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Relapsing fever is an acute relapsing systemic illness caused by infection with spirochetal bacteria in the genus Borrelia. Louse-borne (epidemic) relapsing fever (LBRF) is caused by Borrelia recurrentis, and tick-borne (endemic) relapsing fever (TBRF) by several closely related species of Borrelia. Louse-borne relapsing fever is transmitted by the human body louse, Pediculus humanus; TBRF is transmitted by the bite of various soft-bodied ticks of the genus Ornithodorus. LBRF has, for the past several decades, been reported only in Ethiopia and several surrounding countries. It especially affects populations that are crowded, impoverished, and displaced by war or famine—all factors associated with poor hygiene and lice infestation. TBRF occurs in scattered temperate and tropical areas worldwide; in the United States it occurs almost exclusively in the western states, especially in forested, mountainous areas. TBRF typically occurs in small, often familial, clusters, and it is associated with sleeping in rodent- and tick-infested homes or cabins.

Following a usual incubation period of four to seven days, illness begins with the abrupt onset of fever, aches and pains in muscles and joints, headache, shaking chills, sweats, loss of appetite, weakness, and prostration. Periods of fever usually last for several days, typically ending with a crisis characterized by rigors and rising temperature, followed by an abrupt fall in temperature, profuse sweating, and hypotension. Untreated, relapses may recur after intervals of several days to a week or more. An average of three, and as many as ten, relapses may occur in TBRF, while only one to three relapses occur in LBRF. Relapses are associated with antigenic changes in bacterial outer-surface proteins.

The diagnosis of borrelial fevers is made by eliciting a history of possible infective exposure, by the typical relapsing character of the illness, and by identifying borreliae in the patient's blood. Relapsing fever is readily cured with any of several antibiotics—tetracyclines, erythromycin, and chloramphenicol are recommended choices. Control and prevention of LBRF relies on basic sanitation and hygiene to prevent or rid clothing and bedclothes of body lice, early case detection, and treatment. TBRF is prevented by removing rodent nests from buildings, rodent-proofing homes and cabins, and treating suspected tick harborage with chemical acaricides.

DAVID T. DENNIS

(SEE ALSO: Communicable Disease Control; Environmental Determinants of Health; Vector-Borne Diseases)