Brucellae are small, gram-negative, unencapsulated, nonsporulating, nonmotile rods or coccobacilli that can persist intracellularly. The genus Brucella includes four major clinically relevant species: B. melitensis (acquired by humans most commonly from sheep, goats, and camels), B. suis (from swine), B. abortus (from cattle or buffalo), and B. canis (from dogs).
Brucellosis is transmitted via ingestion, inhalation, or mucosal or percutaneous exposure; the disease in humans is usually associated with exposure to infected animals or their products in either occupational settings (e.g., slaughterhouse work, farming) or domestic settings (e.g., consumption of contaminated foods, especially dairy products). The global prevalence of brucellosis is unknown because of difficulties in diagnosis and inadequacies in reporting systems.
Regardless of the specific infecting species, brucellosis often presents with one of three patterns: a febrile illness similar to but less severe than typhoid fever; fever and acute monoarthritis, typically of the hip or knee, in a young child (septic arthritis); or long-lasting fever, misery, and low-back or hip pain in an older man (vertebral osteomyelitis).
An incubation period of 1 week to several months is followed by the development of undulating fever; sweats; increasing apathy and fatigue; and nonspecific symptoms such as anorexia, headache, myalgias, and chills.
Brucella infection can cause lymphadenopathy, hepatosplenomegaly, epididymoorchitis, neurologic involvement, and focal abscess.
Given the persistent fever and similar symptoms, tuberculosis is the most important differential diagnosis (Table 94-1).
TABLE 94-1Radiology of the Spine: Differentiation of Brucellosis from Tuberculosis ||Download (.pdf) TABLE 94-1 Radiology of the Spine: Differentiation of Brucellosis from Tuberculosis
| ||BRUCELLOSIS ||TUBERCULOSIS |
|Site ||Lumbar and others ||Dorsolumbar |
|Vertebrae ||Multiple or contiguous ||Contiguous |
|Diskitis ||Late ||Early |
|Body ||Intact until late ||Morphology lost early |
|Canal compression ||Rare ||Common |
|Epiphysitis ||Anterosuperior (Pom’s sign) ||General: upper and lower disk regions, central, subperiosteal |
|Osteophyte ||Anterolateral (parrot beak) ||Unusual |
|Deformity ||Wedging uncommon ||Anterior wedge, gibbus |
|Recovery ||Sclerosis, whole-body ||Variable |
|Paravertebral abscess ||Small, well-localized ||Common and discrete loss, transverse process |
|Psoas abscess ||Rare ||More likely |
Laboratory personnel must be alerted to the potential diagnosis to ensure that they take precautions to prevent occupational exposure.
The organism is successfully cultured in 50–70% of cases. Cultures using the BACTEC system usually become positive in 7–10 days and can be deemed negative at 3 weeks.
PCR analysis of blood or tissue samples is more sensitive, faster, and safer than culture.
Agglutination assays for IgM are positive early in infection. Single titers of ≥1:160 and ≥1:320 are diagnostic in nonendemic and endemic areas, respectively.