The tickborne encephalitis virus is the causative agent of early summer meningoencephalitis (ESME), a tick-borne viral infection of the central nervous system.The European ESME occurs in western and central Europe (Germany, Austria, Swiss, Hungary, Czech Republic, Slovak Republic, former Yugoslavia, Poland, Baltic States, Russia and Scandinavia.The viruses are mainly transmitted by the bite of infected sheep tick (Ixodes ricinus), the most frequent hard tick species in central Europe. They use small mammals like hedgehogs, mice, moles etc. as host. A high number of infections are registered in the periods May-June and August-October. Transmission by non-pasteurized milk (cow's, sheep's and goat's milk) is possible but very rare.While sucking blood, ticks secrete large amounts of saliva, containing pathogens like the TBE virus. After inoculation to the skin and local replication, the virus reaches the regional lymph nodes, wherefrom it is spread in several extralymphatic organs (like connective, muscular and glandular tissue). After another replication phase the virus infects the brain (encephalitis), the membrane that surrounds the brain and spinal cord (meningitis) or both (meningoencephalitis).