West Nile virus found in UK mosquitos for first time

West Nile virus has been found in mosquitoes collected in the UK for the first time, the UK Health Security Agency (UKHSA) has said.

The virus, which mostly spreads to people through mosquito bites, can cause severe, life-threatening flu-like illness in about one in 150 people who are infected, according to the World Health Organization (WHO).

Mosquitoes pick up the virus from birds they bite and, in rare cases, can pass it on to people or horses.

Research by the UKHSA and the Animal and Plant Health Agency (APHA) has now detected the virus in fragments of Aedes vexans mosquitoes collected from wetlands on the River Idle near Retford, Nottinghamshire, in July 2023.

This is the first time West Nile virus has been found in mosquitoes in the UK.

No cases of local transmission to humans have been registered in Britain to date, and the UKHSA assessed the risk to the general public as "very low".

The agency said in a statement that, based on available surveillance, there was no evidence to suggest ongoing circulation of the virus in birds or mosquitoes in the UK.

Nevertheless, the UKHSA issued advice to healthcare professionals enabling them to test patients with encephalitis (swelling of the brain) of an unknown cause for West Nile virus as a precaution.

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It will also enhance disease surveillance and control activities in light of the findings.

"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 Meera Chand, UKHSA deputy director for travel health, zoonoses, emerging infections, respiratory and tuberculosis, said.

Dr Arran Folly, leading the project which detected the virus, said finding it in Britain was "part of a wider changing landscape, where, in the wake of climate change mosquito-borne diseases are expanding to new areas".

He said the Aedes vexans mosquito is native to the UK.

But warming temperatures could also bring non-native species capable of transmitting infectious diseases to humans into the country as they could find it easier to survive, reproduce and establish a local population here.

The main risk for contracting West Nile virus for UK residents is travel to endemic areas, which include Europe, Africa, the Middle East, West and Central Asia, North and South America, Australia and the US.

There have been seven travel-associated cases of the virus in the UK since 2000.

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