STORY
West Nile virus has been detected in UK mosquitoes for the very first time, health authorities have confirmed. Fragments of West Nile virus (WNV) genetic material were found in two pools of Aedes vexans mosquitoes collected from wetlands on the River Idle near Gamston, Nottinghamshire, during July 2023, as part of the Vector-Borne RADAR surveillance programme run by the UK Health Security Agency (UKHSA) and the Animal and Plant Health Agency (APHA). Although this marks the first evidence of WNV in British mosquitoes, officials stress there is currently “no evidence to suggest ongoing circulation of the virus in birds or mosquitoes in the UK” and the risk to the general public remains “very low”.
West Nile virus belongs to the Flaviviridae family—a group that also includes dengue and yellow fever viruses—and typically circulates between birds and mosquito vectors. In rare instances, infected mosquitoes can transmit the virus to humans or horses, causing anything from mild, flu-like symptoms to severe neurological diseases such as meningitis or encephalitis. Most human infections are asymptomatic, but around one in five people may experience fever, headaches or skin rash, while fewer than 1% develop neuroinvasive disease, which can carry a mortality rate of up to 17%. The Vector-Borne RADAR project pooled mosquitoes into groups of ten for polymerase chain reaction (PCR) testing. Of the 200 pools tested from the Nottinghamshire site, only two returned positive for WNV fragments, with the remaining 198 testing negative. This rigorous approach is designed to provide “early warning of potential threats” and enable the swift enhancement of disease surveillance and control activities, ensuring prompt testing for any suspected cases of encephalitis of unknown origin.
Dr Meera Chand, UKHSA Deputy Director for travel health, zoonoses, emerging infections, respiratory and tuberculosis, reassured the public “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”. Health professionals have been advised to consider WNV in unexplained encephalitis cases and to send samples to the UKHSA’s Rare and Imported Pathogens Laboratory as a precautionary measure.
Experts warn that rising temperatures and climate change are extending the range of mosquito-borne diseases northwards. Dr Arran Folly, lead arbovirologist on the RADAR project at APHA, noted that “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”. As the UK experiences warmer summers, non-native mosquito species may find the climate increasingly hospitable, underscoring the need for ongoing monitoring. To date, there have been no locally acquired human or equine cases of West Nile virus in the UK, seven travel-associated human cases have been recorded since 2000, and the main risk to UK residents remains travel to endemic regions overseas. Meanwhile, members of the public are encouraged to reduce standing water around homes, use insect repellent, and wear loose-fitting clothing to minimise mosquito bites.