The UK government has published a new contingency plan for West Nile virus (WNV) after mosquitoes carrying the potentially lethal disease were detected in the country. The virus claimed 67 lives across Europe in a 12-month period.
What Is West Nile Virus?
West Nile virus is a mosquito-borne illness typically spread through bites from infected Culex mosquitoes, which acquire the virus from birds. While 80% of infected individuals show no symptoms, about 20% develop mild flu-like illness. In rare cases (less than 1%), it can cause severe neurological diseases such as meningitis or encephalitis, which can be fatal.
Detection in the UK
Officials from the UK Health Security Agency (UKHSA) stated: "At the time of publication there have been no human cases of WNV acquired in the UK, but there have been detections of WNV in mosquitoes in the UK. The risk to the UK population is still considered to be very low, although increasing with climate change, particularly given the presence of WNV in neighbouring countries."
WNV was first detected in the West Nile district of Uganda in 1937. The first large outbreak in Europe occurred in Romania in 1996, and WNV is now endemic in parts of Europe. In 2002, WNV was declared endemic in the United States and has since spread into Canada and the Caribbean.
Transmission and Symptoms
Humans can become infected following a bite from an infected mosquito. Other transmission routes include from mother to unborn child, through breast milk, and via blood transfusions or organ transplants from infected donors, though these represent a small proportion of global infections.
Acute infection may cause fever, headache, muscle aches, and a rash. Although many infections are asymptomatic or mild, about 1 in 150 cases develop brain and nervous system disease, presenting as meningitis, encephalitis, or acute flaccid paralysis.
No Vaccine Available
The UKHSA warned there are no human vaccines available, so the policy is based on preventing infections. Guidelines instruct GPs across the UK to report any suspected cases immediately to the UKHSA.
High-Risk Groups
Those aged over 50 or with underlying medical conditions (such as cancer, diabetes, hypertension, and kidney disease) are at greatest risk of severe disease. The case fatality rate is highest in patients aged over 70.
Mosquito Distribution in the UK
The mosquito species that transmits the virus, Culex pipiens, occurs across the UK. It has been found on land adjoining the Thames estuary, as far north as Suffolk, in the Cambridgeshire Fens, and along the south coast in Sussex and Hampshire. Its distribution is expanding, likely in response to climate change.
Severe Symptoms
Severe symptoms may include high fever, severe headache, neck stiffness, confusion, coma, tremors, muscle weakness, vision problems, numbness, and paralysis. Older adults (especially those aged 55 and above) are at greater risk, with about 1 in 50 in this age group experiencing severe symptoms.
