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Brucella abortus RB51 Persistent Infection and Milk Shedding in Vaccinated Dairy Cattle: A Public Health Risk
Elizabeth S Hines1, Sara F Margrey2, Stephanie W Cox3
1Virginia-Maryland College of Veterinary Medicine, Blacksburg, Virginia, USA.
Zoonoses and Public Health
|August 14, 2026
Summary
Cattle vaccinated with the RB51 Brucella strain can shed the bacteria in milk years later, causing human brucellosis. Raw dairy consumption poses a significant risk, necessitating a re-evaluation of RB51 vaccine use.
Area of Science:
- Veterinary Medicine
- Zoonotic Disease Research
- Food Safety
Background:
- Brucellosis is a zoonotic disease caused by Brucella bacteria, posing a public health threat.
- The RB51 strain vaccine is widely used for cattle brucellosis but carries risks for human exposure.
Purpose of the Study:
- To investigate the shedding of RB51 strain Brucella in the milk of vaccinated dairy cattle.
- To determine the link between RB51 shedding in cattle and human brucellosis cases.
Main Methods:
- Retrospective review of NVSL records.
- Identification of RB51 Brucella in milk via culture, PCR, and whole genome sequencing (WGS).
Main Results:
- Six dairy cattle vaccinated with RB51 shed the bacteria in their milk as adults.
- Two of these cattle were linked to three human brucellosis cases.
- Human cases resulted from consuming unpasteurized dairy products.
Conclusions:
- Milk-borne RB51 Brucella from vaccinated cattle can cause human brucellosis.
- Consumption of raw dairy products from RB51-vaccinated cows poses a health risk.
- Critical evaluation of RB51 vaccine use and vaccination practices is recommended.
