Investigation of the prevalence of Brucella antibodies and field strains in immunized dairy herds in Lingwu, Ningxia

Abstract

Abstract Background Brucella 19 strain vaccines are widely used to prevent brucellosis in cattle. The vaccine antibodies are generally acknowledged to persist for less than 12 months after immunization. The real rate of persistent antibodies may be a difference because of different feeding management and immunization schedules. The effect of vaccine immunization and the correlation between the persistence of antibodies induced by immunization and field strain infection remains unclear in the northwest of China. Results We revealed that Brucella A19 vaccine antibodies persist in dairy herds for more than 12 months. We established a PCR method for identifying both Brucella A19 and non-A19 strains, resulting in the detection of 10 field strains of Brucella abortus from vaginal swab samples collected from 1,537 dairy cows. We analyzed the rates of seropositivity and herd seropositive rates in dairy cattle in Lingwu City from 2021 to 2023. By employing a mathematical expectation strategy, we completed testing of 1537 samples after conducting only 306 tests of pools of six samples, thereby reducing the workload by 80.1%. Conclusion We propose that the detection of antibodies in cattle vaccinated with the A19 vaccine more than 12 months previously should not be solely relied upon as a diagnostic basis for brucellosis, and it is essential to combine this approach with PCR analysis to specifically identify field strains. Timely detection of Brucellain aborting livestock was identified as an efficient strategy for diagnosis. This research provides valuable data for the prevention and control of brucellosis in immunized cattle herds, as well as serving as a reference method for investigating and diagnosing brucellosis in livestock vaccinated in other regions.