Development of evidence-based strategies to control Brucella spp. in dairy herds in Henan Province, China : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Epidemiology at Massey University, Manawatu, New Zealand

Abstract

Brucella spp. remains a significant challenge in China, affecting the dairy industry and public health despite decades of voluntary control measures. This thesis aims to address key knowledge gaps in diagnosis, epidemiology, and disease impact of Brucella spp. in dairy herds to inform evidence-based control strategies in Henan Province, China. A scoping review of 61 studies (2004-2022) characterized the epidemiological landscape, revealing that B. abortus biovar 3 predominated 85.8% of Brucella spp. isolates recovered from dairy cattle in China. Considerable heterogeneity was observed in prevalence estimates and Brucella spp. isolation across provinces. These findings guided subsequent investigations into diagnostic accuracy, biosecurity practices, disease impact, and financial analyses. To enhance diagnostic accuracy, a cross-sectional study evaluated the diagnostic performance of four serological tests in Henan dairy herds. Using a novel Bayesian latent class model, optimal cut-off values were established for fluorescence polarization assay and competitive ELISA, estimating test sensitivity (69.7%-89.9%) and specificity (97.1%-99.6%). These findings provide a foundation for improving brucellosis diagnostic strategies. Beyond diagnosis, an assessment of farm biosecurity practices and stakeholder motivations was conducted using a structured questionnaire. Two distinct clusters of dairy herds were identified. Cluster 1, characterized by medium (400-1000) to large (>1000) herd sizes and higher educational levels, showed better adherence to proper biosecurity practices than Cluster 2. Stakeholders prioritized disease impacts and economic losses, highlighting the need for integrating these into the brucellosis control programs. To address this knowledge gap about disease impact, a longitudinal study estimated the effects of Brucella seroconversion on key production indicators. The annual incidence of seroconversion of brucellosis was 13.1% (95% CI: 10.9, 15.6) at the cow level. Seroconverted cows exhibited a reduction in daily milk yield (3.2 kg/day, 95% CI: 2.4, 4.0), elevated somatic cell counts, and increased pregnancy loss (relative risk: 4.26, 95% CI: 3.17, 5.73), compared to that of consistently negative cows. These findings provided essential epidemiological insights into the seroconversion of Brucella spp. and its implications on three essential dairy productivity outcomes. Building on these epidemiological insights, a financial analysis estimated the direct annual costs of Brucella infection at 78.9 Chinese Yuan (CNY) per animal and 4,019 CNY per infected cow. Among the three evaluated interventions (vaccination, test-and-culling, and test-and-culling plus vaccination), vaccination was the most cost-effective, yielding a benefit-cost ratio of 5.84 (95% CI: 4.34 – 7.42) and a net present value of 408.2 thousand CNY over ten years. Overall, this thesis integrates epidemiological, diagnostic, biosecurity, and financial analyses to inform evidence-based brucellosis control in Henan dairy herds. These findings could support farm stakeholders and policymakers in improving the control of Brucella spp. in Henan dairy herds, contributing to broader brucellosis control efforts in China.