Brucellosis is caused by Brucella abortus (cattle), B. melitensis (sheep and goats), B. suis (pigs) and B. canis (dogs). Infection occurs when someone comes into contact with the body fluids of an infected animal (blood, placenta, urine, fetuses), by consumption of raw (unpasteurized) dairy products and in some instances, by airborne transmission of the pathogen in animal pens, laboratories and slaughter houses.
There is no substantial evidence to suggest person-to-person spread occurs.