Who infected ticks? - briefly
Ticks become carriers of pathogens after feeding on infected animals such as rodents, birds, deer, and other mammals, and some infections are passed directly from an infected female tick to her offspring.
Who infected ticks? - in detail
Ticks acquire infectious agents primarily during blood feeding. The source of infection is the vertebrate host whose blood contains the pathogen. Reservoir species maintain the pathogen in nature and transmit it to feeding ticks. Key reservoirs include small mammals (e.g., white‑footed mice, voles), deer, birds, and reptiles. Each tick species preferentially feeds on a subset of these hosts, shaping the pathogen community it carries.
Pathogens commonly found in ticks are:
- Borrelia burgdorferi sensu lato – bacterial spirochete responsible for Lyme disease; maintained in rodent populations and transmitted to Ixodes species.
- Anaplasma phagocytophilum – intracellular bacterium causing human granulocytic anaplasmosis; circulates among deer and small mammals.
- Rickettsia spp. – includes agents of spotted fever; transmitted by Dermacentor and Amblyomma ticks; reservoirs vary by species but often involve mammals and birds.
- Babesia microti – protozoan causing babesiosis; rodent reservoirs supply infection to Ixodes scapularis.
- Tick‑borne encephalitis virus (TBEV) – flavivirus maintained in small mammals and birds; transmitted by Ixodes ricinus and I. persulcatus.
- Crimean‑Congo hemorrhagic fever virus (CCHFV) – Nairovirus spread by Hyalomma ticks; vertebrate hosts include livestock and wildlife.
In addition to host‑derived infection, ticks can acquire pathogens through:
- Transovarial transmission – infected females pass the agent to offspring via eggs; documented for several Rickettsia species and CCHFV.
- Co‑feeding transmission – adjacent, unattached ticks exchange pathogens while feeding on the same host, even if the host’s systemic infection is absent.
- Sexual transmission – male and female ticks may exchange pathogens during mating; observed for certain Borrelia and Rickettsia strains.
The combination of host diversity, tick feeding behavior, and vertical or horizontal pathogen passage determines which infectious agents are present in a tick population. Understanding these relationships clarifies the origins of tick‑borne infections and informs surveillance and control strategies.