West Nile virus: a member of the
Flavivirus genus first identified in 1937 in the West Nile district
of Uganda. The virus is passed between birds by mosquitoes, which
in turn can infect humans through bites. The illness first appeared
in the Western Hemisphere in 1999 and is characterized by fever,
nausea, vomiting, headache, myalgia, and in rare instances leads
to a severe neurologic disease.