A case study investigating the effects of emergency vaccination with <i>Brucella abortus</i> A19 vaccine on a dairy farm undergoing an abortion outbreak in China

Yu Wang; Yan Wang; Qingjie Peng; Zhijie Xiang; Yingyu Chen; Guiqiang Wang; Xijuan Wu; Aizhen Guo; Ian D. Robertson

doi:10.1186/s44149-022-00056-6

Animal Diseases ›› 2022, Vol. 2 ›› Issue (1) : 24. DOI: 10.1186/s44149-022-00056-6

Original Article

A case study investigating the effects of emergency vaccination with Brucella abortus A19 vaccine on a dairy farm undergoing an abortion outbreak in China

Yu Wang¹^,²^,³^,⁴ ,
Yan Wang¹^,²^,³^,⁴ ,
Qingjie Peng¹^,²^,⁵ ,
Zhijie Xiang¹^,² ,
Yingyu Chen¹^,²^,³^,⁴^,⁶ ,
Guiqiang Wang⁷ ,
Xijuan Wu⁷ ,
Aizhen Guo¹^,²^,³^,⁴^,⁶^,^h ,
Ian D. Robertson¹^,²^,³^,⁴^,⁸^,^j

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Abstract

Brucellosis is an important zoonosis that results in substantial economic losses to the livestock industry through abortions and reduced milk yield. This study investigated an abortion outbreak in a dairy herd and then explored the effects of emergency vaccination with Brucella abortus A19 vaccine on the incidence of abortion and milk yield. A full dose of vaccine (6 × 10¹⁰—12 × 10¹⁰ colony forming units, CFU) was administered subcutaneously to calves and non-pregnant heifers, and a reduced dose (6 × 10⁸—12 × 10⁸ CFU) to adult cows and pregnant replacement heifers. Rose Bengal Test was used to screen Brucella infection status and then positive samples were tested with a C-ELISA. Animals that tested positive for both tests were considered positive to Brucella spp. The animal-level seroprevalence of brucellosis was 23.1% (95% CI: 17.0, 30.2), and the attributable fraction of abortions in seropositive animals was 89.1% (95% CI: 64.3, 96.7). The odds of seropositivity were significantly higher in cows that aborted compared to cows that calved normally (OR = 21.4, 95% CI: 4.4, 168.4). Cows in sheds A2 and C1 were 10.2 (95% CI: 1.4, 128.0) and 17.0 (95% CI: 2.8, 190.3) times more likely to be seropositive than cows in shed B1. Antibodies were not detectable in most heifers 12 months post-vaccination. The effectiveness of the vaccine in preventing abortions was estimated to be 56.8% (95% CI: 15.8, 77.8) for the entire herd, but increased to 86.7% (95% CI: 4.4, 98.1) when only primiparous heifers were considered. Furthermore, a significant increase in the average herd 305-day milk yield one-year after vaccination was also observed relative to that in the previous three years. It is concluded that emergency vaccination of a dairy herd undergoing an abortion outbreak with the A19 vaccine effectively reduced the incidence of abortion and indirectly increased milk yield one-year after vaccination.

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Yu Wang, Yan Wang, Qingjie Peng, Zhijie Xiang, Yingyu Chen, Guiqiang Wang, Xijuan Wu, Aizhen Guo, Ian D. Robertson. A case study investigating the effects of emergency vaccination with Brucella abortus A19 vaccine on a dairy farm undergoing an abortion outbreak in China. Animal Diseases, 2022, 2(1): 24 https://doi.org/10.1186/s44149-022-00056-6