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Brucellosis is a worldwide zoonosis of wild and domestic animals and is most commonly found in countries of the Mediterranean basin, the Arabian Gulf, the Indian subcontinent, and parts of Mexico and Central and South America. Human infections are caused by four species: Brucella melitensis which is the most common infection in the United States and is acquired from goats and sheep, B abortus, B suis, and B canis. The organisms are intracellular gram-negative coccobacilli that infect humans by ingestion, inhalation, or inoculation of the skin or conjunctivae.1,2 In countries where brucellosis is endemic, the most common risk factor for infection is consumption of unpasteurized milk.2-4 The typical patient seen in the United States tends to be an Hispanic male from California or Texas who acquired B melitensis from contaminated goat’s milk or goat cheese that was imported from or ingested in Mexico. Brucellosis can be an occupational hazard for veterinarians and other individuals involved in the livestock industry. This changed markedly with immunization of herds and improved sanitation in meat-processing plants so that infections ascribable to B abortus (cattle) and B suis (swine) have essentially disappeared. Brucellosis is rare in the United States and is infrequently seen in children. In 2006, only 14 of 121 cases reported to the Centers for Disease Control were in patients under age 15.5

Clinical Manifestations

Brucellosis is a disease of protean manifestations. Symptoms typically develop 2 to 3 weeks after exposure and can be acute or insidious. Fever is an almost invariable component of the illness and may wax and wane over a prolonged period of time in untreated patients, hence the name, undulant fever. The classical triad of brucellosis consists of fever, arthralgia or arthritis, and organomegaly, often associated with night sweats, malaise, weight loss, and anorexia. Physical examination findings may be scarce and include joint tenderness, splenomegaly or hepatomegaly, and rarely arthritis.4,6,7 Congenital brucellosis has been described, and the infection can be transmitted via breast milk.8,9 The illness spectrum varies from mild febrile illness to major systemic disease with endocarditis, meningitis, arthritis, or osteomyelitis. The disease is sometimes localized to a single organ, such as the musculoskeletal, pulmonary, cardiovascular, or neurologic systems.1


A definitive diagnosis of brucellosis is made when the agent is isolated from blood, bone marrow, or other fluid cultures. The serologic diagnosis is typically made using the serum agglutination test (SAT), which should demonstrate a 4-fold or greater rise in titer or be positive at dilutions of 1:160 or greater10 or less commonly by an enzyme immunoassay.11 In the United States, both tests use B abortus as the antigen, and the titers reported are based on cross-reactions. Of note is that these assays do not detect antibodies to B canis. Brucella titers tend to fall during treatment, and ...

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