Brucellosis

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. ^[1]
  • 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
    • Brucella suis: mainly affects (feral and domestic) pigs and reindeer, but also cattle and bison
    • Brucella canis: affects dogs
• Transmission: zoonotic ^[2]
  • 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
• General
  • Flu-like symptoms
  • Night sweats
  • High, potentially undulant fever
  • Painful lymphadenopathy
• Localized infection
  • Arthralgias, low back pain → osteoarticular infection (e.g., osteomyelitis, spondylitis)
  • Epididymal and testicular tenderness, flank pain → genitourinary infection (e.g., epididymo-orchitis, pyelonephritis)
  • Murmurs, friction rubs, tachycardia → cardiac infection (e.g., endocarditis, myocarditis)

Brucellosis manifests as UNdulant fever and the causative pathogen is transmitted by UNpasteurized dairy products.

References: ^[3]

• Laboratory studies: may show anemia, neutropenia, mild elevation of liver enzymes
• Serology: serum agglutination (Rose Bengal test), ELISA
• Confirmatory test
  • Blood culture (may be false negative)
  • Lymph node or bone marrow biopsy specimen and culture
    • Histopathology: noncaseating granulomas
    • Culture medium for isolation: charcoal yeast extract agar (cysteine and iron buffered)

References: ^[3]

• Antibiotic therapy ^[4]
  • First-line therapy: doxycycline PLUS rifampin
  • Second-line therapy: doxycycline PLUS streptomycin

• Obligation to report: Brucellosis is a nationally notifiable disease.

1. Humans and Brucella Species. https://www.cdc.gov/brucellosis/clinicians/brucella-species.html. Updated: November 12, 2012. Accessed: October 31, 2020.
2. Brucellosis: Transmission. https://www.cdc.gov/brucellosis/transmission/index.html. Updated: November 12, 2012. Accessed: April 10, 2017.
3. Brucellosis. https://rarediseases.org/rare-diseases/brucellosis/. . Accessed: October 31, 2020.
4. CDC - Brucellosis treatment. https://www.cdc.gov/brucellosis/treatment/index.html#:~:text=Generally%2C%20the%20antibiotics%20doxycycline%20and,allergic%20to%20doxycycline%20or%20rifampin. . Accessed: October 9, 2020.
5. Herold G. Internal Medicine. Herold G ; 2014