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Microbiology, pathogenesis, and epidemiology of relapsing fever

Alan G Barbour, MD
Section Editor
Daniel J Sexton, MD
Deputy Editor
Jennifer Mitty, MD, MPH


Relapsing fever, which is caused by spirochetes of the genus Borrelia, is characterized by recurrent episodes of fever that accompany spirochetemia. It is an arthropod-borne infection that occurs in two major forms: tick-borne and louse-borne [1,2].

Tick-borne relapsing fever is a zoonosis (ie, an animal disease that is transmissible to humans). The two main Borrelia spp involved in North America are Borrelia hermsii (in the mountainous West) and Borrelia turicatae (in the Southwest and South Central region), although rare cases of human infection with Borrelia parkeri have also been reported in the United States. Other tick-borne species cause relapsing fever on other continents.

Louse-borne relapsing fever is caused by Borrelia recurrentis. It is principally a disease seen in the developing world. It is spread from person to person by the body louse and can result in large epidemics.

The microbiology, pathogenesis, and epidemiology of relapsing fever will be reviewed here. The clinical manifestations, diagnosis, treatment, and prevention of this disorder, as well as a related spirochete, Borrelia miyamotoi, are discussed separately. (See "Borrelia miyamotoi infection" and "Clinical features, diagnosis, and management of relapsing fever".)


Taxonomy — The agents of relapsing fever are spirochetes, a morphologically unique group of bacteria that differ substantially from both gram-negative and gram-positive organisms [3]. Spirochetes can cause a diverse group of diseases, including syphilis, leptospirosis, Lyme disease, and B. miyamotoi infection. (See "Syphilis: Epidemiology, pathophysiology, and clinical manifestations in HIV-uninfected patients" and "Epidemiology, microbiology, clinical manifestations, and diagnosis of leptospirosis" and "Epidemiology of Lyme disease".)

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Literature review current through: Oct 2017. | This topic last updated: Nov 11, 2017.
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