West Nile virus

American  

noun

Pathology.

1. an illness caused by a chiefly mosquito-borne virus of the genus Flavivirus, characterized in a small percentage of infected persons by fever, headache, muscle weakness, and sometimes encephalitis or meningitis.

2. the virus that causes this illness.

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West Nile virus Scientific  

/ wĕstnīl /

1. An infectious disease caused by a virus of the genus Flavivirus, occurring in Africa, Asia, the Mediterranean, and parts of North America. The infection is transmitted by a mosquito and can cause mild illness as well as severe, sometimes fatal encephalitis and meningitis.

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Etymology

Origin of West Nile virus

First recorded in 1935–40; named after the West Nile region of Uganda

Example Sentences

West Nile virus affects around 2,000 Americans a year, according to the U.S.

From Los Angeles Times • Oct. 24, 2025

To avoid contracting West Nile virus, the CDC recommends reducing outside activities during the daytime, when mosquitos are most active.

From Los Angeles Times • Oct. 24, 2025

County have had severe disease and approximately 10% of patients with severe West Nile virus die from complications.

From Los Angeles Times • Sep. 18, 2025

West Nile virus is endemic in several regions across the world, including parts of South America and Europe, and has expanded in recent years.

From BBC • May 21, 2025

There have been no cases of West Nile virus in humans acquired in the UK to date - though there have been seven travel-related cases since 2000.

From BBC • May 21, 2025