It is the only thing ever tested.
Samples inside ticks….
Bacterial Infections
1a. Lyme Disease (Lyme Borreliosis)
Pathogen: Borrelia burgdorferi (and related species like B. mayonii, B. afzelii, B. garinii)
Description: The most common tick-borne disease in the Northern Hemisphere, characterized initially by an erythema migrans (bullseye) rash, fever, and fatigue, which can progress to joint, heart, and nervous system complications.
Reference: Steere, A. C., Strle, F., Wormser, G. P., Hu, L. T., Branda, J. A., Hovius, J. W., … & Mead, P. S. (2016). Lyme borreliosis. Nature Reviews Disease Primers, 2(1), 1-19.
1b. Bartonellosis (Bartonella Infection)
Pathogens: Bartonella species (most commonly Bartonella henselae, though others like B. vinsonii and B. microti are studied in this context).
Description: Bartonella is the bacteria responsible for Cat Scratch Disease and Trench Fever, traditionally known to be transmitted by fleas, body lice, and sandflies. However, Bartonella DNA is frequently found in Ixodes ticks (the same ticks that carry Lyme disease), and it is often diagnosed as a co-infection in patients with Lyme disease. While transmission by ticks has been proven in animal models, major public health organizations (like the CDC) state that definitive proof of tick-to-human transmission is still lacking. In patients where it is identified as a co-infection, symptoms can include prolonged fever, fatigue, swollen lymph nodes, bone pain, and neurological symptoms.
Reference: Billeter, S. A., Levy, M. G., Chomel, B. B., & Breitschwerdt, E. B. (2008). Vector transmission of Bartonella species with emphasis on the potential for tick transmission. Medical and Veterinary Entomology, 22(1), 1-15.
2. Rocky Mountain Spotted Fever (RMSF)
Pathogen: Rickettsia rickettsii
Description: A severe and potentially fatal bacterial infection prevalent in the Americas, presenting with sudden fever, headache, and a distinct spotted rash.
Reference: Dantas-Torres, F. (2007). Rocky Mountain spotted fever. The Lancet Infectious Diseases, 7(11), 724-732.
3. Other Spotted Fever Rickettsioses (e.g., Boutonneuse Fever, African Tick Bite Fever)
Pathogens: Rickettsia conorii, Rickettsia africae, Rickettsia parkeri, etc.
Description: A group of globally distributed infections causing fever, headache, muscle aches, and often an eschar (a dark scab at the site of the tick bite).
Reference: Parola, P., Paddock, C. D., Socolovschi, C., Labruna, M. B., Mediannikov, O., Kernif, T., … & Raoult, D. (2013). Update on tick-borne rickettsioses around the world: a geographic approach. Clinical Microbiology Reviews, 26(4), 657-702.
4. Human Granulocytic Anaplasmosis (HGA)
Pathogen: Anaplasma phagocytophilum
Description: Infects white blood cells (neutrophils), causing fever, chills, severe headache, and muscle aches. Often transmitted by the same ticks that carry Lyme disease.
Reference: Bakken, J. S., & Dumler, J. S. (2015). Human granulocytic anaplasmosis. Infectious Disease Clinics, 29(2), 341-355.
5. Human Monocytic Ehrlichiosis (HME)
Pathogens: Ehrlichia chaffeensis, Ehrlichia ewingii, Ehrlichia muris eauclairensis
Description: Similar to anaplasmosis but infects monocytes (another type of white blood cell). Symptoms include fever, muscle aches, and sometimes a rash.
Reference: Ismail, N., & McBride, J. W. (2017). Tick-borne emerging infections: ehrlichiosis and anaplasmosis. Clinics in Laboratory Medicine, 37(2), 317-340.
