What is the etiology of brucellosis?

Etiology of Brucellosis

Brucellosis is a zoonotic infection caused by bacteria of the genus Brucella, with B. melitensis being the most pathogenic species in humans, followed by B. suis and B. abortus. 1

Causative Organisms

The disease is caused by gram-negative, facultative intracellular coccobacilli of the Brucella genus, which currently includes multiple species: 2, 3

• Primary human pathogens:

  • Brucella melitensis - the most common and virulent cause of human disease worldwide 1, 2
  • B. abortus - causes milder disease, prevalent in North America and Europe 2, 4
  • B. suis - second most pathogenic species 1, 3
  • B. canis - causes rare but persistent human infections 1, 2

• Emerging pathogens:

  • Novel Brucella species from marine mammals (B. pinnipedialis, B. ceti) have been identified as causes of human disease 1
  • Additional species include B. ovis, B. neotomae, B. microti, and B. inopinata 3

Transmission Routes

The most common route of transmission is ingestion of unpasteurized milk products from infected animals. 1, 5

Direct transmission pathways:

• Consumption of contaminated dairy products - unpasteurized milk, cheese, and other dairy from infected sheep, goats, cattle 1, 2
• Direct contact - infection through cuts or abrasions when handling infected animal parts (particularly placenta) 1, 3
• Inhalation - aerosolized particles in laboratory settings or during necropsy procedures 1
• Penetration through damaged skin or conjunctiva when handling infected animals 3

Animal Reservoirs

The natural reservoir and source of human infection are infected domestic and wild animals: 1, 3

• Primary reservoirs: Sheep, goats, cattle, deer, elk, pigs, dogs 1
• Marine mammals: Harbor porpoises and other marine species can harbor Brucella species 1
• Wildlife populations: Various wild animals serve as reservoirs 3

High-Risk Populations

Certain occupational groups face elevated exposure risk: 1, 3

• Veterinarians and veterinary technicians 3
• Farmers and cattlemen working on multi-herd farms 3
• Abattoir workers and meat processing employees 1, 3
• Laboratory workers handling Brucella specimens 1
• Insemination service employees and zoo technicians 3
• Individuals handling stranded marine mammals or performing necropsies 1

Geographic and Epidemiologic Considerations

Brucellosis represents an index of poor socioeconomic status and is re-emerging as a significant cause of travel-related disease. 1

• The disease is endemic in regions with unpasteurized dairy consumption and inadequate veterinary care 1, 6
• In the United States, there has been an upsurge of B. melitensis cases associated with unpasteurized goat's milk or cheese from Mexico 2
• The disease occurs on all inhabited continents and remains the commonest anthropozoonotic infection worldwide 1, 3

Common Pitfalls

• Laboratory safety: Brucella specimens require special handling precautions, as laboratory-acquired infections can occur through aerosol exposure 1
• Marine mammal exposure: The increase in marine mammal strandings has increased human exposure risk to Brucella species, requiring appropriate personal protective equipment during handling 1
• Occupational exposure: Failure to use respiratory protection during aerosol-generating procedures (such as necropsies) necessitates costly antimicrobial prophylaxis and prolonged monitoring 1