The Effect of Rearing Temperature on the Vector Competence of Ae. aegypti Mosquito Populations from Kilifi and Nairobi Counties for Dengue-2 Virus

Abstract

Susceptibility of Ae. aegypti mosquito to dengue virus (DENV) varies geographically and can be influenced by climatic factors such as temperature, which affect the incidence, seasonality and distribution of vector-borne diseases. The first outbreak of dengue fever (DF) in Kenya occured in 1982 in the coastal towns of Malindi and Kilifi. Unlike Nairobi where no active dengue transmission has been reported, DF is currently re-emerging at the Coast causing major outbreaks. This study investigated the effect of rearing temperature on the vector competence of Ae. aegypti populations from Kilifi and Nairobi counties for dengue-2 virus. A total of 1,117 four-day old adult female Ae. aegypti mosquitoes collected as eggs from the two sites were artificially exposed to defibrinated sheep blood mixed with dengue-2 virus (105.08 PFU/ml) using a membrane feeder. Half of the exposed mosquitoes were incubated at high temperature (30°C) and the other half at low temperature (26°C), and every 7 days up to day 21 post-infection 30% of the exposed mosquitoes were randomly picked, individually dissected, separated into abdomen and legs, and tested for midgut and disseminated infection, respectively, including virus quantification by plaque assay using Vero cells. Nairobi mosquito population exhibited a significantly higher midgut infection rates (16.8%) compared to the Kilifi population (9%; p=0.0001). Midgut infection rates among the populations varied with temperature, with a significantly higher infection rate observed in mosquitoes from Nairobi at high (21.3%) compared to low temperature (12.0%; P=0.0037). Similarly, for Kilifi mosquito population, a significantly higher infection rate was recorded at high (11.6%) relative to low temperature (6.8%; P=0.0162). Disseminated infection was higher among the Kilifi mosquito population (40.7%) than in mosquitoes from Nairobi (10.3%; P<0.0001). The findings show that Aedes aegypti mosquito populations from Nairobi and Kilifi are susceptible to dengue-2 virus, with only Kilifi Ae. aegypti population supporting disseminated infection. It was observed that infected Ae. aegypti mosquitoes are able to vertically transmit the virus to their progeny. This is the likely mechanism by which the virus is maintained and propagated among its natural hosts.