Bovine Brucellosis

Last Modified: April 01, 2025
Close-up of brown cattle herd.

Brucellosis (also known as contagious abortion or Bang's disease) is a costly disease of livestock and wildlife. It is caused by a group of bacteria in the genus Brucella. The disease has significant consequences for animal health, public health, and international trade.

Brucellosis occurs mainly in cattle, bison, and swine, but can affect other animals (cervids, goats, sheep, and horses) and people.

In cattle and bison, the bacteria of concern is Brucella abortus. It has been present in the United States since the 1930s. A longstanding national eradication program mostly eliminated the disease in U.S. cattle. Today, only occasional spillover cases occur in cattle and other livestock near the Greater Yellowstone Area (GYA). Wild bison and elk in the GYA are the last remaining reservoir of this disease in the United States.

When signs do appear, they're most obvious in pregnant animals. Here's what to look for:

  • Abortion (usually at 5–7 months of pregnancy)
  • Birth of weak, unhealthy calves
  • Decreased milk production
  • Weight loss
  • Poor conception rates or infertility
  • Retained afterbirths with resulting uterine infections
  • Enlarged, arthritic joints (occasionally) 

Note: Appearance alone isn't an effective way to detect brucellosis. Infected animals may appear healthy, even during pregnancy. However, they can still harbor and spread infectious bacteria and serve as dangerous sources of infection.

On rare occasions, humans have been infected with brucellosis, usually by drinking unpasteurized milk from infected cows or by contact with infected birthing fluids and tissues. Visit the Centers for Disease Control and Prevention online for human health information about brucellosis.

Report Signs of Animal Disease

Producers or owners who suspect an animal disease should contact their veterinarian to evaluate the animal or herd. Find an accredited veterinarian.

Animal health professionals (veterinarians; diagnostic laboratories; public health, zoo, or wildlife personnel; and others) report diagnosed or suspected cases of nationally listed reportable animal diseases to APHIS Area Veterinarians in Charge and to the State animal health official as applicable under State reporting regulations. 

Controlling Brucellosis