Relapsing Fever Ticks-Soft Ticks

These three “soft ticks” are known for causing Tick Borne Relapsing Fever (TBRF) in humans in the US, with Ornithodoros hermsii being the primary vector. Special care should be taken when sleeping or working in or near rodent infested buildings (cabins, hunting camps, barns or outbuildings) where these ticks may reside in nests or burrows.

Ornithodoros hermsi–unfed and fed, CDC credit

Ornithodoros hermsi

This soft tick species is probably the primary vector of one of the agents of tick borne relapsing fever (TBRF), Borrelia hermsii, in humans. It occurs 14 of the western US States. Colorado has been in the top five for reported cases in the western US. Transmission to humans occurs primarily when people sleep in rustic rodent infested vacation or hunting cabins. These ticks most often feed on humans at night for brief periods and then retreat to the host nest. Humans may also encounter these ticks incidentally while spending time near rodent nests or burrows that may have been vacated by the host species including barns, wood piles, and fallen logs. Hosts include sciurids (squirrels, chipmunks, etc.), rats and mice. It is an incidental human biter.

Praire Dog, primary host of O. parkeri

Ornithodoros parkeri

This soft tick species was identified in Moffat County, Colorado and transmits Borrelia parkeri, one of the agents of tick-borne relapsing fever (TBRF). Has been implicated as a potential human health risk in Colorado. Humans may encounter these ticks incidentally while spending time near rodent nests or burrows that may have been vacated by the host species. Hosts are primarily prairie dogs, but also marmots, deer mice, ground squirrels, lagomorphs, weasels, burrowing owls. It is an incidental human biter.

Ornithodoros turicata

This tick “species” seems to include several closely related species, some of which have not been described; it has been implicated as a vector of an agent of tick borne relapsing fever (TBRF), Borrelia parkeri. Hosts include a wide variety of burrowing reptiles, birds, mammals. Infection with this tick commonly occurs after humans explore caves or crawl under buildings, and cases have been described in persons who have handled dead rodents. It is an incidental human biter.