The West Nile virus epidemic in North America: 1999-2002

West Nile virus (WNV) has spread across the North American continent, since its introduction in the summer of 1999. The virus first appeared in Canada in Ontario, Quebec, and Manitoba in 2001, Saskatchewan in 2002, and Alberta in 2003. At present, the virus is widespread in the southern portions of all the Prairie provinces, Ontario, Quebec, and Nova Scotia. WNV is an arthropod-borne virus, circulating primarily between birds and mosquitoes; however, it can affect mammals, including humans and horses as dead-end hosts. A complex interdependence between mosquitoes, climate, and bird species drives the amplification of the virus. Prevention is aimed at mosquito reduction and, in horses, improving immunity through vaccination. This issue of Large Animal Veterinary Rounds discusses the WNV epidemic in Canada with special reference to the disease in the Prairie Provinces.