Brucellosis is a zoonotic infection caused by different species of Brucella, a genus of gram-negative bacteria. The most common vectors of the disease are cattle, sheep, goats, and pigs. Transmission occurs through the ingestion of contaminated animal products, contact with infected animals, or inhalation of bacteria. Although brucellosis is a major public health concern in many countries, it has become rare in the United States as a result of animal health policies. Brucellosis manifests with flu‑like symptoms. However, hepatomegaly, splenomegaly, lymphadenopathy, and focal organ infection (e.g., osteomyelitis, endocarditis, spondylitis) may also occur. Recommended treatment is a combined regimen of doxycycline and rifampin.
Pathogen: Brucella spp. are facultative intracellular, gram-negative, aerobic, coccobacilli. 
- Brucella melitensis: mainly affects sheep, goats, and camels → Malta fever
- Brucella abortus: mainly affects cattle, but also bison, deer, and elk → Bang disease
- Rare causes of disease in humans
Transmission: zoonotic 
- Contaminated food, esp. raw meat, unpasteurized dairy products
- Contact with infected animals
- Risk factors: occupational or recreational exposure to infected animals and animal products (e.g., farmers, veterinarians, hunters, slaughterhouse workers, laboratory personnel)
- Pathophysiology: Brucella spp. survive and replicate within macrophages of the reticuloendothelial system → formation of noncaseating granulomas
- Incubation period: 1–3 weeks
- Localized infection
- Laboratory studies: may show anemia, neutropenia, mild elevation of liver enzymes
- Serology: serum agglutination ( ), ELISA
- Confirmatory test
- Obligation to report: Brucellosis is a nationally notifiable disease.