Brief Summary

Ornithodoros species are soft ticks (Family Argasidae). Included in this genus are several vectors of tick-borne relapsing fever (TBRF) in humans, including O. hermsi, which is found in the United States and can transmit the spirochaete bacteria responsible for TBRF.

Ornithodoros hermsi Wheeler (Acari: Argasidae) is the vector of the spirochaete bacterium Borrelia hermsii, the primary cause of TBRF in North America (McCoy et al. 2010). TBRF is endemic to high elevation coniferous forests of the western United States and southern British Columbia, Canada. Patients usually become ill after they have slept in cabins infested with spirochete-infected ticks that feed quickly during the night. The illness has an incubation period ranging from 4 to more than 18 days and is characterized by recurring episodes of fever accompanied by a variety of other manifestations, including headache, myalgia (muscle pain), arthralgia (joint pain), chills, vomiting, and abdominal pain. Relapsing fever is confirmed by the microscopic detection of spirochetes in the patient’s blood. (Dworkin et al. 2002; Schwan et al. 2003 and references therein)

Like other argasids, Ornithodoros ticks have multihost life cycles. Argasid ticks have two or more nymphal stages, each requiring a blood meal from a host. Unlike the ixodid (hard) ticks, which stay attached to their hosts for up to several days while feeding, most argasid ticks are adapted to feeding rapidly (for about an hour), then dropping off the host. (Centers for Disease Control Parasites and Health website)

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Ornithodoros hermsi

Ornithodoros hermsi is a species of soft tick. It can be infected with Borrelia hermsii.[1]


Ornithodoros hermsi is a soft-bodied tick of the family Argasidae. It is one of the smallest ticks of the species Ornithodoros.[2] Females are larger than the males.[3] O. hermsi has a multihost lifecycle,[1] and some females have been observed to live four years without any blood meals.[3] They are parasites of rodents and other small mammals. The most favored host is the western chipmunk, Eutamias spp.[3]


As do all other species of ticks, O. hermsi begin as eggs, then larvae, then nymphs, to adult ticks.[4] O. hermsi has two larval molts and three nymphal stages.[5] The nymphal blood meals and the greater volume of blood intake will increase the development from nymphs to adults and decrease the number of nymphal stages.[1]


O. hermsi is found in the northwestern region of the United States, including Washington, Oregon, California, Idaho, Colorado, and even northern Arizona and New Mexico. Additionally, the species is found in southwest British Columbia, Canada.[6]

The ticks are found in timbered regions and at high altitudes. Wood used for fuel and lumber are common locations, as are hollow pine logs, Douglas firs, and wooden cabins.[7] O. hermsi has been found in the nests of birds and rodents.[3]

Medical and veterinary importance[edit]

This species is a vector of Borrelia hermsii, which can cause tick-borne relapsing fever in humans.[2] which are spread from O. hermsi to animals to humans or directly to humans.[8] Unlike hard-bodied ticks, Ixodidae, O. hermsi feeds on a host for a short period ranging from 15–20 minutes.[9] They often feed at night.[1] The bites are not painful nor noticeable, which is dangerous as victims of the bite will not know they are affected until symptoms of TBRF appear.[3] The a higher transmission of B. hermsii in late-stage nymphs and adult ticks is because they have larger blood meals and, therefore, longer feeding times.[10]


  1. ^ a b c d Schwan TG, Raffel SJ, Schrumpf ME, et al. (July 2009). "Tick-borne relapsing fever and Borrelia hermsii, Los Angeles County, California, USA". Emerging Infect. Dis. 15 (7): 1026–31. doi:10.3201/eid1507.090223. PMC 2744237. PMID 19624916. 
  2. ^ a b McCoy, Brandi N.; Sandra J. Raffel, Job E. Lopez and Tom G. Schwan (25 August 2010). "Bloodmeal Size and Spirochete Acquisition of Ornithodoros hermsi (Acari: Argasidae) During Feeding". Journal of Medical Entomology 47 (6): 1164–1172. doi:10.1603/ME10175. Retrieved 11/4/2013.  Check date values in: |accessdate= (help)
  3. ^ a b c d e Wheeler, Charles M. (February 1943). "A Contribution to the Biology of Ornithodoros hermsi Wheeler, Herms and Meyer". The Journal of Parasitology 29 (1): 33–41. JSTOR 3272745. 
  4. ^ Bay, D.E.; R.L. Harris (1988). Introduction to Veterinary Entomology (A Guide to Livestock Insects). Robert Harris Publisher. p. 72. ISBN 0-9624083-0-1. 
  5. ^ Shapiro, Leo. "Brief Summary". Encyclopedia of Life. Retrieved 5 November 2013. 
  6. ^ Schwan, Tom G; Paul F. Policastro; Zachary Miller; Robert L. Thompson; Todd Damrow; James E. Keirans (September 2003). "Tick-borne Relapsing Fever Caused by Borrelia hermsii, Montana". Emerging Infectious Diseases 9 (9): 1151–1154. doi:10.3201/eid0909.030280. PMC 3016790. PMID 14519254. Retrieved 5 November 2013. 
  7. ^ Davis, Gordon E. (10 October 1941). "Ornithodoros hermsi and Relapsing Fever in Oregon". Public Health Reports (1896-1970) 56 (41): 2010–2012. JSTOR 4583889. 
  8. ^ "Relapsing Fever" (Web). Encyclopaedia Britannica Online Academic Edition. Encyclopaedia Britannica Inc. 2013. Retrieved 5 November 2013. 
  9. ^ Bay, D.E.; R.L. Harris (1988). Introduction to Veterinary Entomology (A Guide to Livestock Insects). Robert Harris Publisher. p. 73. ISBN 0-9624083-0-1. 
  10. ^ Lopez, Job E.; Brandi N. McCoy, Benjamin J. Krajacich and Tom G. Schwan (July 2011). "Acquisition and Subsequent Transmission of Borrelia hermsii by the Soft Tick Ornithodoros hermsi". Journal of Medical Entomology 48 (4): 891–895. doi:10.1603/ME10283. Retrieved 5 November 2013. 
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