Transmission through ticks
Ticks are the chief carriers (vectors) and reservoir hosts of TBE virus in nature. The lack of digestive enzymes in the tick gut favours the survival of ingested microorganisms and may explain why ticks transmit a greater variety of pathogens than any other group of arthropods. Their ability to feed on the blood of a variety of host animals and to adapt to domestic animal species, as well as their long life cycle make them ideal vectors for a variety of pathogens (rickettsiae, spirochetes, other bacteria, fungi, protozoans, nematodes, viruses), among them the TBE virus.
The TBE virus can be transmitted to man or other hosts by larvae, nymphs, or adult ticks.
Other routes of transmission
Infection by the alimentary route as a result of the ingestion of raw milk is also possible and has been reported from Slovakia, Poland, and other Eastern countries. Recently the family outbreaks of TBE in Lithuania have reappeared. It is reported that in 2000 4% of TBE patients became infected via unboiled milk. Also, in Slovakia, goats and sheep play an important role in alimentary TBE infections. Since 1974, more than 50 cases of TBE occurred in Slovakia after the patients had eaten cheese made from raw sheep’s milk or drunk home produced raw goat or sheep milk.
Laboratory infections have likewise been reported. Although it has not been observed, man-to-man transmission is a theoretical possibility, e.g., when blood from a viremic patient is transfused to a healthy person.