RELAPSING FEVER

infectious disease characterized by recurring fever symptoms and caused by spirochetes that have been given a number of conflicting genus and species designations: Borrelia (Treponema) recurrentis (obermeieri, duttoni, et al.). The spirochetes are transmitted from one person to another by lice of the genus Pediculus and from animals to humans by ticks of the genus Ornithodoros. The human disease has a sudden onset with violent febrile symptoms, which persist for about a week in cases contracted from lice and usually for a shorter period in the tick-transmitted disease. The attack ends by a crisis with profuse sweating, after which the patient is fairly well until, about a week later, febrile symptoms return. Additional relapses may followrarely more than one or two in the louse-borne disease but up to 12 (usually decreasing in severity) in cases contracted from ticks. The mortality is variable, ranging from nil in some tick-transmitted varieties to 6 percent or as high as 30 percent in some louse-borne epidemics associated with famine conditions. The spirochetes may invade the central nervous system and cause a variety of usually mild neurological symptoms. Relapsing-fever spirochetes were the first microscopic organisms to be associated clearly with serious human disease. The German bacteriologist Otto Obermeier observed these organisms in the blood of relapsing-fever patients in 186768 and published his observations in 1873. They are easily seen in dark-field microscopic preparations of the patient's blood collected during the height of the febrile attack but disappear from the blood during the intervals between attacks. These observations, as well as the relapsing symptoms, have been related to changes in the immunological (antigenic) characteristics of the spirochetes, which cause each attack and relapse. As the patient develops immunity to the prevailing immunological type and recovers from the attack, a new (mutant) immunological type of the spirochete develops and produces the relapse. Because neither the bite nor the excreta of the louse is infectious, human infections usually result from crushing the louse on the skin while scratching. The adult ticks may live and remain infectious for as long as five years without feeding. The spirochetes frequently invade the eggs of infected female ticks and survive in the body of the developing larvae and nymphs. All developmental stages of the tick, therefore, may transmit the infection by bite or otherwise. Penicillin and other antibiotics have proved effective against the disease. Inadequate therapy commonly results in relapse after treatment, probably because of the persistence of live spirochetes in the brain, where the drug concentration does not reach curative levels. After treatment these protected spirochetes may reinvade the bloodstream.