The introduction and extensive expansion of WNV in the US in the last three years is having a dramatic impact on native wildlife. The disease continues to cause significant mortality in a variety of bird species throughout the eastern US, particularly in American crow and blue jay populations. As the virus expands to new habitats in the southern, midwestern and western states, new bird species will be at risk and different patterns of transmission will develop. In the western states, many additional species of Corvidae (crows, jays, ravens, magpies and nutcrackers) may be affected. Once it becomes well established in states with warm climates, like Florida where mosquitoes are active year round to sustain almost continuous transmission; these states could serve as annual sources of WNV for migratory birds to re-introduce the virus to northern states in the spring. The rapid increase in geographical distribution of WNV activity that has occurred throughout the eastern US and the rapid increase in the infection and mortality rates in birds during the last three years indicate the emergence of an epizootic disease of major importance to North American birds.
