Brucellosis Transmission
Brucellosis is transmitted to humans primarily through ingestion of unpasteurized milk and dairy products, with additional routes including direct contact with infected animal tissues (especially reproductive materials) through broken skin, and inhalation of aerosolized bacteria. 1
Primary Transmission Routes
Food-Borne Transmission (Most Common)
The predominant route of human infection is consumption of contaminated unpasteurized milk or dairy products from infected livestock (cattle, sheep, goats, swine) 1, 2. This remains the leading cause globally and represents a critical public health concern in endemic regions 3, 4.
Occupational Direct Contact
High-risk groups include:
- Farmers, veterinarians, and abattoir workers: Infection occurs through direct contact between infected animal parts (particularly placentas and birth products) and cuts or abrasions in the skin 1
- Laboratory workers: At significant risk through inhalation of infected aerosolized particles during specimen processing 1, 2
- Marine mammal handlers: Emerging risk from contact with infected marine mammals, particularly during necropsies and aerosol-generating procedures 2
Contact with Reproductive Materials
Zoonotic transmission is particularly high during animal birthing, as infected animals shed massive numbers of organisms in reproductive fluids, aborted fetuses, and placentas 5, 6, 7. Live-birthing exhibits at agricultural fairs pose documented risks, especially in indoor settings with poor ventilation where organisms become aerosolized 5, 6.
Secondary Transmission Routes
Human-to-Human Transmission (Rare but Documented)
While uncommon, person-to-person transmission occurs through 8, 9:
- Vertical transmission: Transplacental infection and during delivery
- Breastfeeding: Documented transmission through breast milk 9
- Sexual transmission: Reported in isolated cases 8
- Blood transfusion and bone marrow transplantation: From infected donors 8, 9
- Aerosol from infected patients: Rare nosocomial transmission 8
Notably, 61% of human-to-human transmission cases involve infants <1 year old (newborns and breastfeeding infants) 8.
Critical Exposure Contexts
Agricultural Settings
- Petting zoos with birthing exhibits (Q fever and brucellosis risk) 5, 6
- Agricultural fairs where livestock are displayed 5, 6
- Hunting feral swine 2
Healthcare and Laboratory Settings
Laboratory-acquired infections remain prevalent due to:
- Inadequate biosafety practices 10
- Misidentification of Brucella species during routine processing 1
- Aerosol generation during specimen manipulation 2
Blood cultures require special laboratory precautions and prolonged culture up to 4 weeks 1.
Incubation Period
The incubation period ranges from 2-4 weeks, with documented cases up to 6 months 1, making exposure history assessment challenging.
Prevention Implications
For General Population
- Avoid unpasteurized dairy products, especially in endemic regions
- Avoid uncooked meat from potentially infected animals 11
For High-Risk Occupational Groups
- Use appropriate personal protective equipment, particularly respiratory protection during aerosol-generating procedures 2
- Implement multi-layered biosafety controls in laboratories 10
- Standard precautions during animal birthing events 5
For Healthcare Settings
- Consider brucellosis screening in tissue banks, transplants, and blood donations in endemic areas (though not yet standardized) 8
- Maintain awareness of nosocomial transmission risks 10
The convergence of occupational exposure, food safety lapses, and emerging zoonotic reservoirs (marine mammals) underscores that brucellosis transmission prevention requires coordinated veterinary-public health surveillance and strict adherence to food safety and occupational health protocols.