How does a tick acquire encephalitis? - briefly
Ticks become infected with encephalitis viruses when they ingest blood from vertebrate hosts that are already carrying the pathogen, most often small mammals or birds. The virus then multiplies in the tick’s salivary glands, enabling it to be passed to the next animal the tick bites.
How does a tick acquire encephalitis? - in detail
Ticks become infected with encephalitis viruses primarily through blood meals taken from vertebrate reservoir hosts that carry the pathogen. The virus circulates in small mammals such as rodents, as well as in birds and larger mammals, which maintain high viremia levels sufficient for transmission. When a larval or nymphal tick attaches to an infected host, the virus enters the tick’s midgut and then spreads to salivary glands, enabling subsequent transmission to new hosts during later feedings.
The infection persists across developmental stages—a process known as transstadial transmission. After the larva molts into a nymph, the virus remains viable, allowing the tick to infect additional hosts without reacquisition. Vertical transmission (from adult female to offspring) occurs at a low frequency, contributing minimally to the overall prevalence of the pathogen in tick populations.
Key factors influencing acquisition include:
- Host competence: Species that develop high viral loads in the bloodstream provide efficient sources of infection.
- Tick feeding duration: Longer attachment periods increase the likelihood of virus uptake.
- Environmental conditions: Temperature and humidity affect tick activity and host‑tick contact rates, indirectly shaping infection opportunities.
- Geographic distribution of reservoirs: Areas with dense populations of competent hosts exhibit higher prevalence of infected ticks.
After infection, the virus replicates within the tick’s tissues, particularly the salivary glands, which are the primary site for virus release during subsequent blood meals. This biological cycle sustains the enzootic focus of tick‑borne encephalitis and underlies the risk of human exposure in endemic regions.