Bacteria

Brucellosis

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Brucellosis, Brucella abortus, Brucella suis, Brucella melitensis, Brucella canis

  • See Also
  1. Aerobic Gram Negative Rod
  • Epidemiology
  1. US Incidence <100 cases per year (0.34/100,000)
  2. More common outside the U.S.
    1. Unpasteurized milk
    2. Unimmunized livestock
  • Causes
  1. Brucella abortus (cows)
  2. Brucella suis (pigs)
  3. Brucella melitensis (goats, camels)
  4. Brucella canis (dogs)
  • Pathophysiology
  1. Brucella species
    1. Aerobic Gram Negative Rods
    2. Facultative Intracellular Parasite (within Macrophages)
    3. Species are named for their primary host
  2. Infection
    1. Humans acquire Brucella as a Zoonosis from direct contact with animals or animal products
      1. Infected animal meat (esp. sheep in U.S., or other unimmunized livestock)
      2. Cow, pig, goat or sheep exposure
      3. Aborted placenta
      4. Unpasteurized milk ingestion
      5. Live-Attenuated BrucellaVaccine exposure
    2. Transmission
      1. Enters via mucus membranes (Conjunctiva, GI Tract), broken skin, or inhalation
      2. No transmission person to person
      3. Infective dose: 10-100 organisms
  3. Pathogenesis
    1. Incubation: 5-60 days
    2. Brucella spreads via Lymph Nodes, where it is phagocytosed by Macrophages
    3. Brucella survives and multiplies within Macrophages as a Facultative Intracellular Parasite
    4. Hematogenous spread to distant organs
    5. Brucella species release Endotoxin when organism dies
  • Risk Factors
  1. United States Occupational Exposures
    1. Veterinarians
    2. Farm workers
    3. Meat processing plants
  2. Travel or residence in endemic region (via exposures to unpasteurized milk, unimmunized livestock)
    1. Mediterranean
    2. India
    3. North Africa, East Africa
    4. Central Asia, South Asia
  • Symptoms
  1. Intermittent Fevers
    1. Undulating fever (each evening)
    2. Temperature peaks in evening to 101-104
  2. Musculoskeletal (20-30%, up to 90% in some studies)
    1. Arthralgias
    2. Back pain (esp. sacroileitis)
  3. Weakness
  4. Lassitude
  5. Weight loss
  6. Headache
  7. Sweating
  8. Chills
  • Signs
  1. Hepatosplenomegaly (20-30%)
  2. Cervical or Inguinal Lymphadenopathy (12-20%)
  3. Orchitis or Epididymitis (2-40%)
  4. Purpura (5%)
  • Differential Diagnosis
  1. Tularemia
  2. Psittacosis
  3. Rickettsia
  4. Visceral Leishmaniasis
  5. Human Immunodeficiency Virus (HIV)
  • Complications
  1. Meningitis
  2. Endocarditis
  • Labs
  1. Culture (Slow growing, fastidious organism)
    1. Blood Culture (70% sensitive in acute illness)
    2. Discharge Culture
    3. Bone Marrow Aspirate (90% sensitive in acute illness)
  2. Complete Blood Count
    1. Thrombocytopenia
    2. Granulopenia
    3. Leukopenia with relative Lymphocytosis
    4. Anemia
  3. Brucella Serology (anti-Brucella antibodies)
  4. Brucella PCR
  5. Liver Function Tests (elevated in 30-60%)
  6. Bone Marrow Biopsy show Granuloma
  • Management
  • Non-Localized
  1. Precautions
    1. Risk of relapse in 10% of cases
    2. See other references for neurobrucellosis, Spondyloarthropathy and endocarditis
  2. Age <8 years old or pregnancy
    1. TMP-SMZ 5 mg/kg of TMP orally twice daily for 6 weeks AND
    2. Rifampin 15-20 mg/kg up to 600-900 mg orally daily for 6 weeks
  3. Age >8 years old and adults
    1. Doxycycline 100 mg orally twice daily for 6 weeks AND
    2. Gentamicin 5 mg/kg IV daily for 7 days AND
    3. Consider Rifampin 15-20 mg/kg up to 600-900 mg orally daily for 6 weeks
      1. May be used in place of Gentamicin
      2. For Spondyloarthropathy or Arthritis, use all 3 agents, with Rifampin with Doxycycline for 3 months
        1. Alternatively Ciprofloxacin 750 mg twice daily AND Rifampin for 3 months may be used
      3. When combined with Doxycyline and Gentamicin improves clearance rates without relapse
        1. Vrioni (2014) Antimicrob Agents Chemother 58:7541-4 [PubMed]
  • Prevention
  1. See other references for Post-exposure Prophylaxis
  2. Food safety practices (e.g. Milk pasteurization)
  3. Hand Hygiene in those handling animals or animal products
  4. Livestock Vaccination
  • Course
  1. Weeks to months of symptoms
  • Prognosis
  1. Case Fatality <5% treated
  • References
  1. (2023) Sanford Guide to Antibiotics, IOS app accessed 2/8/2025
  2. (1998) Medical Management of Biological Casualties
    1. U.S. Army Medical Research Institute of ID
  3. Qureshi (2023) Ann Med 55(2):2295398 +PMID: 38165919 [PubMed]