Tick-borne Encephalitis: Causes and How It Spreads

Key points

  • Tick-borne encephalitis is caused by a virus primarily spread to people through the bite of an infected tick.
  • Tick-borne encephalitis virus is maintained in the environment between ticks and animals.
  • Human do not spread the infection other than rarely through blood transfusion, organ transplantation, and breastfeeding.
Ixodes scapularis tick crawling on a stick

Primary cause

Tick-borne encephalitis is caused by a virus that is found in parts of the region stretching from western and northern Europe to northern and eastern Asia.

There are three different subtypes of tick-borne encephalitis virus, namely European, Far Eastern, and Siberian. They are found in different areas and cause disease of varying severity.

How it spreads

  • TBE virus is spread to people primarily through the bite of an infected Ixodes tick.
  • Ticks become infected when they feed on small rodents that have the virus in their blood.
  • People do not develop high enough levels of the virus in their blood to infect biting ticks. As a result, people are considered "dead-end" hosts for TBE virus.
  • People can also be infected by consuming unpasteurized milk or cheese from infected goats, sheep, or cows, through slaughtering of infected animals, or from exposure to the virus in the laboratory.
  • The virus is not transmitted from person-to-person, except rarely by blood transfusion, organ transplantation, or breastfeeding.
    • Because the virus can be transmitted through blood, persons who were recently diagnosed with TBE virus infection should not donate blood or bone marrow for 120 days following infection.
  • Prevent getting sick with TBE virus by preventing tick bites or getting vaccinated, if appropriate for you based on your travel plans.