Clinical Information

Brucellosis is a major disease in humans and domesticated animals and is a systemic bacterial infection caused by gram-negative coccobacilli of the genus Brucella. Brucellosis is a zoonotic disease, and a variety of domestic animals serve as reservoir species: Brucella infects goats (Brucella melitensis), cattle (Brucella abortus), swine (Brucella suis), and dogs (Brucella canis). Transmission to humans results from direct contact with infected animals, exposure to infectious aerosols, or ingestion of unpasteurized dairy products; human-to-human transmission does not occur. While few cases are reported in the US, the majority of cases occur in the Mediterranean region, Western Asia, and parts of Latin America and Africa.

Three species of Brucella commonly cause disease in humans: B melitensis, B suis, and B abortus. Clinical manifestations of brucellosis consist of fever, sweats, malaise, weight loss, headache, and weakness. The onset may be insidious or acute, generally beginning within 2 to 4 weeks after exposure. Any organ or system of the body may be involved, although death is uncommon. Presumptive diagnosis of brucellosis can be made by detection of high or rising titers of specific antibodies, typically to smooth lipopolysaccharide (S-LPS), a major antigenic virulence determinant. Serologic tests using S-LPS can detect antibody to the three major Brucella species due to this shared epitope. IgM antibodies appear during the first week of infection followed by a switch to IgG synthesis during the second week. A variety of serologic tests have been used for diagnosis of Brucella infection. Detection of anti-Brucella antibodies using enzyme-linked immunosorbent assay (ELISA) has been demonstrated to be a sensitive diagnostic approach. However, all specimens testing positive by ELISA should be confirmed by an agglutination method as a means to increase assay specificity.