Why does a tick become encephalitic? - briefly
Ticks acquire neurotropic flaviviruses, chiefly the «tick‑borne encephalitis virus», from infected vertebrate hosts during blood meals. The virus replicates in the tick’s salivary glands and is introduced into a new host while feeding, provoking inflammation of the central nervous system.
Why does a tick become encephalitic? - in detail
Tick‑borne encephalitis (TBE) results from infection with the Tick‑borne encephalitis virus, a flavivirus transmitted by Ixodes species. The virus circulates among small mammals, primarily rodents, which serve as natural reservoirs. When a larval or nymphal tick feeds on an infected host, the virus enters the tick’s midgut, replicates, and migrates to the salivary glands. Subsequent blood meals allow direct inoculation of viral particles into a new host.
Key determinants that enable a tick to act as a vector for encephalitic disease include:
- Presence of viable virus in the tick’s salivary glands.
- Efficient replication of the virus within the arthropod, maintaining infectivity across developmental stages.
- Salivary proteins that suppress host immune responses, facilitating viral entry.
- Co‑feeding transmission, where uninfected ticks acquire virus from nearby infected ticks without systemic host infection.
- Environmental factors—temperature, humidity, and host density—that increase tick activity and feeding frequency.
After transmission, the virus disseminates from the skin to regional lymph nodes, enters the bloodstream, and crosses the blood‑brain barrier. In the central nervous system, viral replication triggers inflammation, neuronal loss, and the clinical manifestations of encephalitis.
Control measures focus on reducing tick exposure and preventing infection:
- Vaccination against the virus for populations in endemic regions.
- Personal protective practices: long clothing, repellents containing DEET or permethrin, and regular tick checks.
- Habitat management to lower rodent populations and limit tick habitats.
Understanding the biological cycle of the virus and the physiological adaptations of the tick clarifies why the arthropod can serve as an encephalitic vector.