(Goossens et al. 1983; Ruben et al. 1991). Brucellosis probably is endemic in Afghanistan, but data on its occurrence there are sparse.
Between 100 and 200 US cases of human brucellosis were reported annually to CDC during the 1990s. Brucellosis cases in the United States have begun to shift from people who are occupationally exposed to animals and animal products (such as butchers, abattoir workers, veterinarians, and farmers) to people who ingest unpasteurized goat-milk products imported from Latin America (Chomel et al. 1994; Taylor and Perdue 1989). The disease is 8 times more prevalent at the US-Mexico border than elsewhere in the United States (Doyle and Bryan 2000; Fosgate et al. 2002). In the United States, cattle-associated B. abortus has been the etiologic agent of human brucellosis acquired directly from animals, and B. melitensis the agent of human brucellosis acquired from dairy products (CDC 1986; Spink 1954).
The acute form of human brucellosis is usually manifested 2-4 weeks after infection as a nonspecific febrile illness accompanied by profuse sweating, headache, malaise, arthralgia, arthritis, myalgia, back pain, or a combination of these. Hematologic abnormalities may include anemia, leukopenia, thrombocytopenia, and clotting disorders that are usually mild and resolve with therapy (Crosby et al. 1984; Pappas et al. 2004). Severe thrombocytopenia is rare (Young et al. 2000). Brucellosis in animals (especially that caused by B. abortus) is associated with spontaneous abortion. Although brucellosis may result in human abortion, it may be no more common than abortion that occurs during any infectious process (Khan et al. 2001; Makhseed et al. 1998).
The diagnosis of brucellosis should be considered in the appropriate clinical setting with appropriate demographic risk factors. Laboratory analysis may disclose mild leukopenia, thrombocytopenia, and anemia with minimally to moderately abnormal liver-function tests. Definitive diagnosis involves recovering organisms, usually from blood or bone marrow. Culturing of bone marrow is the most sensitive method of diagnosis (Gotuzzo et al. 1986). In rare cases, brucellae may also be recovered from synovial fluid, cerebral spinal fluid, urine, or biopsy samples (Gotuzzo et al. 1986). Rapid automated bacterial identification systems may occasionally misidentify brucellae, for instance, as Moraxella phenylpyruvica (Roiz et al. 1998). PCR and other molecular techniques may be used, but they are not yet used widely in clinical settings (Colmenero et al. 2002; Fox et al. 1998; Morata et al. 2001; Queipo-Ortuno et al. 1997). If microbiologic cultures are negative, diagnosis of human brucellosis usually involves serologic analysis.
A number of serologic tests for diagnosing brucellosis exist (Al Dahouk et al. 2003; Young 1991). The most widely used is a serum agglutination test (SAT), which measures IgM and immunoglobulin G (IgG) brucella antibody titers. SAT titers above 1:160 are diagnostic for brucellosis in the appropriate clinical setting (Young 1991). A 2-merceptoethanol assay can increase the specificity of the SAT by distinguishing IgG from IgM responses (Baldi et al. 1996). Drawbacks of the SAT include cross-reactivity and inability to diagnose B. canis infection. In some people with brucellosis, an SAT response will not occur. Blocking antibodies may be present, or a Coombs test may be positive (Pascual et al. 1988). An enzyme-linked immunosorbent assay (ELISA) specific for brucella has higher sensitivity and specificity than the