Ticks, specifically hard ticks of the family Ixodidae, act as both the vector and reservoir for TBEV. The main hosts are small rodents, with humans being accidental hosts. Large animals serve as feeding hosts for the ticks, but do not play a role in maintenance of the virus.
The virus can chronically infect ticks and is transmitted both transtadially (from larva to nymph to adult ticks) and transovarially (from adult female tick to eggs). TBE cases occur in humans most frequently in rural areas and during the highest period of tick activity (between April and November). Infection also may follow consumption of raw milk from infected goats, sheep, or cows. Laboratory infections were common before the use of vaccines and availability of biosafety precautions to prevent exposure to infectious aerosols. Person-to-person transmission has not been reported with the exception of vertical transmission, from an infected mother to fetus.