Tick-Borne Encephalitis

Ron Smith, MD

Quick Overview

Tick-Borne Encephalitis

(content attributions: WHO, WHO, Encephalitis Society)


Tick-borne encephalitis (TBE) is an important cause of viral infections of the central nervous system in eastern, central, northern and increasingly western European countries, and in northern China, Mongolia, and the Russian Federation. Tick-borne encephalitis virus is a member of the family Flaviviridae. Approximately 10 000–12 000 clinical cases of tick-borne encephalitis are reported each year, but this figure is believed to be significantly lower than the actual total number of clinical cases.

The vast majority of infections with the virus result from infected ticks, which often remain firmly attached to the skin for days. On rare occasions, infection can result from consumption of unpasteurized milk from infect goats, sheep or cows. People come in contact with the ticks during outdoor activities in forested areas up to an altitude of about 2000 meters. There is no direct person-to-person transmission.

What are the symptoms of TBE?

Most infections remain asymptomatic. In case of clinical illness, the incubation period for tick-borne encephalitis lasts 2–28 days (most commonly 7–14 days) and is followed by 1–8 days of general cold symptoms, such as fatigue, headache and general malaise, usually combined with fever of ≥38 °C.

After an asymptomatic interval of 1–20 days up to 15% of patients experience a second phase of the disease characterized by fever frequently exceeding 40 °C and signs of central nervous system involvement, such as meningitis (e.g. fever, headache, and a stiff neck), encephalitis (e.g., drowsiness, confusion, and sensory disturbances), myelitis or radiculitis.

Encephalitis developing during this second phase may result in paralysis, permanent sequelae or death. About 1% of cases with neurological pathologies may die; higher fatality rates have been reported from the Russian federation, which may be related to a different virus subtype. Severity of illness increases with age of the patient, but fatalities have been reported from all age groups.

In the European type of TBE there are normally two phases to the illness. The first phase consists of flu-like illness with symptoms such as fever, headache and generalised body aches. It lasts around five days. There is then about a week with no symptoms, which is followed by the second phase of the illness, when the brain or nerves are involved. The severity of the second phase varies between patients. Some people have a very mild illness whilst others may have a severe illness. Older people tend to get a more severe illness than younger people or children.

The symptoms in the second stage are similar to other causes of encephalitis and meningitis (inflammation of the lining of the brain). These include neck stiffness, headache, nausea, impaired consciousness (from drowsiness to coma), poor coordination, tremor, personality changes and psychosis. Some patients will also get muscle pain or limb weakness (most often in the arms). In severe cases the muscles that control the breathing are affected and people may die.

How is it diagnosed?

TBE can be diagnosed by a blood test and lumbar puncture (LP). LP (sometimes called a ‘spinal tap’) is a procedure which involves passing a needle, under local anaesthetic, between two of the backbones at the base of your spine to collect the cerebrospinal fluid (CSF) (fluid surrounding the brain and the spinal cord).

The virus can be detected in the blood in the first phase of the illness, whilst the antibodies can be found in blood and cerebrospinal fluid, usually, in the second phase. Brain scans such as CT (computed tomography) and MRI (magnetic resonance imaging) can show abnormalities specific encephalitis, but do not have specific characteristics for TBE.

Treatment of TBE?

Unfortunately, there is no specific treatment for TBE. For people who have severe disease they may need supportive treatment in hospital such as intensive care. However, most people will only need symptom control.

Consequences of TBE

Some people (less than 2%) may die from TBE. This is more common in the Far-Eastern type. Some people will recover completely. Still others may have long lasting problems such as paralysis (the inability to move your arms and/or legs), ataxia (difficulties with coordination, balance and speech), headache, tiredness, difficulty concentrating and poor memory. If children are affected, they may be left with long-term cognitive problems such as short-term memory, headache, fatigue and irritability.

Prevention of TBE

People can protect themselves from ticks by wearing appropriate clothing, including long trousers and closed footwear, when hiking or camping in countries or areas at risk. The whole body should be inspected daily and attached ticks removed as soon as possible. The consumption of unpasteurized dairy products should also be avoided in those areas.

In a new position paper, published in the Weekly Epidemiological Record today, WHO recommends vaccination against tick-borne encephalitis in people of all ages where the disease is highly endemic. Where the prevaccination incidence of the disease is moderate or low or is limited to particular geographical locations or certain outdoor activities, immunization should target individuals in the most severely affected groups. People travelling from non-endemic areas to endemic areas should be offered vaccination if their visits will include extensive outdoor activities.

Since the incidence of tick-borne encephalitis may vary considerably between and even within geographical regions, public immunization strategies should be based on risk assessments conducted at country, regional or district level, and should be appropriate to the local endemic situation.

Immunization offers the most effective protection against tick-borne encephalitis. Currently, there are four widely used vaccines of assured quality: FSME-Immun and Encepur, manufactured in Austria and Germany respectively, and TBE-Moscow and EnceVir, manufactured in the Russian Federation. The four vaccines are considered to be safe and efficacious.



Table of Country Specific Risks (CDC)

TBE virus transmission can vary within a risk area from year to year.

