Where do ticks acquire encephalitis and borreliosis? - briefly
Ticks become infected with the viruses and bacteria that cause encephalitis and Lyme disease while feeding on reservoir hosts such as rodents, birds, and deer in endemic regions. These pathogens are transmitted to the tick during the blood meal and persist through subsequent life stages.
Where do ticks acquire encephalitis and borreliosis? - in detail
Ticks become vectors for the agents of tick‑borne encephalitis (TBE) and Lyme disease during their blood meals from infected vertebrate hosts. The acquisition sites correspond to habitats where these reservoir species are abundant and where tick development stages can survive.
The primary environments supporting pathogen transmission include:
- Deciduous and mixed forests with leaf litter that retains moisture, providing optimal microclimate for Ixodes ricinus and Ixodes persulcatus larvae and nymphs.
- Shrub‑covered meadow edges and clearings where rodents and ground‑dwelling birds are frequent.
- Alpine and sub‑alpine zones with dense understory, especially in Central and Eastern Europe and Siberia, where the tick‑borne encephalitis virus is endemic.
- Urban parks and peri‑urban green spaces that host small mammals such as the bank vole (Myodes glareolus) and the wood mouse (Apodemus sylvaticus).
Reservoir hosts differ slightly between the two pathogens:
- TBE virus is maintained chiefly in small mammals (e.g., rodents) and certain bird species that circulate the virus without severe disease.
- Borrelia burgdorferi sensu lato complex relies on a broader range of mammals, including rodents, shrews, and larger mammals such as deer, which facilitate tick feeding but are not competent reservoirs for the spirochete.
Transmission dynamics follow a predictable pattern: larvae hatch uninfected, feed on a host that may carry either pathogen, and become infected. Infected nymphs, which are most often responsible for human bites, acquire the agents from the same ecological niches during their second blood meal. Adult ticks can also become infected while feeding on competent hosts, sustaining the cycle in the same habitats.
Geographically, the risk zones align with the distribution of the tick species and their reservoirs:
- Europe: Central, Northern, and Eastern regions, especially the Baltic states, Scandinavia, and the Czech Republic.
- Asia: Siberia, Japan, and parts of China where I. persulcatus predominates.
- North America: Eastern United States and southeastern Canada, where I. scapularis and I. pacificus transmit Lyme spirochetes; TBE is absent, but related encephalitis viruses occur in limited western areas.
In summary, ticks acquire encephalitis‑causing viruses and Lyme‑causing spirochetes in moist, vegetated environments that support dense populations of small mammal and bird reservoirs. The process occurs during larval and nymphal feeding stages, with nymphs representing the principal vector stage for human exposure.