EQUUS - - The Core -

► 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

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