The Chief Medical Officer’s Annual Report 2025 outlines the threat of tick-borne disease within the UK and considers how climate change could influence the risk.
The report confirms that Borrelia burgdorferi s.l., the causative agent of Lyme disease, is still the most common UK vector-borne disease. Approximately 1,500 laboratory confirmed cases in England and Wales are reported each year, plus 1,000 – 4,000 additional clinical cases. Further numbers may remain undiagnosed.
Tick-borne encephalitis virus (TBEV) has been found in UK ticks with 3 probable or confirmed cases between 2019 and April 2023. Ticks in the UK also carry other pathogens that could affect humans, including Louping ill virus, Babesia species, Anaplasma phagocytophilum, various Rickettsia species, as well as Spiroplasma.
Tick surveillance
The UKHSA’s Tick Surveillance Scheme has been recording tick distribution over the last 20 years. The UK has 20 tick species, several of which pose a risk to humans and some animals. The most common is the sheep or castor bean tick (Ixodes ricinus) which can transmit all of the pathogens listed above.
Sheep ticks occur throughout the UK, with distribution limited by microclimatic factors and the availability of animal hosts. Large areas of southern England, the North York Moors, Thetford Forest, Cumbria and North Wales are considered higher risk areas.
The distribution of roe deer and rough grazing with sheep and cattle are key factors in determining tick survival and are the primary drivers for change in distribution.
Climate change effects
Wetter and warmer weather will provide a more suitable habitat for ticks. Milder winters will lead to a shift in the seasonal tick activity, with extreme weather such as drought or floods potentially reducing their activity.
Infection rates in ticks
Infection rates in ticks vary geographically and year to year, depending on the weather, climate, and animal populations that help spread the bacteria. The effects of climate change are therefore indirect and complex.
Tree masting can impact small mammal populations, which are important in infecting ticks with Borrelia afzelii. Wild bird and gamebird populations, linked to Borrelia garinii, fluctuate naturally in response to weather and climate but can also be affected by human activity.
Over the last 10 years, average Borrelia infection rates in UK ticks have varied between 4% and 8%, with some recent evidence of an upward trend.
Tick-borne encephalitis virus
Tick-borne encephalitis virus currently appears in specific areas (primarily Thetford Forest in East Anglia, the Hampshire/Dorset border, the New Forest and the North Yorkshire Moors) but the overall risk to the public remains very low.
Warmer springs and milder winters, along with high deer numbers and coniferous woodland, are key factors influencing tick populations. Weather affects how ticks feed at different stages, and together with ecological factors, could influence how TBEV spreads.
Other non-native tick species
Other non-native tick species, such as Hyalomma marginatum (vector of Crimean Congo haemorrhagic fever virus) and Rhipicephalus sanguineus (vector of Rickettsia) are entering the UK on migratory birds and imported dogs. Both species will likely be able to survive in a warming UK climate.
Vaccination against tick-borne disease
A vaccine for Lyme disease is not currently available, although development is underway. However vaccination against Tick-borne encephalitis virus is available when paid for privately, for those at greater risk of exposure in the UK, or when travelling overseas. Read more about overseas regions at higher risk of TBE.
Planning for the future
Globally, climate change is already affecting health and infectious disease risk by influencing weather conditions. In the UK, changes are being seen in the distribution of many disease-carrying vectors.
Enhanced surveillance of vectors and the infections they carry will be needed, along with preparations for potential outbreaks of disease. Developing medical countermeasures, such as vaccines, could help manage the rising risk of infection.
For more information read the Chief Medical Officer’s Annual Report 2025 (see pages 338 – 343 of chapter 7, in the full report).