This week, UK scientists confirmed something that, to me, was destined to happen. For the first time, West Nile Virus (WNV) have been detected in mosquitoes collected in Britain. To be clear, the scientists detected fragments of the virus. There is no evidence of an active outbreak, and no humans or animals have been infected. But it is a signal—a small but significant one—of how climate change is rewriting the rules of infectious disease geography.
Table of Contents
- How is climate change linked to mosquito-borne disease in the UK?
- What is West Nile Virus and how does it spread?
- Where was West Nile Virus found in UK mosquitoes?
- How is the UK managing mosquito-borne disease risk?
- Could tropical infections become common in the UK?
How is climate change linked to mosquito-borne disease in the UK?
Mosquito-borne infections, like West Nile Virus, were previously thought to be diseases primarily of the tropics, areas around the Equator with intense heat and humidity. But the label “tropical disease” is increasingly obsolete.
West Nile Virus is carried by mosquitoes, circulates primarily in birds, and occasionally spills over to humans and horses, sometimes causing serious neurologic disease. The virus is endemic across much of the globe—from the Middle East and Africa to Europe and the Americas—but, until now, it had not been found in British mosquitoes.
That changed when researchers from the UK Health Security Agency and the Animal and Plant Health Agency, as part of its Vector-Borne RADAR project, tested thousands of mosquitoes from wetland areas in Nottinghamshire. In two samples of Aedes vexans mosquitoes, they found genetic traces of WNV. Note that these are just fragments, not live virus. While there is no evidence of ongoing transmission, the news is enough to raise worry about future outbreaks.
What is West Nile Virus and how does it spread?
West Nile Virus is classified as a vector-borne infection, akin to dengue and yellow fever. It typically circulates between birds and the mosquitoes that bite them. Occasionally, the virus spills over into humans and horses, where it can cause a range of illnesses—from mild febrile syndromes to life-threatening encephalitis. Most people infected never develop symptoms, but the potential for severe disease remains, particularly in older adults or those with weakened immune systems.
Where was West Nile Virus found in UK mosquitoes?
The fragments were detected in mosquito samples collected from wetlands near the River Idle in Nottinghamshire as part of . Specifically, two pooled samples of Aedes vexans mosquitoes—species that are native to the UK and sometimes found in high densities near summer-flooded riverbanks—tested positive for WNV genetic material. Out of 200 tested pools, only two returned a positive result, underscoring how rare the detection was, but also how meaningful.
How is the UK managing mosquito-borne disease risk?
The UK Health Security Agency has classified the risk to the public as very low and has issued guidance to healthcare professionals to consider WNV testing for unexplained encephalitis. Surveillance programs have been intensified in response, including continued monitoring of mosquito populations at wetlands, travel hubs, and areas with potential for mosquito introduction through trade and transit.
The broader Vector-Borne RADAR program is working not only to detect viruses early, but to understand the complex ecology of how they enter and potentially establish in the UK. These early warning systems are essential for preventing future outbreaks and enabling rapid response.
Could tropical infections become common in the UK?
What this detection tells us is that the UK’s climate is becoming more accommodating to pathogens once thought foreign. Mosquito species that can spread disease are finding it easier to survive and thrive, and the viruses they carry are traveling with them. And this is not an isolated case. Across Europe, the range of mosquito-borne infections has expanded in recent years, including dengue in France and chikungunya in Italy. Climate change is one of the most important drivers of emerging infectious diseases.
We’ve spent decades thinking of certain infections as someone else’s problem, afflictions confined to equatorial latitudes or the distant global South. But rising temperatures, erratic precipitation, and warming wetlands are erasing those old boundaries. Disease vectors are moving, and with them, so are the pathogens they carry.