Predictable ecology and geography of West Nile virus transmission in the central United States.

West Nile virus (WNV) arrived in North America and spread rapidly through the western hemisphere. We present a series of tests to determine whether ecological factors are consistently associated with WNV transmission to humans. We analyzed human WNV cases in the states of Illinois, Indiana, and Ohio in 2002 and 2003, building ecological niche models to associate WNV case occurrences with ecological and environmental parameters.