Tick-borne encephalitis is a disease caused by a virus, which is transmitted when bitten by a tick. In Europe, ticks involved in transmission are mainly of the genus Ixodes, which are found in shaded areas covered with thick litter or densely invaded by brush, ferns, and tall grasses. Small rodents are the natural reservoir of the virus.

Transmission of the virus is also possible through ingestion of unpasteurized milk and milk products from infected cattle, sheep and goats.

In about two thirds of cases, infection in humans will not cause symptoms and will therefore go unnoticed. When the disease develops, two symptomatic phases are usually separated by a symptom-free period: one phase of influenza syndrome and another characterized by damage to the central nervous system (meningoencephalitis). In this case, the disease can be severe, with a mortality rate of 0.5% to 2%.

The risk of infection varies according to the seasons and is highest from June to October, i.e. during the period of tick activity.

The disease is present in Asia and Europe, with a higher risk in Central Europe (Austria, Switzerland, Germany) and in Eastern Europe (Czech Republic, Hungary, Poland, etc.), in the Baltic republics (Estonia, Latvia, Lithuania), as well as in certain regions in Sweden and Finland. In Belgium, studies on animals (deer, wild boar, cows) have shown that the virus also circulates in Belgium. But to date, the disease has not been diagnosed in a person who has not traveled to an at-risk country.

There is a vaccine that is recommended in Belgium for people who travel to an area or country at risk and engage in outdoor activities (bivouacking, hiking, etc.).