West Nile Virus Identified in British Mosquito for the First Time

The West Nile virus, marking the first potential fatal mosquito-borne disease in the UK, has been identified for the first time.

The UK Health Security Agency (UKHSA) has announced that its research collaboration with the Animal and Plant Health Agency has Afa successfully identified a “fragment” of the virus in Aedes aegypti mosquitoes collected from the marshlands along the Idol River in Nottinghamshire in July 2023, indicating that these insects are carriers of pathogens.

According to Alanfolly from Apha, the virus was discovered somewhat by chance during routine testing by his team. He notes that further screenings will take place around that area later this year. Interestingly, Nottinghamshire typically does not fall into Afa’s primary testing regions, which are mostly centered in southern and eastern England, where warmer climates increase the likelihood of infections such as West Nile.

Humans and horses can become infected with the West Nile virus through mosquito bites. Approximately 20% of infected individuals exhibit symptoms such as fever, headaches, body aches, vomiting, and diarrhea. In rare instances, the virus can lead to severe inflammation of the brain and spinal cord, which can be fatal. Currently, there are no approved vaccines for humans.

UKHSA has reported the virus’s presence only in two mosquito samples, with no current evidence suggesting that humans or horses are infected in the UK. The organization’s assessment indicates a very low risk to the public, but healthcare professionals are advised to test encephalitis patients for unexplained causes.

“This is the first identification of the West Nile virus in British mosquitoes, though it doesn’t come as a surprise given the virus’s ongoing spread across Europe,” stated Meera Chand from UKHSA.

The West Nile virus has been increasingly observed in Africa, Europe, and North America. In Europe, recent years have seen its northern spread, reaching the Netherlands in 2020.

Factors contributing to the spread of the West Nile virus include elevated spring and summer temperatures, summer droughts, and milder winters, all of which are becoming more prevalent in Northern Europe. Although APHA has not detected the West Nile virus in mosquitoes or birds for 2024, the recent warm weather in the UK could change that. “We had an unusually warm May,” Folly noted. “If there is another case, we may see it in the coming weeks. This is just the beginning; more cases could follow.”

British researchers have been vigilant for the West Nile virus since 2020 when a related mosquito-borne virus (USUTU) was first found in London. The West Nile virus shares similar transmission characteristics with USUTU and requires comparable environmental conditions.

“I wouldn’t be surprised at all,” stated Matthew Baylis from the University of Liverpool. “I’ve been expecting this to happen every year. I believe that the West Nile virus will eventually be detected in the UK.”

He suggested that the virus likely arrived in the UK via birds and is probably circulating among various mosquito species in the region. However, he reassured that there is no immediate cause for alarm. “The risk remains low for most people. While a few horses are susceptible to West Nile disease, it’s quite rare,” he added.