Evaluation of Lamu and Trans Nzoia Populations of Aedes Aegypti as Chikungunya Virus Vectors Under two Different Incubation Temperatures

Abstract

The rate at which the chikungunya virus (CHIKV) infects and disseminates in Aedes aegypti can be influenced by temperature which affect the distribution and incidence of vector-borne diseases. The first chikungunya fever epidemic in Kenya occurred in Lamu Island in 2004/05. This study investigated the vector competence of Ae. aegypti for CHIKV from Lamu and Tans nzoia areas and the influence of varying Extrinsic Incubation Temperature (EIT) of 32°C and 26°C that resembles those in the two regions. Four-day old mosquitoes were exposed to CHIKV through a membrane feeding. They were then incubated in temperatures mimicking the mean annual temperatures for Trans-Nzoia (26°C) and Lamu (32°C). The midgut infection rates (MIR) of Ae. aegypti sampled from Lamu region was significantly (p=0.0037) higher than those sampled from Trans nzoia with statistically significant difference observed for the coastal Ae. aegypti at EIT 26°C and at 32°C. The MIR of Ae. aegypti from Trans nzoia was significantly (p=0.0004) affected by the EIT, with mosquito reared at EIT 32°C exhibiting higher MIR than those reared at EIT 26°C. There was a significant (p=0.0331) interactive effects of the region, EIT and DPI on MIR. The DIR-L and DIR-H was higher in mosquitoes sampled from Lamu regardless of the EIT while those from Trans nzoia, dissemination rates were significantly higher at higher EIT of 32°C. These findings show a clear difference between the two mosquito populations in their ability to disseminate infection with influence in high temperature enhancing vector competence. This could explain the distribution and spread of CHIKV into susceptible host. Such information is insightful and may assist the public health sector to focus surveillance and initiate vector control strategies and responses when there is a potential threat in prone areas.