From whom do ticks become infected? - briefly
Ticks acquire pathogens during blood meals from infected vertebrate hosts, primarily small mammals such as rodents, as well as deer, birds, and occasionally humans. The organism is transmitted through the tick’s saliva while it is attached.
From whom do ticks become infected? - in detail
Ticks acquire infectious agents almost exclusively while feeding on vertebrate hosts that already harbor the pathogen. During a blood meal, the tick’s salivary secretions allow the pathogen to move from the host’s bloodstream into the tick’s midgut, where it can survive, multiply, and later be transmitted to the next host.
Typical reservoir hosts for common tick‑borne agents
- Small mammals (white‑footed mouse, voles, shrews) – primary sources of Borrelia burgdorferi (Lyme disease), Anaplasma phagocytophilum, and Babesia microti.
- Birds (songbirds, ground‑feeding species) – carriers of Borrelia genospecies, Rickettsia spp., and certain Anaplasma strains; can transport infected ticks over long distances.
- Reptiles and amphibians (lizards, salamanders) – reservoirs for Borrelia species that infect Ixodes pacificus in the western United States.
- Large mammals (white‑tailed deer, elk, moose) – provide blood meals for nymphs and adults; deer amplify Borrelia and Anaplasma but are not competent reservoirs for the spirochete itself, while they sustain Babesia and Rickettsia infections.
- Domestic animals (dogs, cattle, horses) – source of Rickettsia rickettsii (Rocky Mountain spotted fever), Coxiella burnetii, and Ehrlichia spp. in certain regions.
Stage‑specific acquisition
- Larvae: hatch uninfected; acquire pathogens from first host, usually a small mammal or bird.
- Nymphs: retain infections obtained as larvae (trans‑stadial transmission) and can acquire additional agents from second hosts, often the same small‑mammal community.
- Adults: feed on larger mammals; transmit pathogens acquired earlier and may acquire new ones from the adult host.
Additional transmission routes
- Co‑feeding: adjacent ticks feeding simultaneously on the same host can exchange pathogens without systemic infection of the host.
- Transovarial transmission: some agents (e.g., Rickettsia rickettsii, Coxiella burnetii) pass from infected female ticks to their eggs, producing infected offspring without a vertebrate reservoir.
In summary, ticks become infected through direct ingestion of pathogen‑laden blood from a range of vertebrate reservoirs, with the specific host species and tick life stage determining which agents are most likely to be acquired. Co‑feeding and vertical transmission supplement this primary route, ensuring maintenance of certain pathogens within tick populations even when vertebrate reservoirs are scarce.