• Systemic granulomatous bacterial infection caused by Brucella sp. resulting in febrile illness; typically from ingestion of raw milk, unpasteurized milk, infected meat, or contact with secretions from infected animals
  • One of the most common worldwide zoonotic diseases
  • Incubation period usually 1 to 4 weeks but highly variable and may be several months
  • Often presents insidiously with many atypical or nonspecific features
  • Characterized by intermittent or irregular fevers and night sweats. Symptoms can range from subclinical disease to infection of almost any organ system.
  • Bone and joint involvement is common—20–40% (typically spondylodiscitis).
  • Disease may be recurrent, relapsing, or progress to chronic disease.
  • System(s) affected: cardiovascular, endocrine/metabolic, gastrointestinal, musculoskeletal, nervous, pulmonary, renal/urologic, skin/exocrine
  • Synonym(s): undulant fever; Malta fever; Mediterranean fever; Crimean fever; Bang disease

Pediatric Considerations

  • May be mild or subclinical
  • Boys infected more than girls (animal handling)
  • Children often present with refusal to walk or bear weight.
  • Children respond better to antibiotic treatment than do adults.

High rates of spontaneous abortion (can occur in subclinical cases). Early antibiotic treatment is preventive.


  • Predominant age: 20 to 45 years (occupational exposure); sometimes children (milk-related outbreaks); can occur at all ages
  • Predominant gender:
    • Male > female (occupational exposure)
    • Female ≥ male (milk exposure)


  • >500,000 new cases yearly (likely underreported)
  • <100 U.S. cases reported annually to the CDC


  • Common in developing countries; highest in Turkey, Syria, and Iran; some countries report case rates as high as 10/100,000; present in all inhabited continents
  • Highest rates in the United States are among Hispanic populations along U.S.–Mexico border; also Wyoming, North Carolina, Illinois, Florida, and Iowa
  • Reportable in all states

Etiology and Pathophysiology

  • Brucella ingestion from raw or undercooked tissue or unpasteurized milk products; susceptible to heat and disinfectant but can survive for weeks in frozen food and weeks to months in dust, soil, or water
  • Facultative intracellular parasite: gram-negative, nonmotile, non–spore-forming coccobacillus
  • Four species pathogenic to humans. Most virulent disease: Brucella melitensis, Brucella suis; also Brucella canis, Brucella abortus; can enter via mucous membrane or broken skin; occasionally inhaled
  • Laboratory workers at high risk of infection if specimens handled improperly
  • Person-to-person transmission is rare; sexual, vertical, (possibly) breast milk; blood transfusion
  • Potential airborne biologic weapon
  • Affects most domesticated ungulates (goats, cattle, camels, pigs, sheep), also wild bison and elk. Marine mammals also implicated in zoonotic transmission.
  • Infection increases abortion rate in animals, less so in humans.


  • Some evidence for intrauterine transmission; no reported birth defects
  • Some complications may have genetic predisposition.

Risk Factors

  • In the United States, occupational exposure to infected animals (cattle and sheep): veterinarians, meat processors, accidental exposure to vaccine, lab technicians, recent immigrants
  • Consumer exposure to unpasteurized dairy products and cheese
  • Travel to endemic countries (Mediterranean, Middle East, North and East Africa, Central Asia, India, Mexico, Central and South America)
  • Chronically ill and malnourished
  • Potential acceleration of HIV disease
  • Iron deficiency increases susceptibility.
  • Bison and elk are infected with brucellosis near Yellowstone Park.

General Prevention

  • Avoid infected, unpasteurized dairy products.
  • Use caution handling animal vaccines. Use protective goggles and protective gloves when handling tissue.
  • Human vaccine under investigation
  • Postexposure prophylaxis same as treatment

There's more to see -- the rest of this topic is available only to subscribers.