The virus has caused outbreaks of disease in Africa, Asia, Eastern Europe and the Middle East since 1937, but it did not appear in the United States until 1999. After first being discovered in birds and people in the metropolitan New York City area, it spread westward across the US and into Canada and Mexico. It is not known how West Nile virus arrived in the United States.
Wild birds become infected with West Nile virus and carry the virus in nature. Mosquitoes become infected after feeding on infected birds. People bitten by a mosquito carrying West Nile virus may have no symptoms at all or they may become ill with symptoms ranging from mild to severe. Horses, crows, hawks, owls and eagles are especially susceptible to West Nile virus disease, whereas the virus rarely causes illness in dogs, cats or chickens. Report dead birds