How do ticks become infected with encephalitis? - briefly
Ticks acquire encephalitis viruses by feeding on infected small mammals or birds, allowing the pathogen to persist through the tick’s developmental stages (transstadial transmission). The virus can also spread to other ticks co‑feeding on the same host without the need for systemic infection.
How do ticks become infected with encephalitis? - in detail
Ticks acquire encephalitis‑causing viruses primarily through feeding on infected vertebrate hosts. When a larva, nymph, or adult attaches to a mammal or bird that is viremic, the virus enters the tick’s gut with the ingested blood. The pathogen then traverses the midgut epithelium, disseminates through the hemocoel, and reaches the salivary glands, where it can be transmitted to the next host during subsequent feeding.
Key mechanisms that sustain infection within tick populations include:
- Transstadial transmission – the virus persists as the tick molts from larva to nymph and from nymph to adult, allowing the same individual to carry the pathogen across life stages.
- Transovarial transmission – infected females can pass the virus to their offspring via eggs, establishing infected cohorts without requiring an initial blood meal.
- Co‑feeding transmission – simultaneous feeding by infected and uninfected ticks on the same host enables viral exchange without systemic host viremia, especially when the host’s immune response limits circulating virus.
Reservoir hosts such as small mammals (e.g., rodents) and certain birds maintain high levels of viremia, creating a continuous source of infection for feeding ticks. Environmental conditions that favor tick activity—moderate temperature, high humidity, and adequate vegetation—enhance host‑tick encounters and thus the probability of viral acquisition.
After colonization of the salivary glands, the virus is expelled with saliva during the next blood meal. The recipient host may develop encephalitic disease if the virus reaches the central nervous system, completing the enzootic cycle. Control strategies focus on reducing reservoir host density, limiting tick exposure, and interrupting the transmission pathways described above.