How is encephalitis transmitted by a tick? - briefly
Ticks spread encephalitis by injecting virus‑laden saliva into the host during a blood meal, allowing the pathogen to enter the circulatory system and reach the central nervous system.
How is encephalitis transmitted by a tick? - in detail
Ticks acquire encephalitic viruses while feeding on infected vertebrate hosts. The virus replicates in the tick’s salivary glands and midgut, establishing a persistent infection that can be transmitted during subsequent blood meals. When a tick attaches to a new host, it inserts its hypostome and secretes saliva that contains anticoagulants, immunomodulatory proteins, and, if present, viral particles. Within minutes to a few hours of attachment, the virus enters the host’s dermal capillaries and spreads via the bloodstream to the central nervous system, where it induces inflammation of the brain and meninges.
Key factors influencing transmission:
- Tick species – Ixodes scapularis, Ixodes ricinus, and Dermacentor spp. are the primary vectors for Powassan virus and tick‑borne encephalitis virus.
- Viral load in the tick – Higher concentrations in salivary glands increase the probability of successful inoculation.
- Feeding duration – Transmission risk rises sharply after 24 hours of attachment; some viruses can be transmitted earlier, within 15–30 minutes.
- Host immune status – Immunocompromised individuals may develop severe encephalitis after a lower inoculum.
The transmission cycle proceeds as follows:
- Acquisition – Larval or nymphal ticks feed on a viremic animal (e.g., small mammals, birds) and ingest the virus.
- Replication – The pathogen replicates in the tick’s internal tissues, migrating to the salivary glands.
- Maintenance – The virus persists through molting, allowing the next developmental stage to remain infectious.
- Inoculation – During a subsequent blood meal, the tick releases viral particles with saliva into the host’s skin.
- Dissemination – The virus travels to the central nervous system, causing encephalitic disease.
Prevention relies on minimizing tick exposure, promptly removing attached ticks, and using repellents containing DEET or permethrin. Early diagnosis and antiviral or supportive therapy improve outcomes, but no specific vaccine exists for most tick‑borne encephalitic viruses in the United States.