Where does the encephalitis virus come from in ticks? - briefly
Ticks acquire encephalitis‑causing viruses by feeding on infected vertebrate hosts such as rodents, birds, and small mammals; the virus then persists in the tick’s salivary glands, enabling transmission to subsequent hosts.
Where does the encephalitis virus come from in ticks? - in detail
The virus responsible for tick‑borne encephalitis (TBEV) is a flavivirus that circulates primarily between small mammals and hard‑tick vectors. Adult and nymphal stages of Ixodes ricinus in Europe and Ixodes persulcatus in Asia acquire the pathogen while feeding on rodents such as bank voles, wood mice, and shrews that serve as natural reservoirs. These mammals develop transient viremia sufficient to infect feeding ticks but rarely exhibit severe disease.
After ingestion, the virus replicates in the tick midgut epithelium, spreads to the hemocoel, and colonizes the salivary glands. This process enables the tick to transmit infectious particles during subsequent blood meals. The pathogen persists through the tick’s developmental stages (larva → nymph → adult) via transstadial transmission, ensuring continuity of the infection cycle without the need for a new vertebrate host at each molt.
Additional mechanisms sustain viral presence in tick populations:
- Co‑feeding transmission: Adjacent, non‑systemically infected ticks feed simultaneously on the same host, allowing virus exchange without detectable host viremia.
- Transovarial transmission: Infected females can pass the virus to their offspring, though this route contributes modestly to overall prevalence.
- Horizontal spillover: Migratory birds transport infected ticks across regions, expanding the geographic range of the virus.
Environmental factors influence vector competence. Temperature and humidity affect tick activity periods, while habitat characteristics determine host density. Areas with abundant forest understory and leaf litter support higher tick densities and consequently greater virus circulation.
In summary, the encephalitis virus originates from a sylvatic cycle involving rodents as primary reservoirs and hard ticks as vectors. Acquisition occurs during blood feeding, followed by replication, transstadial persistence, and occasional vertical and co‑feeding transmission, all of which maintain the pathogen within tick populations and facilitate human exposure.