The first detection of West Nile Virus (WNV) in UK mosquitoes has been confirmed in samples collected in July 2023 from wetlands near the River Idle in Nottinghamshire. This finding has only recently been reported following confirmatory testing and analysis. While notable, the current risk to horses and humans in the UK remains very low.
Key Clinical and Epidemiological Points:
• No equine or avian cases of WNV have been reported in the UK associated with local transmission. All confirmed equine cases to date have been linked to recent travel abroad.
•The presence of the virus in mosquito vectors highlights the importance of continued surveillance, particularly as climate conditions shift.
• Veterinary practitioners should include WNV in their differential diagnosis for acute neurological presentations, especially in horses exhibiting tremors or ataxia, even when travel history is unclear.
• Horse owners travelling to endemic regions with their horses should be advised to consider WNV vaccination, especially during mosquito season.
• Seasonality may no longer be a reliable predictor of mosquito activity. Climate change has increased the complexity and unpredictability of vector-borne disease patterns.
While this is the first known detection of WNV in UK mosquitoes, there is currently no cause for alarm. BEVA supports proactive awareness and preparedness in equine practice, including:
• Maintaining diagnostic vigilance in cases of neurological disease;
• Supporting education regarding vector-borne risks when travelling;
• Ecouraging the integration of vector awareness into regional disease surveillance planning.
We will continue to monitor any further developments and share relevant updates with our members and the wider equine community.
Find further resources on WNV and neurological disease in horses here.
Prof James Wood, Infectious Disease Epidemiologist at the University of Cambridge and Co-Director of Cambridge Infectious Diseases, University of Cambridge and BEVA Board member, said:
“It is very interesting that UKHSA and APHA have published evidence of WNV infection in mosquitoes in England, although it is not especially surprising as it has been known for some time that previously infected migratory bird species have been travelling to and in some cases then spending summers in the UK. WNV has become more prominent across Europe over the last 10-20 years. Risk mapping has identified parts of England, in particular in the South, as sites where WNV transmission might be expected. It is not clear whether this finding is simply a new observation of something that has been occurring for years, or a new occurrence. APHA has monitored dead birds for WNV for some time, but not detected it and while this surveillance is to be applauded, surveillance in healthy wild birds has never been undertaken. Flaviruses such as WNV, more generally often do not cause disease in their avian hosts. The natural cycle for transmission for many of these does not involve mammalian hosts, but spillover into horses and humans, with clinical disease consequences is known as a concern for WNV when it does happen. Encephalitis is seen occasionally in both humans and horses.
“Veterinary and public health authorities have known for some time about the risks of WNV transmitting to humans and horses and this new finding does emphasise the importance of medical and veterinary surveillance in cases of unexplained encephalitis. When WNV is known to be circulating locally, then enhanced mosquito avoidance approaches (stabling of horses, especially at dawn and dusk in high risk areas) may be warranted.”