Risk Information
Focally endemic throughout country. Highly endemic regions include Burgenland, Carinthia, Styria, Tyrol, and Vorarlberg States.
Almost all of the country considered endemic; no TBE virus detected in some small geographically dispersed areas.
Almost all of the country considered endemic; no TBE virus detected in some small geographically dispersed areas.
Bosnia and Herzegovina
Situation is unclear as very limited information is available. Fewer than 10 human cases reported. TBE virus previously isolated from ticks.
Cases only reported sporadically, but extent of underdiagnosis is unknown.
About 90% of cases reported from northeastern China, with highest endemicity in Inner Mongolia Autonomous Region (Daxing’an Mountains), Heilongjiang Province (Xiaoxing’an Mountains), and Jilin Province (Changbai Mountains). Northwestern China in the Xinjiang Autonomous Region (Tianshan and Altai Mountains) and southwestern China in Yunnan and Tibet provinces also reported to have transmission. One U.S. traveler also previously infected in Tianjin Province.
Highest risk reported in northeastern and northwestern regions, with lower risk in central mountainous region and only sporadic cases reported from Adriatic coastal region. Most cases reported from Koprivnica-Krizevci, Medimurje, and Bjelovar-Bilogora counties
Czech Republic (Czechia)
Highly endemic and regularly among countries with highest reported incidence in Europe. Foci of transmission occur throughout country, with greatest risk reported from Southern Bohemian Region.
Endemic only on Bornholm, an island in the Baltic Sea. Very rare sporadic cases reported from other areas including from microfoci in North Zealand.
Only two probable human cases ever reported (in 2019 and 2020). Both cases likely infected in focal area in New Forest /Hampshire, and infected ticks also identified in nearby area. TBE virus-infected ticks also identified in Thetford Forest, East Anglia. United Kingdom health authorities do not have recommendations for vaccination of the local population.
Highly endemic and regularly among countries with highest reported incidence in Europe. Endemic areas found throughout the country, with highest incidence in western part of country.
Based on local vaccination recommendations, the greatest risk is for persons resident during the transmission season in the Åland Islands, Pargas, Simo, southern parts of Kemi, the Kotka Archipelago, the Sammonlahti district of Lappeenranta, on the island of Preiskari close to Raahe, the Lohjanjärvi archipelago area, Kustavi, Luoma area in Kirkkonummi, and in part of the Sipoo archipelago (as of March 2021).
Main endemic area is Alsace in the northeast. In small number of additional locations mostly sporadic cases occur. French health authorities do not have recommendations for vaccination of the local population.
Highest risk in southern part of Germany, with 80% to 90% cases reported from Baden-Wurttemberg and Bavaria. Other key risk areas include southern Hesse, southeastern Thuringia, and Saxony. Additional localized areas of risk are in central Hesse, Saarland, Rhineland-Palatinate, Lower Saxony, and Saxony-Anhalt.
Highest incidence in the western (Transdanubian) and northern parts of country with much lower risk in most other areas.
Risk primarily in the pre-alpine and alpine areas in the northeast including Veneto (mainly Belluno alps), Friuli-Venezia Giulia, and Trentino-South Tyrol also referred to as Trentino-Alto Adige (Bolanzo and Trento provinces) regions.
Fewer than 10 TBE cases diagnosed during past 30 years, all in Hokkaido prefecture (island in northern Japan). Japanese health authorities do not have recommendations for vaccination of the local population.
Main risk areas considered to be Almaty and East Kazakhstan regions, and the Sandyktau district of Akmola region. Rare sporadic cases reported from some other central and northern locations.
Situation is unclear as very limited information is available. TBE virus-infected ticks and possible human case reported from Ala-Archa National Nature Park in Tian Shan mountains (Chüy Region).
Highly endemic and regularly among countries with highest reported incidence in Europe. Endemic areas are present throughout the country, with highest incidence in Kurzeme region in west and Vidzeme and Riga regions in central Latvia.
TBE virus-infected ticks previously detected. Liechtenstein health authorities consider risk exists in entire country.
Highly endemic and regularly among countries with highest reported incidence in Europe. Endemic areas present throughout country, with highest incidence in recent years in Utena County.
Situation is unclear as very limited information is available. TBE virus previously isolated from ticks.
Main risk area in Selenge and Bulgan provinces in the north.
First human cases identified in 2016, with sporadic cases from several different locations diagnosed since. Dutch health authorities do not have vaccination recommendations for local population.
Coastal areas in southern Norway, specifically Agder and Vestfold and (og) Telemark Counties, considered endemic.
Greater than 70% of reported cases diagnosed in Podlaskie and Warmian-Masurian provinces in northeast. Most of remainder of country has endemic foci.
Only sporadic cases reported, but information limited and disease might be underdiagnosed.
Endemic areas widespread across southern part of the non-tropical forest belt and variable incidence in different locations. As of 2019, 48 regions considered endemic. High transmission reported from southern parts of Western and Eastern Siberia and Southern Urals.
Low number of reported cases, but diagnostic testing not routinely conducted; cases reported from various locations including rural areas in the vicinity of Belgrade.
Foci of transmission distributed throughout the country with higher risk areas in north and center, particularly Banská Bystrica, Žilina, and Trenčín regions.
Highly endemic and regularly among countries with highest reported incidence in Europe. Cases reported from throughout the country with highest incidence in north and central regions.
South Korea
No human cases reported; TBE virus detection in ticks and rodents only. South Korean health authorities do not have recommendations for vaccination of the local population.
Highly endemic in regions around Stockholm in the eastern part of south-central Sweden (Stockholm Archipelago, Malaren Lake, Uppsala and Sodermanland counties), with other main risk areas around lakes (i.e., Vanern, Vattern) in the south. There are other natural foci in southern and central parts of country.
Entire country, except for cantons of Geneva and Ticino, considered at-risk. Higher risk in north-eastern, central, and midwestern regions of the country, with Thurgau canton considered highly endemic.
TBE viral ribonucleic acid detected in one pool of ticks from northwestern Tunisia but local establishment of TBE virus not confirmed.
Majority of infections during last 15 years reported from the Volyn region and Crimea. Other TBE foci detected throughout the country, including in the Rivne, Zhytomyr, Kyiv, Chernihiv and Carpathian regions.