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.

---

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.

---

Etymology

Origin of West Nile virus

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

Example Sentences

See Examples For:

West Nile virus

Last year, Orange County’s vector control detected West Nile virus in four mosquito pools.

From Los Angeles Times ● Jul. 8, 2026

He had developed a neuroinvasive disease as a complication from contracting West Nile virus.

From MarketWatch ● Jul. 7, 2026

Health authorities are warning residents to take precautions after the deadly West Nile virus was detected in a mosquito caught in the San Gabriel Valley.

From Los Angeles Times ● Jun. 30, 2026

The southern house mosquito, known as culex quinquefasciatus, is the region’s most common vector of West Nile virus, according to the San Gabriel Valley Mosquito and Vector Control District.

From Los Angeles Times ● Jun. 30, 2026

Still, threats remain: Rat poison, electrocution on power lines, lead poisoning, West Nile virus and avian flu top the list.

From Los Angeles Times ● Mar. 3, 2026