What is a tick infected with? - briefly
Ticks commonly carry pathogens such as the bacterium Borrelia burgdorferi (Lyme disease), other bacteria (Anaplasma, Rickettsia), the protozoan Babesia, and viruses (Powassan, tick‑borne encephalitis).
What is a tick infected with? - in detail
Ticks are vectors for a broad spectrum of pathogenic microorganisms, including bacteria, viruses, and protozoa. The composition of the infectious load varies with tick species, developmental stage, and geographic region.
Bacterial agents transmitted by hard ticks encompass several medically significant species. Borrelia burgdorferi complex organisms cause Lyme disease and are most often associated with Ixodes spp. Anaplasma phagocytophilum induces human granulocytic anaplasmosis, also vectored by Ixodes ticks. Ehrlichia chaffeensis and Ehrlichia ewingii produce ehrlichiosis and are linked to the lone‑star tick (Amblyomma americanum). Rickettsial pathogens such as Rickettsia rickettsii (Rocky Mountain spotted fever) and Rickettsia parkeri are transmitted by Dermacentor and Amblyomma species, respectively. Bartonella henselae has been identified in several tick genera, though its role in human disease remains under investigation.
Viral infections acquired through tick bites include flaviviruses and other RNA viruses. Tick‑borne encephalitis virus (TBEV) circulates in Ixodes ricinus and I. persulcatus across Europe and Asia, causing encephalitis. Powassan virus, a flavivirus carried by Ixodes ticks in North America, leads to severe neuroinvasive disease. Crimean‑Congo hemorrhagic fever virus, transmitted by Hyalomma spp., produces hemorrhagic fever in Africa, Asia, and parts of Europe. Emerging agents such as Heartland virus and Bourbon virus have been isolated from Amblyomma americanum and Amblyomma cajennense in the United States, respectively.
Protozoan parasites also rely on ticks for transmission. Babesia microti, the causative agent of babesiosis, is primarily spread by Ixodes scapularis in the northeastern United States. Other Babesia species (B. divergens, B. duncani) are linked to Ixodes and Dermacentor ticks in Europe and the western United States. Hepatozoon spp., though rare in humans, have been detected in Rhipicephalus and Amblyomma ticks and can affect animals.
Co‑infection is common when a single tick carries multiple pathogens. Simultaneous transmission of B. burgdorferi and A. phagocytophilum or of B. burgdorferi and B. microti increases disease severity and complicates diagnosis. Infection rates differ among life stages; nymphs often exhibit higher pathogen prevalence because they feed on a broader host range and are less likely to be removed promptly.
Transmission requires prolonged attachment; most bacteria become viable in the host after 24–48 hours of feeding, whereas viruses may be transmitted within a few hours. Salivary secretions contain immunomodulatory compounds that facilitate pathogen entry.
Geographic distribution dictates pathogen exposure. In North America, Ixodes scapularis dominates the northeastern and upper Midwestern regions, carrying Lyme disease, anaplasmosis, and babesiosis. In the southern United States, Amblyomma americanum is prevalent, transmitting ehrlichiosis, Heartland virus, and Southern tick‑associated rash illness. In Europe and Asia, Ixodes ricinus and I. persulcatus spread Lyme disease, TBEV, and Anaplasma spp. In arid and semi‑arid zones, Hyalomma ticks transmit Crimean‑Congo hemorrhagic fever virus and Rickettsia spp.
Understanding the diversity of tick‑borne pathogens, their vectors, and regional patterns is essential for accurate diagnosis, effective treatment, and targeted prevention strategies.