relapsing fever

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Definition

Relapsing fever refers to two similar illnesses, both of which cause high fevers. The fevers resolve, only to recur again within about a week.

Description

Relapsing fever is caused by spiral-shaped bacteria of the genus Borrelia. This bacterium lives in rodents and in insects, specifically ticks and body lice. The form of relapsing fever acquired from ticks is slightly different from that acquired from body lice.

In tick-borne relapsing fever (TBRF), rodents (rats, mice, chipmunks, and squirrels) which carry Borrelia are fed upon by ticks. The ticks then acquire the bacteria, and are able to pass it on to humans. TBRF is most common in sub-Saharan Africa, parts of the Mediterranean, areas in the Middle East, India, China, and the south of Russia. Also, Borrelia causing TBRF exist in the western regions of the United States, particularly in mountainous areas. The disease is said to be endemic to these areas, meaning that the causative agents occur naturally and consistently within these locations.

In louse-borne relapsing fever (LBRF), lice acquire Borrelia from humans who are already infected. These lice can then go on to infect other humans. LBRF is said to be epidemic, as opposed to endemic, meaning that it can occur suddenly in large numbers in specific communities of people. LBRF occurs in places where poverty and overcrowding predispose to human infestation with lice. LBRF has flared during wars, when conditions are crowded and good hygiene is next to impossible. At this time, LBRF is found in areas of east and central Africa, China, and in the Andes Mountains of Peru.

— Rosalyn Carson-DeWitt, MD

Any of several infectious diseases characterized by chills and fever and caused by spirochetes transmitted by lice and ticks. Also called recurrent fever.

An acute infectious disease characterized by recurring fever. It is caused by spirochetes of the genus Borrelia and transmitted by the body louse (Pediculus humanus humanus) and by ticks of the genus Ornithodoros.

Louse-borne relapsing fever, caused by Borrelia recurrentis, is typically epidemic. Epidemics, once widespread on all continents, are rare but still occur in certain parts of South America, Africa, and Asia. Tick-borne relapsing fevers are endemic. They are more widely distributed throughout the Eastern and Western hemispheres. At least 15 species of Borrelia have been recognized as causative agents.

After incubation of 2–10 days, the initial attack begins abruptly with chills, high fever, headache, and pains in muscles and joints, and lasts 2–8 days, ending by crisis. A remission period of 3– 10 days is followed by a relapse similar to the initial attack but milder. There may be 4–5 relapses, although occasionally 10 or more have been recorded. Mortality varies from 2 to 5% but may be considerably higher during epidemics.

Chlortetracycline is the most effective antibiotic drug, but penicillin, oxytetracycline, and streptomycin also have therapeutic value. See also Antibiotic.

The best way to prevent relapsing fever is to control louse and tick populations with effective insecticides and acaricides. See also Medical bacteriology; Pediculosis.

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.

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

Bibliography

Anonymous (2000). "Relapsing Fever." In Control of Communicable Diseases Manual, 17th edition, ed. I. Chin. Washington, DC: American Public Health Association.

Dworkin, M. S. et al. (1998). "Tick-Borne Relapsing Fever in the Northwestern United States and Southwestern Canada." Clinical Infectious Diseases 26: 122–131.

— DAVID T. DENNIS

For more information on relapsing fever, visit Britannica.com.

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