6. Tick-Borne Relapsing Fever (TBRF)
Pathogens: Borrelia hermsii, Borrelia turicatae, Borrelia duttonii, Borrelia miyamotoi
Description: Characterized by recurring episodes of high fever, headache, and muscle/joint aches. Often transmitted by “soft ticks” in rustic cabins, though B. miyamotoi is transmitted by hard (Ixodes) ticks.
Reference: Dworkin, M. S., Schwan, T. G., Anderson Jr, D. E., & Borchardt, S. M. (2008). Tick-borne relapsing fever. Infectious Disease Clinics, 22(3), 449-468.
7. Tularemia
Pathogen: Francisella tularensis
Description: Can be transmitted via tick bites (as well as handling infected animals). Causes high fever and a skin ulcer at the bite site, along with swollen lymph glands.
Reference: Foley, J. E., & Nieto, N. C. (2010). Tularemia. Veterinary Microbiology, 140(3-4), 332-338.
8. Q Fever
Pathogen: Coxiella burnetii
Description: Primarily transmitted via inhalation of infected animal dust, but ticks are known vectors that maintain the bacteria in animal populations and can occasionally transmit it to humans.
Reference: Maurin, M., & Raoult, D. (1999). Q fever. Clinical Microbiology Reviews, 12(4), 518-553.
Parasitic (Protozoan) Infections
9. Babesiosis
Pathogens: Babesia microti, Babesia divergens, Babesia duncani
Description: A malaria-like illness where microscopic parasites infect and destroy red blood cells, leading to hemolytic anemia, fever, chills, and fatigue.
Reference: Vannier, E., & Krause, P. J. (2012). Human babesiosis. New England Journal of Medicine, 366(25), 2397-2407.
Viral Infections
10. Tick-Borne Encephalitis (TBE)
Pathogen: Tick-borne encephalitis virus (TBEV)
Description: Endemic to parts of Europe and Asia. It attacks the central nervous system, potentially leading to meningitis, encephalitis, and long-term neurological damage.
Reference: Lindquist, L., & Vapalahti, O. (2008). Tick-borne encephalitis. The Lancet, 371(9627), 1861-1871.
11. Powassan Virus Disease
Pathogen: Powassan virus (POWV)
Description: A rare but severe North American virus that can cause encephalitis and meningitis. Notably, it can be transmitted by a tick in as little as 15 minutes of attachment.
Reference: Hermance, M. E., & Thangamani, S. (2017). Powassan virus: an emerging arbovirus of public health concern in North America. Vector-Borne and Zoonotic Diseases, 17(7), 453-462.
12. Crimean-Congo Hemorrhagic Fever (CCHF)
Pathogen: Crimean-Congo hemorrhagic fever virus (CCHFV)
Description: Endemic to Africa, the Balkans, the Middle East, and parts of Asia. It causes severe viral hemorrhagic fever outbreaks with a high case fatality rate.
Reference: Bente, D. A., Forrester, N. L., Watts, D. M., McAuley, A. J., Whitehouse, C. A., & Bray, M. (2013). Crimean-Congo hemorrhagic fever: history, epidemiology, pathogenesis, clinical syndrome and genetic diversity. Antiviral Research, 100(1), 159-189.
13. Colorado Tick Fever
Pathogen: Colorado tick fever virus (CTFV)
Description: Found in the mountainous areas of the western US and Canada. Causes a biphasic (two-phase) fever, chills, headache, and body aches.
Reference: Klasco, R. (2002). Colorado tick fever. Medical Clinics of North America, 86(2), 435-440.
14. Omsk Hemorrhagic Fever
Pathogen: Omsk hemorrhagic fever virus (OHFV)
Description: Found in western Siberia. Causes fever, bleeding, and sometimes neurological symptoms.
Reference: Ruzek, D., Yakimenko, V. V., Bakhvalova, V. N., Tikunov, V. E., Tkachev, S. E., & Karan, L. S. (2010). Omsk haemorrhagic fever. The Lancet, 376(9758), 2104-2113.
