BRUCELLOSIS : CLINICAL ASPECTS
Brucellosis starts with malaise, chills, and fever 7 to 21 days after infection. Drenching sweats in the late afternoon or evening are common, as are temperatures in the range of 39.4 to 40°C. The pattern of periodic nocturnal fever (undulant fever) typically continues for weeks, months, or even 1 to 2 years. Patients become chronically ill with associated body aches, headache, and anorexia. Weight loss of up to 20 kg may occur during pro-longed illness. Despite these dramatic effects, physical findings and localizing signs are few. Less than 25% of patients show detectable enlargement of the reticuloendothelial organs, the primary site of infection. Of such findings, splenomegaly is most common, followed by lymphadenopathy and hepatomegaly. Occasionally, localized infection devel-ops in the lung, bone, brain, heart, or genitourinary system. These cases usually lack the pronounced systemic symptoms of the typical illness.
Definitive diagnosis requires isolation of Brucella from the blood or from biopsy specimens
of the liver, bone marrow, or lymph nodes. Supplementation with carbon dioxide is needed for growth of B. abortus. The slow growth of some strains requires prolonged incubation of culture medium to achieve isolation. Blood cultures may require 2 to 4 weeks for growth, although most are positive in 2 to 5 days. The diagnosis is often made serologically but is subject to the same interpretive constraints as are all serologic tests. Antibodies that agglutinate suspensions of heat-killed organisms typically reach titers of 1:640 or more in acute disease. Lower titers may reflect previous disease or cross-reacting antibodies. Titers return to the normal range within a year of successful therapy.
Tetracyclines are the primary antimicrobics for the treatment of brucellosis. Doxycycline is preferred because of its pharmacologic characteristics. In seriously ill patients, streptomycin, gentamicin, or rifampin may be added. Although _-lactams are active in vitro, clinical response is poor, probably due to failure to reach the intracellular location of the bacteria. The therapeutic response is not rapid; 2 to 7 days may pass before patients become afebrile. Up to 10% of patients have relapses in the first 3 months after therapy.
Prevention is primarily by measures that minimize occupational exposure and by the pasteurization of dairy products. Control of brucellosis in animals involves a combination of immunization with an attenuated strain of B. abortus and eradication of infected stock. No human vaccine is in use.
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