Distribution of bird reservoir hosts for West Nile Virus in Montana
West Nile virus (WNv) is an arthropod-borne flavivirus that was first detected in the United States in 1999. By 2004 it had spread to 48 states and, to date, it has been the source of greater than 29,000 cases of human infection. WNv is maintained through an avian-mosquito transmission cycle, with birds serving as the primary vertebrate hosts for the amplification of the virus. Previous studies have shown Passeriform birds to be some of the most virulent competent hosts for the virus, producing adequate viremia counts for continuation of the transmission cycle. Associations were analyzed between mosquito populations and total bird abundance, Passeriformes abundance, and virulent competent bird species abundance using data collected from sites across Montana. No temporal correlation was found between bird and Culex tarsalis (the most important mosquito vector in Montana) mosquito numbers across the summer sampling period. However, a positive correlation was observced between passerine abundance and total mosquito numbers. These findings suggest that passerine abundance is associated with mosquito population numbers, which may result in an increased risk for WNv transmission.