CDC Investigation of Brucella abortus RB51 Infection Linked to Pennsylvania Dairy

A case of Brucella abortus RB51 infection in 2018 was traced back to a Pennsylvania dairy, raising concerns about the risk of infections from drinking raw milk.

Joann Gruber, PhD, MSPH

The case, detailed in a recent Morbidity and Mortality Weekly Report, involved a New York patient who contracted brucellosis from the live attenuated vaccine strain of B. abortus used to prevent brucellosis in cattle.

“Until relatively recently, we thought the potential for Brucella abortus RB51 infections in humans only occurred in very limited settings (e.g., needlesticks among veterinarians),” Joann Gruber, PhD, MSPH, an epidemiologist with the US Centers for Disease Control and Prevention (CDC), told Contagion^®. “However, there have now been three documented cases of brucellosis caused by Brucella abortus RB51 linked to consumption of unpasteurized milk since 2017.”

A case of brucellosis in Texas in July 2017 was linked to a Texas dairy, and a second case was identified in October 2017 in New Jersey. The Pennsylvania dairy associated with the third case distributed milk to 19 states, and health officials notified public health veterinarians in those states. The CDC launched an investigation of exposure to the Brucella abortus RB51 strain last year. No other cases of brucellosis were identified.

The MMWR investigators noted that whole-genome sequencing identified two distinct RB51 strains shed by a single cow at the Pennsylvania dairy, one of which matched the patient’s isolate. The cow, which had received the vaccine in 2011 and was purchased by the dairy in 2016, was taken out of production. Subsequent bulk milk samples tested negative for the pathogen.

The Pennsylvania dairy had a herd of 30 cows, 16 of which were born at the dairy, which did not provide RB51 vaccination. The cow that tested positive for the RB51 strains was one of 14 born outside of the dairy. This was the first time isolation of different strains of the pathogen from different quarters of a cow’s udder has been reported.

Along with the risk of brucellosis—which causes fever, osteoarticular symptoms, sweating, and constitutional symptoms and can become chronic and life threatening if not treated—drinking raw milk also carries risk of infection from other pathogens, such as Campylobacter, Escherichia coli, and Salmonella.

“We want to prevent infections by making sure people understand the risk of serious infections when consuming unpasteurized milk,” Gruber said “We will also continue to look for any new Brucella abortus RB51 infections.”

The CDC lists Brucellosis among the top 8 zoonotic diseases of most concern in the United States.