Where does encephalitis transmitted by ticks originate? - briefly
Tick‑borne encephalitis originates in forested areas of Europe and Asia where Ixodes ticks are endemic. The virus circulates among small mammals and reaches humans through tick bites.
Where does encephalitis transmitted by ticks originate? - in detail
Tick‑borne encephalitis virus (TBEV) circulates in natural foci where competent vectors and reservoir hosts coexist. Primary vectors are hard ticks of the genus Ixodes, principally Ixodes ricinus in Central and Western Europe and Ixodes persulcatus in Eastern Europe and Siberia. The virus is maintained through transstadial transmission as ticks progress from larva to nymph to adult, and by transovarial passage from adult females to their offspring.
Reservoir vertebrates include small mammals such as rodents (e.g., Apodemus field mice, Myodes voles) and, to a lesser extent, birds that transport infected ticks across regions. Infected hosts develop low‑grade viremia sufficient to infect feeding ticks, perpetuating the enzootic cycle without causing overt disease in the reservoir species.
Geographically, endemic zones span temperate forested areas of Eurasia, extending from the Baltic states and Scandinavia through Central Europe to the Russian Far East and parts of China and Japan. Altitudinal limits correspond to tick habitat suitability, typically below 1 500 m where humidity and temperature support tick development.
Human cases arise when infected nymphs or adults attach to skin, usually during outdoor activities in endemic habitats. The virus’s origin in each focus is traced to the local wildlife‑tick interaction, with no single point source but a network of overlapping natural cycles sustained by the described vector‑host relationships.