Humans are generally infected with brucellosis in one of three ways:
Eating undercooked meat or consuming unpasteurized/raw dairy products
The most common way to be infected is by eating or drinking unpasteurized/raw dairy products. When sheep, goats, cows, or camels are infected, their milk becomes contaminated with the bacteria.
If the milk from infected animals is not pasteurized, the infection will be transmitted to people who consume the milk and/or cheese products.
Breathing in the bacteria that cause brucellosis (inhalation)
Breathing in the bacteria that causes brucellosis may also lead to infection. This risk is generally greater for people in laboratories that work with the bacteria. In addition, slaughterhouse and meat-packing employees have also been known to be exposed to the bacteria and ultimately become infected.
People who hunt animals may also be at risk. When they are in contact with infected animals, exposure to the bacteria may occur through:
- skin wounds
- accidentally ingesting undercooked meat
- inhaling the bacteria while dressing their game. Commonly infected animals include: bison, elk, caribou, moose and wild hogs (feral swine).
Person-to-person spread of brucellosis is extremely rare. Infected mothers who are breast-feeding may transmit the infection to their infants. Sexual transmission has been rarely reported. While uncommon, transmission may also occur via tissue transplantation or blood transfusions.