West Nile USA

About West Nile USA

West Nile Virus was first detected in the Western Hemisphere in August 1999 when an unusual cluster of encephalitis cases occurred in Queens, New York. The virus infected birds and humans simultaneously, initially confusing investigators who suspected St Louis encephalitis. The CDC identified West Nile Virus in September. By the end of 1999, there were 62 human cases and 7 deaths. The virus spread across the entire continental United States by 2004, reaching approximately 9,800 cases and 264 deaths at its peak in 2003. West Nile is transmitted by Culex mosquitoes from birds to humans. Crows were particularly susceptible, and dead crows served as sentinels for virus spread. The virus is now endemic in the US, with hundreds to a few thousand neuroinvasive cases reported each year. Approximately 1 in 150 infected people develop severe neurological disease. The introduction of West Nile demonstrated how a pathogen could establish permanent endemicity in a new continent. The mode of introduction remains unknown.