The research on purification of brucellosis in dairy farm based on stochastic model

Brucellosis is one of the most prevalent zoonotic diseases in China, with the number of human cases increasing annually since 2019. In 2022, the Chinese government explicitly incorporated “purification and elimination” into the guidelines and requirements for animal epidemic prevention under the Animal Epidemic Prevention Law. Aligning with the national strategy that prioritizes farms as the starting point for brucellosis purification and gradually extends efforts to regional levels, we focus on dairy cattle farms as the research subject and establish a stochastic model by using continuous-time Markov Chains to analyze the spread of brucellosis. Based on the fitting results of monitored positive data from two scaled breeding farms, the model is applied to calculate the control reproduction number, the distributions of epidemic duration, and the final scale of infected individuals. The findings indicate that under purification measures (monthly quarantine and culling), the estimated purification period for these farms ranges from 4 to 8 months, with a final infection scale of 65–87%. Furthermore, considering the implications and practical significance of prevention and control measures, we adopt the final epidemic size as an evaluation criterion to conduct sensitivity analysis. This allows us to estimate the final infection rate based on varying breeding scales and initial infection proportions, thereby determining the threshold for the initial infection proportion across different breeding scales. This threshold serves as a critical indicator for deciding whether additional purification measures are necessary. The research findings of this study provide valuable theoretical support and practical guidance for the implementation of brucellosis purification efforts.