WEST NILE VIRUS
► Definition: viral disease that affects the central nervous system. Technically, “West Nile virus” (WNV) is the agent that causes the disease “West Nile encephalomyelitis,” but people commonly use the name of the virus to refer to the illness.
► Transmission: WNV is a flavivirus carried by birds and spread by mosquitoes. Most wild birds are asymptomatic carriers of the virus with the exception of ravens, crows and other corvids, for which WNV is often fatal. Dead ravens and crows are often an indicator of an outbreak in a local area. Horses are considered dead-end hosts; that is, once infected they do not directly infect others.
WNV is a relative newcomer among U.S. diseases. The virus was first identified in the West Nile river region of Uganda in 1937, and for more than 50 years its range seemed to be limited to Africa, the Middle East and parts of Europe and western Asia as well as Australia. In 1999, however, the first