First Detection of West Nile Virus in the UK: What It Means for Public Health

In an important development, the UK has recently identified traces of the West Nile virus in mosquitoes, marking the first time the virus has been detected on British soil. According to a report from the UK Health Security Agency, mosquitoes collected from marshlands in south-east England tested positive using PCR tests, which detect segments of the virus's genetic material. While this detection does not immediately indicate an imminent outbreak, it raises awareness about the potential risks.

West Nile virus is a mosquito-borne infection first identified in Uganda in 1937. It belongs to the same family as viruses like dengue and yellow fever. The primary vectors are mosquitoes from the Culex genus, especially Culex pipiens, which mainly feeds on birds. These birds serve as the main hosts for the virus, creating a cycle where the infection circulates between birds and mosquitoes. Occasionally, mosquitoes transmit the virus to humans and other mammals.

Most human infections with West Nile virus are asymptomatic—about 80% of people show no symptoms. When symptoms do present, they tend to be mild, including fever, fatigue, headaches, body aches, and nausea. However, in approximately 1 in 150 cases, the virus can cause severe illnesses such as encephalitis (brain inflammation) and meningitis. Risk factors include age, with older adults over 50 being more vulnerable.

The recent finding in UK mosquitoes is believed to have resulted from migratory birds carrying the virus from infected regions elsewhere. These birds likely transferred the virus during their migration, which was then picked up by local mosquitoes during feeding. The surveillance program that uncovered this finds mosquitoes in the region testing positive for viral genetic material, but it's important to note that detection via PCR does not necessarily mean the mosquitoes can transmit the virus at that moment.

Climate plays a significant role in the potential spread of West Nile virus. The cooler summer temperatures in the UK have historically limited the development of the virus inside mosquitoes, as temperatures below 15°C slow or prevent the virus's replication. For sustained transmission, warmer and prolonged hot weather is typically required, which has not yet been the case in the UK. Nevertheless, climate change, resulting in warmer summers, could create more conducive conditions in the future.

Comparatively, West Nile virus has caused widespread outbreaks in countries like Greece, Israel, Russia, and the US, where warm climates foster mosquito activity. The US reported over 60,000 human cases since the virus's emergence there in 1999, alongside bird and horse outbreaks. European countries like Italy, Greece, and Spain have also seen increased cases, mainly during hot summers.

Although the mosquito detection in the UK is noteworthy, experts reassure that the immediate risk to the public remains very low. No human cases have been reported in the UK to date. The primary precaution for travelers and residents remains the same: use mosquito repellent, wear long sleeves and trousers, especially during evening hours when mosquitoes are most active. Continuous surveillance, awareness, and climate monitoring are vital to anticipate and prevent potential future transmission.

This event underscores the importance of ongoing mosquito control efforts and climate adaptation strategies to proactively manage the risk of mosquito-borne diseases in the UK and beyond. Source: https://medicalxpress.com/news/2025-05-west-nile-virus-uk.html