What is West Nile virus?

West Nile virus (WNV) is a mosquito-borne virus belonging to the flavivirus family, which also includes dengue, Zika, and yellow fever viruses. The virus originated in Africa but has since spread to parts of Europe, Asia, the Middle East, and North and South America.

Mosquitoes (particularly Culex species) become infected by drinking the blood of infected birds. These mosquitoes can then transmit the virus to humans and other mammals, such as horses. Human-to-human transmission is rare, but can occur through blood transfusions, organ transplants, and pregnancy or breastfeeding.

Most people (80%) who become infected experience no symptoms. Some people experience mild symptoms such as fever, headache, muscle aches, rash, and fatigue. One in 100 develops serious neurological symptoms such as encephalitis, meningitis, and muscle weakness or paralysis (sometimes resembling polio). Symptoms usually begin 3 to 14 days after being bitten by an infected mosquito.

In recent years, there have also been reports of locally transmitted West Nile virus infections in Europe, including in Italy, Greece, Hungary, Germany, and the Netherlands (several human cases since 2020, primarily in the Utrecht region).

Treatment consists of supportive measures such as rest, pain relief, and hospital care for severe symptoms. There is no vaccine for humans (although there is one for horses in some countries). Preventing mosquito bites is the best prevention. Use products containing DEET.

Source: https://www.who.int/news-room/fact-sheets/detail/west-nile-virus

Author: Prof. Dr. Dirk Devroey - Latest update: 2025-08-06 - Copyright: Clinifacts 2026