Guidance

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 infectious disease that attacks the central nervous system and can result in long-term neurological symptoms, and even death. TBE virus (TBEV) is a member of the genus Flavivirus.

Epidemiology

TBEV has 3 subtypes, which are closely related:

  • European, transmitted by Ixodes ricinus ticks, and endemic in rural and forested areas of central, eastern and northern Europe

  • Far-Eastern, transmitted mainly by Ixodes persulcatus, and endemic in far-eastern Russia and in forested regions of China and Japan

  • Siberian, transmitted by Ixodes persulcatus, and endemic in Urals region, Siberia and far-eastern Russia, and some areas in north-eastern Europe

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 is also, but more rarely, associated with consumption of unpasteurised milk or milk products from infected animals.

TBEV is not directly transmitted from person to person, but is rarely transmitted through transplants, blood transfusion and breastfeeding. Infection has also followed laboratory incidents.

Symptoms

The incubation period of TBE is 7 days on average, but periods of up to 28 days have been described. The incubation period after foodborne infection is usually shorter, around 4 days.

Approximately two-thirds of human TBE virus infections are asymptomatic. In clinical cases, TBE often has a biphasic course. The first viraemic phase lasts approximately 5 (range 2–10) days, and is associated with non-specific symptoms (fever, fatigue, headache, myalgia, nausea).

This phase is followed by an asymptomatic interval lasting 7 (range 1 to 33) days that precedes the second phase, when the central nervous system is involved. 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, mortality rates of 0.5 to 2%, and severe neurological sequelae in up to 10% of patients. In children, the second phase of illness is usually limited to meningitis, whereas adults older than 40 years are at increased risk of developing encephalitis. There is a higher mortality and longer-lasting sequelae in those over the age of 60 years.

Acute encephalitis of any cause is a notifiable disease and should be notified to Public Health England if suspected.

Anyone with flu-like symptoms following a tick bite should visit their GP or call NHS 111.

Laboratory diagnosis

Testing can be arranged with the PHE Rare and Imported Pathogens Laboratory (RIPL). If TBE is suspected, the referring clinician should contact a clinician at RIPL to discuss the case.

Rare and imported pathogens laboratory (RIPL)

Public Health England
Manor Farm Road
Porton Down
Wiltshire
SP4 0JG

TBEV is a notifiable organism, and you should notify Public Health England 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 where the incidence varies considerably, with highest rates reported from Lithuania, Latvia and Estonia.

Ticks carrying the virus are also found in France, Germany, Italy, Scandinavia, Greece and Switzerland.

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 GP or travel clinic for more information.

Consider having a course of vaccine before you travel and always practice 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. 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 is considered to be a highly probable case of tick borne encephalitis. 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 those who may be bitten by ticks while visiting, living or working in areas where infected ticks have been located.

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

For further information, see NaTHNaC factsheet.

Published 6 August 2019