Tick-borne encephalitis emerges in Britain: Experts urge vigilance

By Dr. Chinta SidharthanReviewed by Susha Cheriyedath, M.Sc.Feb 10 2025

For the first time, scientists have confirmed tick-borne encephalitis in British patients with no travel history, proving that the virus is now spreading locally. What does this mean for public health—and how can you protect yourself?

Study: Tick-borne encephalitis: from tick surveillance to the first confirmed human cases, the United Kingdom, 2015 to 2023. Image Credit: Bukhta Yurii / Shutterstock

A disease once thought to be confined to mainland Europe has now made its way to the United Kingdom (U.K.). Tick-borne encephalitis (TBE), a virus spread through tick bites, has been confirmed in British patients. In a recent study published in the journal Eurosurveillance, a research team from the U.K. investigated the emergence of TBE in the nation, how it is diagnosed, and its public health implications.

Background

Ticks have long been known to transmit diseases such as Lyme disease, but another threat is emerging. Tick-borne encephalitis virus (TBEV) is a flavivirus that can cause severe neurological illness in humans. It has been endemic in parts of Europe and Asia for years, but the U.K. was hitherto not considered at risk. However, recent studies have identified TBEV in British wildlife and ticks, raising concerns about local transmission.

Most infections with TBEV cause no symptoms, but in some cases, the disease progresses to encephalitis, leading to brain inflammation, neurological damage, and, in rare cases, death. The study notes that in previous European cases, 0.5% of symptomatic TBE cases resulted in death, while 2.5% led to long-term neurological complications. Until recently, TBE cases in the U.K. were seen only in travelers returning from regions where the virus was endemic. However, the first probable U.K.-acquired cases were reported in 2019 and 2020, and with the virus now present in local tick populations, there is growing concern that the U.K. could see an increase in domestic cases of TBE.

About the study

The present study explored the first confirmed locally acquired human cases of TBE in the U.K. and their public health implications. The researchers conducted a retrospective analysis of TBE cases diagnosed between 2015 and 2023, focusing on identifying infections acquired within the country.

They reviewed the laboratory records from the U.K. Health Security Agency’s Rare and Imported Pathogens Laboratory, which conducts diagnostic testing for TBE. Based on clinical symptoms, polymerase chain reaction (PCR) testing, and antibody-based detection, cases were categorized as possible, probable, or confirmed.

Furthermore, surveillance was enhanced in 2022 after an increase in TBE cases was observed, and the study gathered clinical data from these surveillance records using structured case record forms from patients diagnosed in 2022 and 2023. Additional testing was performed to differentiate TBEV from the related louping ill virus (LIV), which is endemic in the U.K.

Intrathecal antibody production was also analyzed in cerebrospinal fluid samples to confirm central nervous system involvement. The researchers also attempted next-generation sequencing to characterize the virus strain in the U.K.-acquired cases, but the attempts were unsuccessful due to low viral loads. In addition to human case analysis, the study incorporated tick surveillance in suspected transmission areas to assess the prevalence of TBEV in U.K. tick populations, particularly in Thetford Forest (East of England), the Hampshire/Dorset border, Scotland (Loch Earn), and Yorkshire.

Major findings

The study confirmed the incidence of TBEV in the U.K. and reported that the virus had caused locally acquired human infections. The researchers identified 21 TBE cases between 2015 and 2023, including three possible, seven probable, and 11 confirmed cases. Of these, 12 cases were diagnosed in 2022–2023, comprising three possible, three probable, and six confirmed cases. Three cases had definite or highly probable U.K. acquisition—two confirmed and one possible—demonstrating that local transmission has occurred.

One patient contracted TBE after tick exposure in Scotland, while another was infected in Yorkshire. A third possible case with a definite U.K. acquisition was also identified. Both confirmed patients developed initial flu-like symptoms followed by neurological symptoms, including ataxia and confusion, but recovered with supportive care. Laboratory testing confirmed the presence of TBEV ribonucleic acid (RNA) or a significant rise in TBEV antibodies, ruling out other flavivirus infections. Surveillance efforts also confirmed TBEV in ticks collected from these locations, supporting evidence of an established enzootic cycle.

Furthermore, these findings highlighted the challenges of diagnosing TBE. Many TBE infections are asymptomatic or mild, and serological testing can be complicated by cross-reactivity with other flaviviruses. Cross-reactivity with Louping ill virus (LIV), which is endemic in the U.K., further complicates test interpretation, requiring additional PCR-based differentiation. Additionally, the presence of LIV in the U.K. complicates test interpretation. The researchers emphasized the need for increased clinician awareness, as many cases may go undiagnosed.

One key limitation of the study was the inability to perform whole genome sequencing due to low viral loads in patient samples. This prevented direct comparisons between U.K. and European TBEV strains. Nonetheless, the findings confirmed that TBEV is circulating in U.K. tick populations and can cause human disease.

Conclusions

Overall, the study provided the first definitive evidence of locally acquired TBE in the U.K., highlighting the need for increased surveillance and public awareness. Since 2023, testing for TBEV has been expanded to include all referred cases of unexplained encephalitis, regardless of travel history, marking a significant change in public health policy. The researchers believe that while the overall risk remains low, TBE should now be considered in cases of unexplained encephalitis, even in patients without recent travel.

Furthermore, public health efforts should include tick bite prevention education, with campaigns previously focused on Lyme disease now incorporating awareness of TBEV. Enhanced monitoring and expanded tick surveillance across larger regions of the U.K. are needed to better understand the spread of this emerging infection.