Hikers and mountain bikers have been urged to protect themselves after health officials confirmed that a potentially deadly virus spread by ticks is present in the UK. The first confirmed domestically acquired case of tick-borne encephalitis virus (TBEV) was identified in a 50-year-old man who was bitten by ticks while mountain biking in Yorkshire. The virus has also been detected in Hampshire, Dorset and Norfolk and it may also be present elsewhere, officials said, as the tick species that carries the virus is widespread in the UK. Another probable case in a person has been detected in the Loch Earn area of Scotland. TBEV is a virus carried by ticks and is common in many parts of the world, including in Europe. It causes a range of disease, from completely asymptomatic infection or mild flu-like illness to severe infection in the central nervous system such as meningitis or encephalitis. Encephalitis is an uncommon but serious condition in which the brain becomes swollen. It can be life-threatening and requires urgent treatment in hospital. Anyone can be affected, but very young and very old people are most at risk. Officials stressed that the risk to the public was very low, however. There have been three cases of probable or confirmed TBEV acquired in England since 2019, according to officials, including the Yorkshire case in 2022, which was the first confirmed case in the UK. “Although the risk to the general public is very low, it is important for people to take precautions to protect themselves from tick bites, such as covering their ankles and legs, applying insect repellent and checking clothes and your body for ticks, particularly when visiting areas with long grass such as woods, moorlands and parks,” said Dr Helen Callaby, of the UK Health Security Agency. Research led by Callaby and her colleagues at the Rare and Imported Pathogens Laboratory in Porton Down confirmed that TBEV was now present in the UK. The research is being presented this week at the European Congress of Clinical Microbiology and Infectious Diseases (ECCMID) in Copenhagen, Denmark. The diagnosis was first considered by doctors treating the patients and was confirmed by testing at the UKHSA laboratory. “This study confirms the tick-borne encephalitis virus is present in parts of the UK where there are relevant tick and wildlife populations and may occasionally cause disease in humans,” Callaby said. “Physicians should consider the possibility of tick-borne encephalitis virus when patients present with unexplained encephalitis and a history of tick exposure, even if they have not travelled outside the UK, as the clinicians did in these cases.” Investigations into why the virus has been found in ticks more frequently in recent years are under way, and there are likely to be a number of factors. UKHSA has recommended changes to testing in hospital so that any further cases can be detected promptly, and it will be enhancing surveillance, including asymptomatic surveillance in people in the Yorkshire area. The 50-year-old man presented with fatigue, muscle pain and fever five days after being bitten by a tick while mountain biking in a forest in Yorkshire. After initially recovering, his fever returned a week later with a headache and loss of coordination. MRI scans showed changes in keeping with viral encephalitis. Ticks can carry other diseases, such as Lyme disease, a bacterial infection that can be treated with antibiotics, so UKHSA is reminding the public to check themselves for ticks after they have been outdoors and remove them promptly and correctly if they are found. Dr Meera Chand, a deputy director at UKHSA, said: “Our surveillance suggests that tick-borne encephalitis virus is very uncommon in the UK and that the risk to the general population is very low. Ticks also carry various other infections, including Lyme disease, so take steps to reduce your chances of being bitten when outdoors in areas where ticks thrive, such as moorlands and woodlands, and remember to check for ticks and remove them promptly.”