Comparison of West Nile Virus exposure in horses and infection rates in the mosquito Culex tarsalis in Montana.

Abstract

I compared infection rates of West Nile Virus in the vector Culex tarsalis and exposure of the virus via antibody presence in horses. This research was performed to determine which method is more efficient at detecting the virus, thus contributing to viral public risk assessment for the state of Montana. Mosquitoes and horse blood came from similar locations, including the Helena area and the Fort Belknap Indian Reservation. Mosquitoes were trapped throughout the summer using carbon dioxide baited CDC light traps and were homogenized before RNA was extracted and finally tested for WNV with RT-PCR. Horse sera were extracted in mid-September and tested for WNV antibodies using IgM ELISA, where positive results indicate viral exposure. Pools of mosquitoes that tested positive by RT-PCR were analyzed with an Excel program for infection rate calculations and compared to numbers of positive horse sera. Mosquito infection rates were higher than horses detected positive by ELISA, indicating that mosquito surveillance is a more efficient means of detecting viral presence.