Ornithodoros hermsi is a soft bodied tick, which is part of the family Argasidae. It is one of the smallest ticks of the species Ornithodoros. Females are larger than the males. O. hermsi has a multihost life-cycle  and some females have been observed to last four years without any blood meals. They are a parasite of rodents and other small mammals. The most favored host is the western chipmunk, Eutanmias spp.
As do all other species of ticks, O. hermsi begin as eggs, then larvae, then nymphs, to adult ticks. O. hermsi has two larval molts and has 3 nymphal stages. 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.
Ornithodoros hermsi is found in the northwestern region of the United States, in states including Washington, Oregon, California, Idaho, Colorado, and even northern Arizona and New Mexico. Additionally, the species is found in southwest British Columbia, Canada.
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. O. hermsi have been found in the nests of birds and rodents.
Medical and Veterinary Importance
Ornithodros hermsi is a vector of Borrelia hermsii which can cause tick-borne relapsing fever in humans. Tick-borne relapsing fever, TBRF, is spread by the spirochete bacteria in Borrelia hermsii which are spread from O. hermsi to animals to humans or directly to humans. Unlike, hard-bodied ticks, Ixodidae, O. hermsi feeds on a host for a short period ranging from 15–20 minutes. They often feed at night. 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. There is a higher transmission of Borrelia hermsii in late-stage nymphs and adult ticks because they have larger blood meals and, therefore, longer feeding times.
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