West Nile virus

noun

variants or less commonly West Nile

1

: a flavivirus (Orthoflavivirus nilense) 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

2

or West Nile fever : the illness caused by West Nile virus

Examples of West Nile virus in a Sentence

Recent Examples on the Web

Besides being nuisances, many types carry diseases including West Nile virus, encephalitis, and canine heartworm. — Arricca Elin Sansone, Southern Living, 3 July 2026

And the condition has not yet made the list of diseases, such as Lyme disease and West Nile virus, tracked by the National Notifiable Diseases Surveillance System, in which states voluntarily inform federal health officials of case counts. — Erika Edwards, NBC news, 2 July 2026

Sacramento County reported its first human infection of West Nile virus this year, county health officials announced Thursday. — Reeti Malhotra july 2, Sacbee.com, 2 July 2026

Public health officials routinely trap and test mosquitoes throughout the summer to monitor for West Nile virus activity. — Brittany Miller, FOXNews.com, 1 July 2026

Word History

Etymology

from West Nile province of Uganda, where the virus was isolated in 1937

First Known Use

1940, in the meaning defined at sense 1

Rhymes for West Nile virus

• adenovirus
• baculovirus
• coronavirus
• enterovirus
• poliovirus
• antivirus
• herpesvirus
• parvovirus
• reovirus
• retrovirus
• rhinovirus
• rotavirus

Medical Definition

West Nile virus

noun

variants also West Nile

1

: a flavivirus (Orthoflavivirus nilense) 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

Note: West Nile virus is closely related to the viruses causing Japanese 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

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

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

… 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

see west nile encephalitis