Tick-borne relapsing fever

Abstract

Each year, many residents of and visitors to endemic regions of the western United States are exposed to the tick vectors of tick-borne relapsing fever (TBRF), Ornithodoros hermsi, Ornithodoros turicata, or Ornithodoros parkeri. This disease is remarkable because the human host is unaware of the tick bite, usually becomes very ill, may experience an exacerbation of symptoms rather than improvement shortly after beginning appropriate treatment, and, despite often high numbers of the etiologic organism in the blood, rarely dies as a result of the illness. Although relapsing fever is acquired in many parts of the world, this article focuses primarily on knowledge about TBRF in North America.

Fig. 1

Reported cases of tick-borne relapsing fever by county, United States, 1990 to 2002 (From Centers for Disease Control and Prevention. Tick borne relapsing fever trends. Available at: http://www.cdc.gov/ncidod/dvbid/RelapsingFever/TBRF_DiseaseTrends.html. Accessed December 12, 2007.)

Fig. 2

Ornithodoros hermsi (right) and Ornithodoros turicata (left).

Fig. 3

Borrelia hermsii in a stained peripheral blood smear from an infected woman. (From Badger M. Tick talk: Unusually severe case of tick-borne relapsing fever: Case report and review of the literature. Wilderness Env Med J 2008, in press; with permission.)