Brucellosis is a contagious, costly disease of ruminant animals that also affects humans. Although brucellosis can attack other animals, its main threat is to cattle, sheep and goats, and swine. It can also affect wildlife. Considering the damage done by the infection in animals such as decreased milk production, weight loss in animals, loss of young, infertility, and lameness, it is a serious disease of livestock. The rapidity with which it spreads and the fact that it is transmissible to humans emphasizes the serious nature of the disease.

The disease is caused by a group of bacteria known scientifically as the genus Brucella. Three species of Brucella cause the most concern: B. abortus, principally affecting cattle; B. suis, principally affecting swine; and B. melitensis, affecting sheep and goats. Bacteria are shed in milk or via the aborted fetus, afterbirth, or other reproductive tract discharges.