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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
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Clinical Manifestations
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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
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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 a persistently ...