Sources of Brucella Infection
The primary sources of human Brucella infection are consumption of unpasteurized dairy products, direct contact with infected animal tissues, and inhalation of contaminated aerosols, with domestic livestock serving as the main reservoir hosts. 1
Animal Reservoirs
Brucella species primarily infect domestic animals that serve as reservoir hosts:
- Cattle, goats, sheep, swine, camels, buffalo, and dogs are the most common animal reservoirs worldwide 2
- Marine mammals including harbor porpoises, seals, and cetaceans harbor specific Brucella species (B. ceti and B. pinnipedialis) and represent an emerging source of human infection 1
- Various Brucella species affect deer, elk, pigs, and other wildlife 1
Primary Transmission Routes to Humans
Food-Borne Transmission
- Consumption of unpasteurized milk and dairy products is the most common transmission route globally 1, 3, 4
- Infected animal products remain a significant source in endemic regions 2
Direct Contact Transmission
- Contact with infected animal tissues through breaks in skin or mucous membranes during handling of livestock, birthing products, or carcasses 2, 4
- Hunting activities, particularly hunting feral swine, represent a significant exposure risk in the United States 1
- Handling of stranded marine mammals or performing necropsies without proper respiratory protection 1
Aerosol Transmission
- Inhalation of aerosolized particles during procedures involving infected tissues, particularly during aerosol-generating procedures like bone cutting with electric saws 1
- Laboratory-acquired infections among workers handling Brucella specimens, making it the most frequent laboratory-acquired bacterial infection 5
Geographic and Epidemiologic Context
- Brucellosis is uncommon in the United States with an average of 113 human cases reported annually during 2000-2009 1
- The disease remains endemic in many parts of the world, particularly in regions with unpasteurized dairy consumption and close livestock contact 1, 3
- Neurobrucellosis is more prevalent in endemic regions where exposure to livestock and unpasteurized dairy is common 3
Less Common Transmission Routes
While rare, human-to-human transmission has been documented through:
- Placental transmission to newborns 6
- Breastfeeding 6
- Sexual transmission 6
- Blood transfusion and bone marrow transplantation 6
Critical Prevention Considerations
Common pitfalls in exposure prevention include:
- Failure to use respiratory protection during necropsies or aerosol-generating procedures on potentially infected animals, which necessitates costly 24-week monitoring and prophylactic antimicrobials 1
- Inadequate personal protective equipment when handling marine mammals, which has led to documented exposures requiring intensive follow-up 1
- Laboratory workers handling unknown diagnostic samples without proper BSL-3 precautions until Brucella is identified 1