West Nile virus found in UK mosquitoes for first time

West Nile virus has been detected in mosquitoes in the UK for the first time, health officials have confirmed.

The UK Health Security Agency (UKHSA) and Animal and Plant Health Agency (APHA) identified fragments of the virus’s genetic material in mosquitoes collected from wetlands near Gamston, close to Retford in Nottinghamshire, during July 2023. The findings, published on 21 May 2025, came through the Vector-Borne RADAR programme which tests mosquitoes for emerging threats.

The virus was detected using PCR tests in two out of 200 pooled mosquito samples, each pool containing ten Aedes vexans mosquitoes. While the remaining 198 pools tested negative, the result marks the first recorded presence of West Nile virus in mosquitoes in the UK.

West Nile virus is primarily a bird disease transmitted by mosquitoes. It can occasionally be passed to humans or horses through mosquito bites. Most human cases show no symptoms, but in rare cases it can cause serious illness including encephalitis.

UKHSA said there is no current evidence of the virus circulating in birds or mosquitoes in the UK, and the public health risk remains very low. Nevertheless, officials are enhancing surveillance and have issued advice to health professionals to test for the virus in cases of unexplained encephalitis.

Dr Meera Chand, Deputy Director at UKHSA, said:
“While this is the first detection of West Nile Virus in mosquitoes in the UK so far, it is not unexpected as the virus is already widespread in Europe. The risk to the general public is currently assessed as very low.”

The infected mosquitoes were found near the River Idle, where seasonal flooding and poor drainage support localised high densities of Aedes vexans mosquitoes. This species is native to the UK and is known to cause nuisance biting in areas such as those villages bordering the river.

Dr Arran Folly, lead of the Vector-Borne RADAR project, commented:
“The detection of West Nile virus in the UK is part of a wider changing landscape, where, in the wake of climate change, mosquito-borne diseases are expanding to new areas. Only through continued surveillance can we assess the risk to animal and public health.”

To date, no locally acquired human or animal cases of West Nile virus have been reported in the UK. Seven travel-related human cases have been recorded since 2000.

The Vector-Borne RADAR project, which includes input from ZSL’s Institute of Zoology and the British Trust for Ornithology, has tested more than 32,000 mosquitoes. It forms part of a broader effort to track and respond to the emergence of mosquito-borne diseases in the UK.

Dr Jolyon Medlock, Head of Medical Entomology and Zoonoses Ecology at UKHSA, encouraged the public to remain aware of mosquito activity:
“Our surveillance monitors for mosquitoes across Britain to understand their distribution and activity. People experiencing nuisance biting can submit photos or samples to our mosquito surveillance scheme.”

UKHSA advises taking simple steps to reduce the risk of mosquito bites, including wearing long-sleeved clothing, using DEET-based insect repellents, and managing water containers in gardens where mosquitoes may breed.