Three species of Brucella cause brucellosis in humans: Brucella melitensis, which infects goats; B. abortis, which infects cattle and, if the animal is pregnant, causes the spontaneous abortion of the fetus; and B. suis, which infects pigs. In animals, brucellosis is a self-limiting disease, and usually no treatment is necessary for the resolution of the disease. However, for a period of time from a few days to several weeks, infected animals may continue to excrete brucella into their urine and milk. Under warm, moist conditions, the bacteria may survive for months in soil, milk, and even seawater.
Because the bacteria are so hardy, humans may become infected with Brucella by direct contact with the bacteria. Handling or cleaning up after infected animals may put a person in contact with the bacteria. Brucella are extremely efficient in crossing the human skin barrier through cuts or breaks in the skin.