West Nile virus

1:  a single-stranded RNA virus of the genus Flavivirus (species West Nile virus) that causes an illness marked by fever, headache, muscle ache, skin rash, and sometimes encephalitis or meningitis, and that is spread especially from birds to humans by mosquitoes chiefly of the genus Culex ◆West Nile virus is closely related to the viruses causing Japanese B encephalitis and Saint Louis encephalitis. West Nile virus causes unusually severe infections in crows and blue jays, according to one CDC-led study that measured the number of virus particles in the birds' blood …—Stephen S. Hall, Smithsonian, July 2003 Of 5780 cases of arboviral disease reported in 2012, West Nile virus infection accounted of 5674, or 98% of the total, researchers reported in the Morbidity and Mortality Weekly Report.—Rebecca Voelker, The Journal of the American Medical Association, 21 Aug. 2013

2 or West Nile fever :  the illness caused by West Nile virus West Nile virus is such a disease. Last week, President Clinton declared an emergency in areas of New Jersey affected by the virus …—James Ridgeway, The Village Voice, 14 Nov. 2000 … residents are being urged to stay indoors while trucks spray insecticides through the streets to ward off outbreaks of West Nile fever, a mosquito-spread disease that last summer sickened dozens and killed seven.—Joannie Schrof Fischer et al., U.S. News & World Report, 7 Aug. 2000—see west nile encephalitis