Brucellosis is a bacterial disease caused by Brucella, typically transmitted to humans from infected unpasteurized animal milk, or direct contact from an infected animal. It causes a systemic illness including fever, and inflammation of the brain, testicles, and heart. Human to human transmission is rare, and documented to have occurred via sexual contact, pregnancy and breastfeeding.
The US Centers for Disease Control recommends not breastfeeding if mother is infected with brucellosis.
Tuon FF, Gondolfo RB, Cerchiari N. Human-to-human transmission of Brucella- a systematic review Trop Med and Int Health 22(5) May 2017 p. 539-546
US Centers for Disease Control https://www.cdc.gov/brucellosis/ (8/15/2021)