Description

• 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.

Epidemiology

• 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)

Incidence

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

Prevalence

• 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.

Genetics

• 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