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

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Example Sentences

See Examples For:

West Nile virus

The California Department of Public Health reports that West Nile virus activity in the state, which is transmitted from infected mosquitoes, has reached a five-year high, with over 250 cases to date and 19 fatalities.

From The Wall Street Journal ● Oct. 9, 2026

Health officials say mosquito season typically runs from June to October and the region is on track for one of its most severe West Nile virus seasons in recent memory.

From Los Angeles Times ● Sep. 22, 2026

After an abnormally warm winter and a blistering March heat wave, California has seen a surge in mosquito activity that has driven West Nile virus activity to a five-year high.

From Los Angeles Times ● Aug. 21, 2026

West Nile virus survives in nature in several types of birds and is transmitted to humans by the bites of mosquitoes that feed on infected birds.

From Los Angeles Times ● Aug. 21, 2026

He wrote in 2024 about a bout with West Nile virus that left him in the hospital and struggling to remember facts.

From The Wall Street Journal ● Jul. 31, 2026

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