How do encephalitic ticks get infected? - briefly
Encephalitic ticks acquire the virus by feeding on infected vertebrate reservoirs, primarily rodents and birds. The pathogen survives molting, keeping the tick infectious through later life stages.
How do encephalitic ticks get infected? - in detail
Ticks become carriers of encephalitic viruses through several biological pathways that operate at the level of the arthropod’s life cycle and its interactions with vertebrate hosts. The primary route is acquisition of virus particles while feeding on an infected animal. When a tick attaches to a mammal or bird that harbors a circulating encephalitis virus, the blood meal introduces virions into the tick’s midgut. The virus then penetrates the gut epithelium, replicates in the hemocoel, and disseminates to the salivary glands, where it becomes available for subsequent transmission.
A second mechanism involves transstadial persistence. After an infected larva molts into a nymph, the virus can survive the metamorphic process and remain infectious in the new stage. This continuity enables the tick to transmit the pathogen during later feedings without requiring a new infection source.
Certain tick species also support transovarial passage. Infected females transmit virions to their offspring through the ovaries, resulting in infected larvae that emerge already capable of virus transmission. This vertical route sustains pathogen presence within tick populations even when vertebrate reservoir density is low.
Co‑feeding transmission provides an additional, non‑systemic pathway. When multiple ticks feed in close proximity on the same host, virus particles can move directly from the saliva of an infected tick to neighboring uninfected ticks through the host’s skin and interstitial fluid, bypassing the need for systemic host infection.
Reservoir competence of specific vertebrates influences the infection pressure on ticks. Small mammals such as rodents and certain birds maintain high viremia levels for the duration required to infect feeding ticks. The prevalence of these reservoirs, their population dynamics, and their habitat overlap with tick activity zones determine the likelihood of virus acquisition.
Environmental factors modulate each of these processes. Temperature affects viral replication rates within the tick; warmer conditions accelerate replication, shortening the extrinsic incubation period. Humidity influences tick survival and questing behavior, indirectly shaping contact rates with hosts. Seasonal patterns dictate the timing of life‑stage transitions, aligning periods of peak host availability with the developmental stages most susceptible to infection.
In summary, ticks acquire encephalitic viruses primarily through ingestion of infected blood, retain the pathogen across developmental stages, may inherit it from infected mothers, and can acquire it via co‑feeding. These mechanisms operate within a complex ecological framework defined by reservoir host competence, environmental conditions, and tick phenology.