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  "path": "/2026/06/01/what-is-west-nile-virus-and-is-it-found-in-the-uk/",
  "publishedAt": "2026-06-01T15:00:15.000Z",
  "site": "https://ukhsa.blog.gov.uk",
  "tags": [
    "West Nile virus",
    "dengue",
    "yellow fever",
    "Japanese encephalitis",
    "2024, 19 European countries reported human cases",
    "Fragments of WNV genetic material were detected in UK mosquitoes in samples from 2023",
    "countries where it is common",
    "visit TravelHealthPro for up-to-date travel health advice",
    "mosquito Culex modestus",
    "please report it to Mosquito Watch",
    "report it to the Animal and Plant Health Agency",
    "national contingency plan",
    "map of risk levels across England in the West Nile virus plan",
    "surveillance, horizon scanning, clinical advice and risk assessments",
    "invasive mosquito surveillance",
    "Centre for Climate and Health Security",
    "One Health Vector-Borne Disease annual surveillance reports"
  ],
  "textContent": "West Nile virus (WNV) is a virus spread primarily through the bites of infected mosquitoes. It belongs to the same family of viruses as dengue, yellow fever and Japanese encephalitis. The virus circulates naturally between birds and mosquitoes, and humans or horses can be infected when bitten by a mosquito that has previously fed on an infected bird. Neither humans nor horses can pass the virus back to mosquitoes, so an infected person or animal does not directly trigger a local outbreak on their own.\n\n## **Where does it come from, and is it spreading?**\n\nWNV was first identified in Uganda in 1937. It is now endemic in parts of Europe, the United States, Canada and the Caribbean. In 2024, 19 European countries reported human cases. Transmission in Europe typically peaks during summer and early autumn, when mosquitoes are most active. Climate change is increasing the risk to the UK - migratory birds arriving here each spring from affected regions could carry the virus, and warming temperatures are making conditions more favourable for the mosquitoes that could spread it locally. Fragments of WNV genetic material were detected in UK mosquitoes in samples from 2023 but there have been no detections of WNV in UK mosquitoes since then.\n\n## **What are the chances of catching it in England right now?**\n\nTo date, there have been no human cases of WNV acquired in the UK. The main risk for UK residents remains travel to countries where it is common. That said, the risk is not zero and is gradually increasing, which is why surveillance and preparedness planning are actively under way.\n\n## **What are the symptoms?**\n\nMany people infected with WNV have no symptoms at all, or experience only mild illness such as fever, headache, muscle aches and a rash, which typically resolves within a week. However, around 1 in 150 cases develop serious disease affecting the brain and nervous system, such as meningitis, encephalitis, or sudden severe muscle weakness. There is no vaccine or specific treatment for humans; care is supportive. People over 50, and those with underlying conditions such as diabetes, cancer, hypertension or kidney disease, are at greatest risk of severe illness. The risk of death is highest in those aged over 70.\n\n## **What can I do to protect myself?**\n\nThe most effective protection is avoiding mosquito bites, particularly during the biting season between May and September. Practical steps include using insect repellent, wearing long sleeves and trousers at dawn and dusk, and removing standing water around your home where mosquitoes can breed eg emptying paddling pools after use. If you are travelling to a country where WNV is circulating, visit TravelHealthPro for up-to-date travel health advice before you go.\n\n## **Which mosquitoes present a risk in England?**\n\nNot all mosquitoes can transmit WNV to humans. The key risk comes from so-called ‘bridge vectors’ - species that bite both birds and mammals. The principal bridge vector in Europe is the mosquito Culex modestus, associated with wetland habitats, and Culex molestus in urban habitats. Culex modestus has been established in parts of England since at least 2010, particularly around the Thames Estuary, the Cambridgeshire Fens and the south coast. Its range is expanding, likely due to climate change. Mosquito biting season in the UK typically runs from May to September.\n\nCulex molestus is not common, but can cause nuisance biting in urban areas, associated with underground flooding. If you experience nuisance biting, please report it to Mosquito Watch so we can investigate.\n\n## **Can West Nile virus affect animals?**\n\nYes. Birds are the main reservoir for the virus. Corvids (such as crows and rooks) and birds of prey appear particularly susceptible and may show neurological symptoms like loss of coordination or tremors. Horses can also be infected and may show weakness, stumbling or paralysis; between 30 and 45 per cent of horses showing clinical signs do not survive. A vaccine is available for horses. If you suspect a horse may be infected, you are legally required to report it to the Animal and Plant Health Agency.\n\n## **How is the government responding?**\n\nThe UK Health Security Agency (UKHSA), Defra and the Animal and Plant Health Agency have jointly published a national contingency plan setting out a coordinated response across 5 risk levels - from areas currently considered ecologically unsuitable for transmission, through to areas with confirmed human cases. Parts of England are currently at level 1, which means that there are 1 or more sites in the local authority that have bridge vectors and have seen nuisance biting during 2024 and 2025.\n\nYou can see a map of risk levels across England in the West Nile virus plan.\n\nThe national contingency plan involves seasonal active mosquito surveillance, continuous mosquito and wildlife surveillance, blood safety measures, clinician awareness, and - if the risk escalates - public information campaigns and mosquito control.\n\n## **What is UKHSA's role in handling disease spread by mosquitoes?**\n\nThe UK Health Security Agency (UKHSA) monitors the risks of vectors and vector-borne diseases to public health through surveillance, horizon scanning, clinical advice and risk assessments.\n\nUKHSA scientists collaborate with academic partners to undertake and publish research that is relevant to their work, such as on invasive mosquito surveillance in the United Kingdom.\n\nOur Centre for Climate and Health Security collates and translates complex data on mosquito populations into evidence-based guidance for preparedness and response to emerging vector-borne diseases.\n\nAs of 2026, UKHSA is producing One Health Vector-Borne Disease annual surveillance reports that provide data on the geographical presence and distribution of disease-transmitting vectors and vector-borne diseases, monitoring changes over time to inform assessments of risks to public health.",
  "title": "What is West Nile virus and is it found in the UK?",
  "updatedAt": "2026-06-01T15:00:15.000Z"
}