Modeling movement of West Nile virus in the Western hemisphere.

We modeled West Nile virus (WNV) movement rates and patterns based on a migratory bird agent (the Swainson's Thrush) and a resident bird agent (the House Sparrow), and compared the results of these models with actual movement data to investigate the likelihood that the pattern of WNV outbreaks observed in the New World was consistent with migrant bird-mediated spread, as reported from the Old World. We found that, contrary to Old World patterns, WNV activity in the Western Hemisphere does not seem consistent with movement by infected migrant birds. Instead WNV spread appears best explained by a non-directional movement, perhaps that of dispersing resident birds.