West Nile virus
West Nile virus (WNV) is a type of flavivirus (like dengue or Zika) that can cause a potentially serious infection in humans. WNV is found in birds and spreads to animals and humans via a bite from an infected mosquito. Most people infected with WNV do not any have symptoms or experience a very mild illness and fully recover. If symptoms are present, they are usually mild; a flu-like illness with fever, headache, muscle pain and a red, bumpy rash.
However, about one in150 people infected with WNV develop a more serious, potentially fatal illness, with a high fever, severe headache, neck stiffness, confusion, muscle weakness, trembling, convulsions and coma. Meningitis (inflammation of the protective lining surrounding the brain and spinal cord), encephalitis (brain inflammation) or acute flaccid paralysis (weak/floppy limbs) can also occur.
Some people, including older travellers, those with long term health problems and anyone with a weakened immune system (immunosuppression) are more at risk of getting seriously ill.
There is no specific drug or treatment for WNV infection. Supportive care in a hospital is essential for people with severe WNV.
While a bite from an infected mosquito is the commonest way to catch WNV, there are rare reports of non-mosquito spread, including during a blood transfusion or organ transplant. The UK's NHS Blood and Transplant service currently monitors UK blood donors who have visited WNV risk areas.
WNV does not spread directly between people, but there have been reports of infected mothers passing WNV to their babies during breastfeeding. The World Health Organization also advises there is one case of an infected pregnant woman passing WNV on to her unborn baby.
Risk areas
WNV was first discovered in a woman with fever in the West Nile area of Uganda in 1937. Since then, human WNV infections have been reported worldwide in every content, except Antarctica.
No WNV infections have ever been reported as caught locally in the United Kingdom (UK) although cases are sometimes reported in returned travellers. Mosquitoes (Culex modestus) that can spread WNV are present in some parts of the UK and in March 2025, fragments of WNV RNA were reported in female Aedes vexans mosquitoes in Nottinghamshire, England. The probability of a human outbreak of WNV in the UK is currently considered, at most; very low.
Prevention
All travellers visiting countries with WNV are at risk. Anyone spending long periods abroad is more likely to catch WNV, but even short trips are a risk. Travellers should be made aware of their WNV risk when visiting countries known to have reported cases or outbreaks. Updated country-specific WNV information is available from the 'Outbreaks' and 'Other Risks' section of our Country Information pages.
There is no vaccine or drug to prevent WNV. The only way to reduce the risk of getting infected is by avoiding mosquito bites as much as possible. All travellers should be advised about the importance of following good mosquito and insect bite prevention advice at all times. One type of mosquito that spreads WNV usually bites in the evening and at night, but other mosquitoes that can carry WNV bite during the day.
More detailed advice can be found in our WNV factsheet.
Resources
- European Centre for Disease Control and Prevention: Surveillance of West Nile virus in humans in Europe, weekly report
- UK Health Security Agency: Mosquito bite avoidance: advice for travellers
- UK Health Security Agency: West Nile virus: epidemiology, diagnosis and prevention
- US Centers for Disease Control and Prevention: Data and Maps for West Nile
- World Health Organization: West Nile Virus
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Recent West Nile virus Outbreaks
West Nile virus in USA
As of 3 November 2026, a total of 1,668 human cases of West Nile virus have been reported across 47 states in the United States. Of these, 1,285 cases were reported to be the neuroinvasive form. The highest number of cases were reported in California (452 cases), Arizona (112), and Texas (91 cases). Please see our Topics in Brief article for further details on West Nile virus.
As of 13 October, a total of 1,328 human cases of West Nile virus have been reported across 45 states in the United States. Of these, 1,004 cases were reported to be the neuroinvasive form. The highest number of cases were reported in California (310 cases), Arizona (95), and Texas (80 cases). Please see our Topics in Brief article for further details on West Nile virus.
Source: CDCAs of 1 September 2026, a total of 407 human cases of West Nile virus have been reported across 40 states in the United States. Of these, 285 cases were reported to be the neuroinvasive form. The highest number of cases have been reported in Arizona (88 cases), California (66 cases) and Texas (46 cases). Please see our Topics in Brief article for further details on West Nile virus.
Source: CDCAs of 11 August 2026, a total of 181 human cases of West Nile virus have been reported across 30 states in the United States this year. Of these, 129 cases were reported to be the neuroinvasive form. The highest number of cases have been reported in Arizona (73 cases), Texas (23 cases), and California (18 cases). Please see our Topics in Brief article for further details on West Nile virus.
Source: StateWest Nile virus in Slovakia
As of 28 October 2026, the first case of West Nile virus of 2026 has been reported in Trnavský kraj, Slovakia. Please see our Topics in Brief article for further details on West Nile virus.
West Nile virus in Albania
As of 16 October 2026, a total of seven cases of locally acquired West Nile virus have been reported in Albania during 2026. Please see our Topics in Brief article for further details on West Nile virus.
West Nile virus in Bulgaria
As of 16 October 2026, a total of seven cases of locally acquired West Nile virus have been reported in Bulgaria during 2026. Please see our Topics in Brief article for further details on West Nile virus.
