Relapsing Fever

Relapsing fever is an arthropod-borne infection that occurs in two forms: tick-borne relapsing fever (TBRF) and louse-borne relapsing fever (LBRF). The etiologic agents of relapsing fever are several species of spirochetes in the genus Borrelia. TBRF is usually a zoonosis and is endemic on most continents, each with a characteristic Borrelia species. Examples are Borrelia hermsii in North America and Borrelia duttonii in Africa. LBRF is caused by a single species, Borrelia recurrentis. The multiple episodes of fever and disease relapses in both TBRF and LBRF are due to antigenic variation by the spirochetes. But elucidation of the pathogenesis and genetics of relapsing fever agents awaited the developments in the field of molecular biology. This chapter first talks about biology, genetics, phylogenetic classification, life cycle and ecology of relapsing fever Borrelia species. Antigenic variation by relapsing fever Borrelia spp. is among the most extensive of any vector-borne bacterial or protozoal parasite. Its characteristics most closely resemble the antigenic variation manifested by African trypanosomes. The chapter ends with a discussion on epidemiology, clinical manifestations, diagnosis, treatment, and prevention of relapsing fever.