEM) to collect salivary expectorate. The resulting homogenates and the salivary expectorates were tested by plaque assay to determine virus infection, dissemination and transmission potential of the mosquitoes. A total of 515 female mosquitoes (311 Ae. bromeliae and 204 Ae. vittatus) were exposed to the East, central and Southern Africa (ECSA) lineage of chikungunya virus. Ae. vittatus showed high susceptibility to the virus ranging from 75-90% and moderate dissemination and transmission rates ranging from 35-50%. Ae. bromeliae had moderate susceptibility ranging from 26-40% and moderate dissemination and transmission rates ranging from 27-55%. Findings from this study showed that strains of Ae. vittatus and Ae. bromeliae populations from West Pokot Kenya and Kilifi county respectively were competent vectors for CHIKV. Overall, about 70% of the Ae. vittatus and about 40% of the Ae. bromeliae that ingested >10 6.4 plaque-forming units of virus/mL became infected and about 30% of the virus-exposed mosquitoes transmitted virus to a capillary tube. Vector competence remains a prerequisite in risk assessment, surveillance and control of vector.. This study shows that both Ae. vittatus and Ae. bromeliae populations from West Pokot and Kilifi counties of Kenya are competent vectors of chikungunya virus. Based on these results, the two areas are at risk of virus transmission and outbreaks in the event of virus introduction. Therefore, this study underscores the need to institute vector competence studies for different populations of potential vector species across the country as a means of evaluating risk of transmission of the emerging and re-emerging arboviruses in diverse regions of Kenya.
