From whom do ticks acquire encephalitis? - briefly
Ticks become carriers of encephalitis viruses by feeding on infected vertebrate hosts, chiefly small mammals such as rodents and, in some regions, birds. These animals serve as the natural reservoirs that transmit the virus to the tick during blood meals.
From whom do ticks acquire encephalitis? - in detail
Ticks become infected with the tick‑borne encephalitis virus (TBEV) primarily by feeding on vertebrate reservoirs that sustain the virus in nature. The virus circulates among small mammals, certain bird species, and occasionally larger ungulates, which together maintain the enzootic cycle.
The main reservoir hosts are:
- Rodents – bank voles (Myodes glareolus), yellow‑necked mice (Apodemus flavicollis), and other field mice. Their high population density and frequent exposure to questing larvae make them the principal source of infection for immature ticks.
- Ground‑dwelling birds – common blackbird (Turdus merula), European robin (Erithacus rubecula), and other passerines. Birds transport infected ticks across habitats and provide blood meals for larvae and nymphs.
- Lagomorphs – European hare (Lepus europaeus) and wild rabbits (Oryctolagus cuniculus) can harbor the virus and contribute to tick infection, especially in areas where rodent numbers fluctuate.
- Ungulates – roe deer (Capreolus capreolus), red deer (Cervus elaphus), and other cervids. While they are not efficient virus reservoirs, they support large adult tick populations and enable co‑feeding transmission, whereby infected and uninfected ticks feed simultaneously on the same host without systemic infection.
Transmission occurs through several mechanisms:
- Acquisition during blood meal – A larval tick that feeds on an infected rodent or bird ingests the virus, which persists through molting (trans‑stadial transmission) to the nymphal stage.
- Co‑feeding – Infected and uninfected ticks attached to the same host area exchange virus locally in the skin, allowing infection of ticks even when the host shows no viremia.
- Vertical transmission – Rarely, infected females can pass the virus to their offspring (trans‑ovarial transmission), contributing to low‑level maintenance of the virus in tick populations.
Humans are incidental hosts; they acquire the virus from infected nymphs or adults, not the other way around. The enzootic cycle therefore relies on the interaction of ticks with the wildlife species listed above, which collectively supply the virus needed for tick infection and subsequent human disease risk.