West Nile virus has been detected in the UK for the first time after being found in mosquitoes collected from the River Isle near Retford

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 during July 2023. The findings, published today (21) came through the Vector-Borne RADAR programme which tests mosquitoes for emerging threats.

The virus was detected 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.

To date, there have been no human cases of locally acquired West Nile Virus in the UK. The main risk of West Nile Virus for UK residents continues to be travel to overseas areas, including parts of Europe, which have already been affected by the disease.

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. But they 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 encourages a large number 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.”

What is West Nile Virus?

West Nile Virus is a disease usually found in birds, and typically circulates through bird-biting mosquitoes.

Occasionally, mosquitoes may bite both birds and humans or birds and horses, and in rare cases can transmit the virus to humans or horses. 

Most people infected with West Nile Virus show no symptoms or present with mild influenza-like symptoms such as fever, headache or myalgia, swollen lymph nodes and a rash. While most recover from the infection within a few days, a small number of cases (under 1%) can cause more severe illness. 

West Nile Virus is endemic in various regions across the globe, including Europe, Africa, the Middle East, West and Central Asia, and North America, as well as South America, USA and Australia.