West Nile Virus

West Nile virus has emerged in recent years in temperate regions of Europe and North America, presenting a threat to public, equine, and animal health. The most serious manifestation of West Nile virus infection is fatal encephalitis (inflammation of the brain) in humans and horses, as well as mortality in certain domestic and wild birds.

The first appearance of West Nile virus in North America occurred in 1999, with encephalitis reported in humans and horses, and the subsequent spread in the United States. As of May 2006, West Nile virus has been documented in the contiguous United States and the District of Columbia.