15. Kyasanur Forest Disease (KFD)
Pathogen: Kyasanur Forest disease virus (KFDV)
Description: Endemic to southwestern India. Causes fever, headache, bleeding, and occasionally neurological symptoms.
Reference: Pattnaik, P. (2006). Kyasanur forest disease: an epidemiological view in India. Reviews in Medical Virology, 16(3), 151-165.
16. Severe Fever With Thrombocytopenia Syndrome (SFTS)
Pathogen: SFTS virus (Bandavirus)
Description: An emerging infectious disease identified in East Asia (China, Japan, South Korea) causing high fever, low platelet count, and multi-organ failure.
Reference: Yu, X. J., Liang, M. F., Zhang, S. Y., Liu, Y., Li, J. D., Sun, Y. L., … & Walker, D. H. (2011). Fever with thrombocytopenia associated with a novel bunyavirus in China. New England Journal of Medicine, 364(16), 1523-1532.
17. Heartland Virus
Pathogen: Heartland virus (HRTV)
Description: Found in the Midwestern and Southern US. Causes fever, fatigue, decreased appetite, and drops in white blood cells and platelets.
Reference: McMullan, L. K., Folk, S. M., Kelly, A. J., MacNeil, A., Goldsmith, C. S., Metcalfe, M. G., … & Nichol, S. T. (2012). A new phlebovirus associated with severe febrile illness in Missouri. New England Journal of Medicine, 367(9), 834-841.
18. Bourbon Virus
Pathogen: Bourbon virus (BRBV)
Description: A rare thogotovirus discovered in the US causing fever, fatigue, rash, and low blood cell counts.
Reference: Kosoy, O. I., Lambert, A. J., Hawkinson, D. J., Pastula, D. M., Goldsmith, C. S., Hunt, D. C., … & Staples, J. E. (2015). Novel thogotovirus associated with febrile illness and death, United States, 2014. Emerging Infectious Diseases, 21(5), 811.
19. Alkhurma Hemorrhagic Fever
Pathogen: Alkhurma hemorrhagic fever virus (AHFV)
Description: Primarily found in Saudi Arabia; closely related to KFDV. Causes fever, headache, joint pain, and hemorrhagic symptoms.
Reference: Zaki, A. M. (1997). Isolation of a flavivirus related to the tick-borne encephalitis complex from human cases in Saudi Arabia. Transactions of the Royal Society of Tropical Medicine and Hygiene, 91(2), 179-181.
Syndromes Of Unknown Or Debated Etiology
20. Southern Tick-Associated Rash Illness (STARI)
Pathogen: Unknown (previously suspected to be Borrelia lonestari, but studies have not confirmed this).
Description: Transmitted by the Lone Star tick in the southeastern US. It produces a bullseye rash indistinguishable from Lyme disease, along with fatigue and muscle pains, but does not progress to the severe systemic symptoms of Lyme.
Reference: Masters, E. J., Grigery, C. N., & Masters, R. W. (2008). STARI, or Masters disease: Lone Star tick-borne erythema migrans. Infectious Disease Clinics, 22(2), 361-376.
A Note On Alpha-Gal Syndrome
While not an infection, it is crucial to mention Alpha-Gal Syndrome. This is a life-threatening meat allergy triggered by the bite of certain ticks (like the Lone Star tick). The tick transfers a sugar molecule (alpha-gal) into the body, causing the immune system to produce antibodies that react severely when the person later consumes mammalian meat.
Reference: Commins, S. P., & Platts-Mills, T. A. (2013). Tick bites and red meat allergy. Current Opinion in Allergy and Clinical Immunology, 13(4), 354-359.
Disclaimer
This list represents the vast majority of established tick-borne human pathogens. Because zoonotic diseases are continually monitored, isolated regional pathogens (like the Yezo virus in Japan or the Alongshan virus in China/Europe) are constantly being added to the medical literature. Always consult with a healthcare provider or an infectious disease specialist if you suspect a tick-borne illness.