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

However, some species, including Aedes aegypti, can carry and transmit diseases, such as dengue, chikungunya, West Nile virus, yellow fever and Zika virus. —Mary Walrath-Holdridge, USA Today, 29 Oct. 2025

While there is no cure for West Nile virus, health officials said, supportive care in hospitals can help people afflicted with severe neuroinvasive symptoms. —Cathie Anderson, Sacbee.com, 6 Oct. 2025

To reduce the risk of mosquito bites and West Nile virus, health officials recommend using insect repellent and wearing long sleeves and long pants when outdoors, especially during peak mosquito activity at dawn and dusk. —Caroline Neal, Louisville Courier Journal, 2 Oct. 2025

Most people who develop a fever and other less severe symptoms from West Nile virus recover completely. —Madeline Heim, jsonline.com, 1 Oct. 2025

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