Tick-borne encephalitis: epidemiology, diagnosis and prevention
Advice for health professionals on tick-borne encephalitis (TBE) including symptoms, diagnosis and epidemiology.
Tick-borne encephalitis (TBE) is a viral infection that causes minimal or no symptoms in the majority of people. In rare cases, the virus can attack the central nervous system and can result in long-term neurological symptoms or (very rarely) death. TBE virus (TBEV) is a member of the genus Flavivirus.
Epidemiology
TBEV has 5 main subtypes, which are closely related:
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European, transmitted by Ixodes ricinus ticks, and endemic in rural and forested areas of central, eastern and northern Europe
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Far-Eastern, transmitted mainly by Ixodes persulcatus, and endemic in far-eastern Russia and in forested regions of China and Japan
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Siberian, transmitted by Ixodes persulcatus, and endemic in Urals region, Siberia and far-eastern Russia, and some areas in north-eastern Europe
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the recently recognised Baikalian subtype, transmitted by Ixodes persulcatus, and found in East Siberia
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the recently recognised Himalayan subtype, for which Marmota himalayana is the primary host, and found in the Qinghai-Tibet Plateau in China
The European subtype is associated with milder disease.
See Ixodes ricinus distribution map.
See Ixodes persulcatus distribution map.
Competent reservoir hosts of TBEV are mainly small rodents (voles, mice) and insectivores (shrews). Other animals support virus circulation indirectly by enabling tick multiplication. These include wild and domestic mammals, especially hares, deer, wild boar, sheep, cattle and goats.
Transmission
TBEV is normally transmitted by the bite of an infected tick.
In humans, disease can also be acquired by consumption of unpasteurised milk or milk products from infected animals, although this is very rare.
TBEV is not directly transmitted from person to person. There have been case reports of transmission through organ transplants, blood transfusion, via the transplacental route and breastfeeding. Infection has also followed laboratory sharps injuries.
Symptoms
The average incubation period of TBE is 7 days, but may be up to 28 days. The incubation period for foodborne infection is usually shorter, around 4 days.
Approximately two-thirds of human TBE virus infections are asymptomatic. In symptomatic cases, it is often biphasic, with an initial viraemic phase lasting approximately 5 days (range 2 to 10), and is associated with non-specific symptoms (fever, fatigue, headache, myalgia, nausea).
This phase is usually followed by an asymptomatic interval and apparent recovery, lasting 7 days (range 1 to 33). The second phase begins approximately 7 days after initial resolution of symptoms (range 1 to 33 days) and involves the central nervous system. Typical presentations are meningitis, meningoencephalitis, myelitis, paralysis, or radiculitis.
The European subtype is associated with milder disease, with 20 to 30% of patients experiencing the second phase, severe neurological sequelae in up to 10% of patients, and an overall mortality of 0.5 to 2%. In children, the second phase of illness is usually limited to meningitis, while adults older than 40 years are at increased risk of developing encephalitis. There is a higher likelihood of long-lasting sequelae, and a higher mortality, in those over the age of 60 years, the immunocompromised, or those with significant co-morbidities.
Acute encephalitis of any cause is a notifiable disease and should be notified to the UK Health Security Agency (UKHSA) if suspected.
Anyone with flu-like symptoms following a tick bite should contact their GP or call NHS 111.
Laboratory diagnosis
Testing is done by the UKHSA Rare and imported pathogens laboratory (RIPL). If TBE is suspected, the referring clinician should contact a clinician at RIPL to discuss the case to ensure that the correct samples are sent for testing.
Rare and imported pathogens laboratory (RIPL)
UK Health Security Agency
Manor Farm Road
Porton Down
Wiltshire
SP4 0JG
Email ripl@ukhsa.gov.uk
Telephone 01980 612348 (available 9am to 5pm, Monday to Friday)
DX address DX 6930400, Salisbury 92 SP
TBEV is a notifiable organism, and you should notify your local health protection team if detected.
Risks for UK travellers
If you are travelling outside the UK, check whether you are visiting a place where TBE is present. TBEV-Eur is endemic in rural and forested areas of central, eastern and northern Europe. The incidence varies considerably, with highest rates reported from Lithuania, Latvia, Estonia, Slovenia and Czechia.
Ticks carrying the virus can be found in many parts of Europe and Asia.
Check whether you are visiting a place where TBE is present. You can look up the country you’re visiting on the TravelHealthPro country information pages, or speak to a travel clinic for more information.
Consider having a course of vaccine against TBEV before you travel. You can get more information on the TBEV vaccine from a travel clinic, or from your GP practice if it provides a travel vaccination service. Always practise tick avoidance.
Risk in the UK
In 2019, TBEV (European subtype) was detected in a small number of ticks in Thetford Forest and an area on the border between Hampshire and Dorset. Subsequently, TBEV-positive ticks have been found in North Yorkshire. Further work is under way to identify the distribution of TBEV-infected tick populations in England.
In July 2019, a European visitor became ill after being bitten by a tick in the New Forest area. This was considered to be a highly probable case of tick-borne encephalitis, based on serological testing.
In July 2020, a second probable case of TBE infection was diagnosed in a patient from Hampshire, again based on serological testing.
In September 2022, a third case, confirmed positive by polymerase chain reaction (PCR), was diagnosed in an individual who is likely to have acquired infection in the Loch Earn area of Scotland.
In October 2022, a fourth case, also confirmed positive by PCR, was diagnosed in an individual who reported recent exposure to ticks in the North Yorkshire Moors in England.
To date, all other cases of TBEV infection reported in the UK have been acquired through travel to high-risk areas abroad.
The risk from TBEV is currently assessed as very low for the general public, and low for high-risk groups (such as those living, working or visiting affected areas).
Lyme disease remains the most commonly acquired tick-borne infection acquired in the UK and it is important to be tick aware when spending time outdoors.
Tick resources and surveillance
Tick toolkits and tick awareness materials
Iinformation on how to take part in the tick surveillance scheme
For further information, see NaTHNaC factsheet.
Last updated 25 April 2023 + show all updates
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Updated to include latest epidemiological and case information. Added further detail on the clinical aspects of tick-borne encephalitis.
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First published.