A life-threatening tropical virus has been found in mosquitoes in Britain for the first time, which scientists attributed to climate change spreading the disease to cooler regions.
The UK Health Security Agency (UKHSA) detected fragments of the West Nile virus in mosquitoes collected from wetlands on the River Idle near Retford, Nottinghamshire.
The virus can cause flu-like symptoms and further dangers including coma. It is endemic across Africa, Asia and the Americas and in recent years has moved to parts of Europe.
The UKHSA said the risk to the public was “very low” and that the virus was not widely circulating. However, it has increased its surveillance efforts and is advising health workers to test patients with symptoms including brain swelling for the virus as a precaution.
As temperatures warm due to climate change, tick and mosquito species which are not native to Britain are increasingly able to survive here. Experts said we must prepare for more mosquito-borne diseases such as dengue fever, previously mainly confined to tropical countries, to spread to the UK.
West Nile virus is usually found in birds and circulates through bird-biting mosquitoes. In rare cases mosquitoes can transmit the virus to humans or horses. Symptoms include fever, headache and body aches and in some cases it can cause deadly complications affecting the nervous system and brain, such as meningitis or encaphelitis.
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The UKHSA said “fragments of West Nile virus genetic material” were found in some Aedes vexans mosquitoes in Nottinghamshire in July 2023. However, there is “no evidence to suggest ongoing circulation of the virus in birds or mosquitoes in the UK”.
Dr Meera Chand, of the UKHSA, said: “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.”
Dr Arran Folly, of the Animal and Plant Health Agency, added that mosquito-borne diseases were expanding to new areas “in the wake of climate change”.
It is possible that the virus entered Britain in mosquitoes, perhaps carried there on winds, or via a plane, train or car, Matthew Baylis, of the University of Liverpool, said. He added: “But it is much more likely that it was brought in by a migratory bird, which was then fed upon by mosquitoes.
“This should not be a major cause of concern. The spread of West Nile from southern Europe to northern Europe in the last few years has not led to a significant public health issue, although there have been cases in both humans and horses. I will not be surprised if we see a few cases in the UK too.
“There is a need to heighten surveillance, in humans, birds and mosquitoes. This is especially important given that severe cases that report or are reported to medical or veterinary authorities tend to be the tip of the iceberg, with many infected people or horses carrying the virus but not showing symptoms or signs.”
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Professor James Logan, from the London School of Hygiene and Tropical Medicine, said that the detection of the virus in the UK meant the “door is now open”.
“Whether the virus takes hold will depend on a combination of environmental, biological and human factors — including how well we prepare,” he said.
Professor Martin Hibberd, of the London School of Hygiene and Tropical Medicine, said: “With the likely arrival of West Nile virus into the UK, we also need to be prepared for the potential arrival of other viruses from the Flaviviridae family, such as the viruses that cause dengue.
“This research and surveillance should become part of a heightened preparedness to combat the effects of climate change.”