How is encephalitis transmitted from tick to tick? - briefly
Encephalitis viruses are not transferred directly from one tick to another; a tick becomes infected by feeding on a vertebrate host that carries the pathogen. The infected tick then introduces the virus into a new host during subsequent blood meals.
How is encephalitis transmitted from tick to tick? - in detail
Encephalitis agents that circulate in tick populations are passed from one arthropod to another primarily through co‑feeding and vertical transmission.
During co‑feeding, an infected tick and an uninfected tick attach to the same host simultaneously or in close succession. Saliva from the infected individual introduces the virus into the host’s skin, where it remains localized without triggering a systemic infection. The neighboring uninfected tick, feeding on the same microenvironment, ingests the pathogen directly from the host’s dermal tissue or from the infected tick’s saliva that has diffused into the feeding site. This route bypasses the need for the host to develop a detectable viremia, allowing efficient spread among ticks that share a host.
Vertical transmission occurs when an adult female tick harbors the virus in her ovaries. The pathogen is incorporated into developing oocytes, resulting in infected larvae that emerge already carrying the agent. This mechanism sustains the pathogen within tick colonies across generations, even when external acquisition is limited.
Both pathways are reinforced by specific biological factors:
- Salivary gland infection enhances viral release during feeding.
- Tick immune modulation reduces clearance of the pathogen.
- Host skin microcirculation provides a stable niche for virus persistence during co‑feeding.
Together, co‑feeding and transovarial passage constitute the principal means by which encephalitis‑causing viruses propagate from one tick to another, ensuring continual circulation in vector populations.