The UK Health Security Agency (UKHSA) has warned the public to avoid ticks after links were found between the bugs and cases of brain disease in four areas of the UK.
Since 2019, four cases of possible or confirmed tick-borne encephalitis (TBE) have been identified in Britain, including two last year.
TBE is endemic in rural and forested areas of central, eastern, and northern Europe and some Eurasian areas, but it was not found in the UK before 2019.
At least two strains of the TBE virus have since been found in ticks and deer in four areas in England.
Virus-carrying ticks were found in Thetford Forest in the east of England, the Hampshire and Dorset border, the New Forest in southern England, and the North Yorkshire Moors, the UKHSA said.
Of the four human TBE cases, the first possible case was identified in July 2019, when a European visitor became ill after being bitten by a tick in the New Forest, Hampshire. The patient was diagnosed as a highly probable case of TBE.
In July 2020, a second probable case of TBE infection was diagnosed in a patient from Hampshire, the agency said.
In September and October 2022, two patients tested positive for the TBE virus by polymerase chain reaction (PCR) testing, including one that may have been infected in Scotland in June 2022.
The fourth patient was likely exposed to the virus at the North Yorkshire Moors, according to the UKHSA.
Humans can contract the disease by being bitten by ticks, but some cases have been associated with consumption of unpasteurised milk or milk products from infected animals, the UKHSA said.
Transmission from mother to foetus has been found during animal studies, but human to human transmission via transplant, blood transfusion, or breastfeeding are rare.
Most Infections Are Mild
Most of those who are infected by the TBE virus may experience flu-like illness or not show any symptoms at all, the UKHSA said. But some can suffer severe infection in the central nervous system such as meningitis or encephalitis, with symptoms including a high fever with headache, neck stiffness, confusion, or reduced consciousness.Severe illness is more likely to occur in adults, particularly in the elderly.
Of the 3,029 cases in which outcomes were known, 16 deaths were reported, representing a case fatality rate of 0.5 percent.
The UKHSA said it’s possible that the virus was brought into the UK by migratory birds or movements of other animals, including pets.
The assessment also said the disease may already be endemic in ticks in high risk areas in the UK, but the quality of evidence is poor.
The UKHSA recommended that local awareness should be raised on tick avoidance measures for the public and clinicians in known affected areas.
Dr. Meera Chand, deputy director at UKHSA, said in a statement: “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.
The UKHSA said NHS staff should consider testing for TBE virus when a meningitis patient has had forest exposure or tick bites, or when there’s no clear alternative diagnosis but compatible illness.
The agency recommended testing of human and deer blood serums, including among higher risk groups such as forestry workers or hikers, to understand background seropositivity.
They also recommended research into fresh unpasteurised milk from an infected animal and the effects of cheese production processes on the quantity of infectious virus present.
