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Tick-borne Encephalitis Confirmed in England

Health officials confirmed that tick-borne encephalitis virus (TBEV) was now likely to be present in England after assessing human cases and detection of the virus in ticks in several areas of the country. 

The UK Health Security Agency (UKHSA) said that a case of TBEV last year likely to have been acquired in the Yorkshire area had been confirmed as the first known case in England. Public Health Scotland joined colleagues in England in warning the public to be 'tick aware' after reporting that a probable human case of TBEV was likely to have been acquired in central Scotland in 2022.

An ongoing investigation coordinated by the UKHSA and the Department for Environment, Food and Rural Affairs also confirmed that the virus has been detected around the border of Hampshire and Dorset and in Norfolk.

TBE is caused by the Flavivirus genus. Around two-thirds of patients are asymptomatic. For those who develop symptoms, there are often two phases. The first is associated with influenza-like symptoms, including fever, headache, and fatigue. In a small number of cases this can lead to a more serious second phase that involves the central nervous system, potentially leading to meningitis, encephalitis, and paralysis.

Dr Meera Chand, deputy director at the 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."

Details of the First Case

The case from Yorkshire involved a 50-year-old man who sought medical attention after experiencing fatigue, myalgia, and fever 5 days after sustaining a tick bite while mountain biking in a forest in Yorkshire. Details of the case, along with those of a 28-year-old man who presented with extreme fatigue after removing several ticks from his ankles during a hiking trip to Loch Earn in Scotland in June last year, were outlined in a UKHSA presentation to the European Congress of Clinical Microbiology and Infectious Diseases held in Copenhagen this month. In total, 18 cases with either positive molecular or serological testing were identified as having been acquired in the UK between 2015 and 2022.

Study author Dr Helen Callaby from the UKHSA Rare and Imported Pathogens Laboratory, Porton Down, said: "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."

Recommended Changes to Hospital Testing

In its new risk assessment, the Agency said it was recommending changes to hospital testing so that any further cases could be detected promptly. Enhanced surveillance would also include asymptomatic surveillance in people in the Yorkshire area.

As ticks can carry other diseases, including Lyme disease, health officials renewed advice for the public to take precautions. Dr Chand said people should "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".

Scientists had suspected the virus was present in the UK in 2019 after sampling ticks in Thetford Forest. During the same year, a 3-month-old baby from Germany was thought to have been infected with TBEV while on a family holiday in the New Forest.

Further Surveillance Measures

Experts were still seeking to establish why TBEV had become more prevalent in recent years but said it was likely because of "a number of factors". The UKHSA carries out surveillance of vector-borne diseases in the UK to understand more about emerging infections. In a comment to the Science Media Centre, Sally Cutler, professor of medical microbiology at the University of East London, suggested this could be due to "multi-factorial human influences such as climate change, land fragmentation, and behavioural influences".

Roman Biek, professor of disease ecology and molecular epidemiology at the University of Glasgow, said: "These human cases are not a surprise – ticks infected with the virus had been detected in the UK in recent years and there had been suspected cases. What is unexpected, are the locations of these human cases, as they occurred at some distance from where the virus had been found previously. This indicates that the virus is more widely distributed in the UK than we had anticipated."

Ian Jones, professor of virology at the University of Reading, assessed that it was "unlikely that TBEV will disappear, but the general threat level is very low and there is no reason to suppose cases in people will be any more than sporadic in nature".