Brucellosis is caused by the bacterium brucella. It normally infects people by spreading from one of its many animal reservoirs. The most common animal reservoirs are cattle, pigs, goats, sheep, and rarely dogs. This disease has been eliminated from domestic animal populations in the United States. However, it periodically infects this population after exposure to wildlife, such as wild pigs. The bacteria can spread from animals to people in three main ways:
- Direct contact. Transmission occurs through direct contact (breaks in the skin or mucosal surfaces) with infected animal tissue, blood, urine, vaginal excretions, aborted fetuses, or placentas.
- Unpasteurized dairy products. Transmission can also occur from the ingestion of raw milk and dairy products (unpasteurized) that came from an infected animal,
- Inhalation. When individuals breathe in bacteria that are in the air.
Person-to-person transmission is rare, but has been documented.