Tick-borne encephalitis

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.

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. There is no specific treatment for tick-borne encephalitis.

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.

Immunization offers the most effective protection. Currently, there are 4 widely used vaccines of assured quality: FSME-Immun and Encepur, manufactured in Austria and Germany respectively, and based on European strains of the virus; and TBE-Moscow and EnceVir, manufactured in the Russian Federation and based on Far-Eastern strains. The 4 vaccines are considered to be safe and effective.

In areas where the disease is highly endemic, WHO recommends that vaccination be offered to all age groups, including children.

Ticks also transmit Borreliosis (Lyme disease), which is a bacterial infection. TBE vaccination is not effective against this disease, which however is treatable with antimicrobials.