Where do ticks become infected? - briefly
Ticks acquire pathogens during blood meals from infected vertebrate hosts, including mammals, birds, and reptiles. The infection can persist through molting, enabling the tick to transmit the agent to later hosts.
Where do ticks become infected? - in detail
Ticks acquire infectious agents primarily during blood meals from vertebrate hosts that serve as reservoirs. Larval and nymphal stages feed on small mammals, birds, and reptiles; adults commonly infest larger mammals such as deer, livestock, and humans. When a tick attaches to an infected host, pathogens enter the tick’s midgut and may migrate to salivary glands, preparing the vector for transmission in subsequent feedings.
Key mechanisms of acquisition include:
- Horizontal transmission: Direct uptake of microbes from the host’s bloodstream during feeding.
- Co‑feeding transmission: Transfer of pathogens between adjacent ticks feeding simultaneously on the same host, even if the host’s systemic infection is absent.
- Transstadial maintenance: Persistence of the pathogen through the tick’s developmental stages (larva → nymph → adult), ensuring continued infectivity.
- Transovarial passage: Vertical transfer of certain agents, such as Rickettsia spp., from adult females to their eggs, leading to infected larvae without a prior blood meal.
Reservoir competence varies among species. For Lyme‑disease spirochetes (Borrelia burgdorferi), white‑footed mice (Peromyscus leucopus) and certain bird species constitute primary sources. Anaplasma phagocytophilum is frequently acquired from small mammals and ruminants, while Babesia microti is predominantly sourced from rodents. Tick‑borne viruses, such as Powassan, often originate from small mammals and ground‑dwelling birds.
Environmental factors influence infection risk. Dense vegetation, leaf litter, and humid microclimates support higher tick densities and increase contact with reservoir hosts. Seasonal activity patterns dictate which life stage is prevalent, shaping the probability of pathogen acquisition at specific times of the year.
In summary, ticks become infected through feeding on competent reservoir hosts, by co‑feeding on shared hosts, and, for some agents, via vertical transmission. The combination of host species, life‑stage feeding behavior, and ecological conditions determines the spatial and temporal distribution of infected vectors.