For the first time ever, West Nile Virus has been detected in UK mosquitoes, signaling potential new health challenges as climate patterns shift across Europe.

At a Glance

• Genetic fragments of West Nile Virus were discovered in Aedes vexans mosquitoes from wetlands near Nottinghamshire in July 2023
• The virus likely arrived via migratory birds, with no locally acquired human or horse cases reported to date
• Health authorities maintain the risk to the public remains very low, but surveillance has intensified
• Scientists warn climate change may increase the UK’s vulnerability to this and similar viruses in coming years
• Over 30,000 mosquitoes and 300 birds from high-risk areas were tested in the national surveillance program

Historic Detection Marks Surveillance Milestone

The UK Health Security Agency (UKHSA) has confirmed the first-ever detection of West Nile Virus in British mosquitoes. Genetic fragments of the virus were found in Aedes vexans mosquitoes collected in July 2023 from wetlands near Gamston, Nottinghamshire. This significant finding emerged from the Vector-Borne RADAR surveillance program, a joint initiative between UKHSA and the Animal and Plant Health Agency that tested over 30,000 mosquitoes and 300 birds from high-risk areas throughout England in 2023 and 2024.

West Nile Virus primarily circulates among bird populations, with humans becoming infected only when bitten by mosquitoes that previously fed on infected birds. While this detection represents a monitoring breakthrough, health officials emphasize that no locally acquired human or horse infections have been documented in the UK. All other mosquito and bird samples tested during the surveillance program have returned negative results for the virus.

Public Health Implications

Dr. Meera Chand from the UKHSA noted that finding West Nile Virus in UK mosquitoes was “not unexpected,” as the virus is already widespread across Europe. The agency currently assesses the risk to the general public as “very low,” though healthcare professionals have been advised to consider West Nile Virus testing for patients presenting with unexplained encephalitis. Most human infections cause mild or no symptoms, but in rare cases, especially among older individuals, the virus can trigger serious neurological complications.

“The detection of West Nile virus in UK mosquitoes is a significant finding, especially as our climate changes. The virus is transmitted among birds by mosquitoes, and humans become infected when they are coincidentally bitten by an infected mosquito. It is most likely the virus arrived in the UK via an infected migrating bird. Climate change impacts on numbers and types of mosquitoes and allows emerging viruses to become established, and we are likely to see more of this, and similar viruses in the future.”, said Prof Tom Solomon.

The virus belongs to the flavivirus family, which includes other concerning pathogens like dengue, Zika, and yellow fever. Although West Nile Virus has been present in mosquitoes, there’s no evidence yet that the infected mosquito populations will establish permanently in the UK climate. However, scientists caution that extended warm weather periods could increase that possibility.

Climate Change Concerns

Experts have highlighted the role of climate change in potentially expanding the range of mosquito-borne diseases into previously unaffected regions. West Nile Virus is currently endemic in parts of Africa, Asia, the Americas, and southern Europe, with its geographic distribution steadily expanding northward. Britain’s changing climate conditions may create more favorable environments for both the virus and its mosquito vectors.

“Climate change isn’t just a future threat; it’s already reshaping disease patterns. As the climate continues to warm and rainfall patterns shift, the risk of diseases such as West Nile Virus spreading to Europe has significantly increased. This is not a new phenomenon, Europe has become increasingly more hospitable for West Nile Virus since the 1980s, with a period of rapid warming creating the perfect conditions for the virus to spread. Countries like the UK that were once considered low risk are now more vulnerable to outbreaks – a concern only amplified by the fact that there are currently no approved treatments for West Nile Virus.”, said Felipe Colón.

The Aedes vexans mosquito species involved in this discovery is native to the UK and typically breeds in natural wetlands and water-collecting containers. These mosquitoes can cause nuisance biting but have not previously been linked to virus transmission in Britain. This detection underscores the importance of continued robust disease surveillance systems to monitor and manage potential future outbreaks as environmental conditions evolve.