Brucella abortus RB51 in milk of vaccinated adult cattle

• No B. abortus was recovered from any tested milk of post-partum vaccinated cows.
• Only one milk sample was faintly positive for RB51 by PCR.
• Consumption of milk from cows vaccinated with RB51 in post-partum may not pose a public health risk.

The aim of this study was to evaluate the shedding of Brucella abortus in the milk of cows vaccinated with a full dose of RB51 during lactation. Eighteen cows, nine previously vaccinated with S19 as calves and nine non-vaccinated, were immunized subcutaneously with 1.3 × 1010 CFU of B. abortus RB51, 30–60 days after parturition. Milk samples from all animals were collected daily until day 7, and at weekly interval for the next 9 weeks after vaccination. To evaluate the shedding of B. abortus, milk samples were submitted for culture and PCR. No B. abortus was isolated from any sample tested. Only one sample, collected on first day after vaccination from a cow previously vaccinated, was faintly positive in the PCR. In conclusion, the public health hazard associated with milk consumption from cows vaccinated with RB51 in post-partum is very low, despite vaccination with the full dose and regardless of previous S19 vaccination.

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