Contrasting roles of farm categories in the enzootic circulation of bovine brucellosis through cattle trade in Paraguay.

Bovine brucellosis leads to significant economic losses in enzootic regions due to infertility, abortion, weak calves, and reduced milk and meat production. In humans, this zoonotic disease often results in a chronic, debilitating illness. In Paraguay, where cattle farming is an important sector of the economy, bovine brucellosis remains enzootic all over the country. We developed a within- and between-farm stochastic model to assess the potential of the female trade network in sustaining country-wide transmission of bovine brucellosis and to identify the roles of different farm categories in its transmission. A national serosurvey and cattle trade data were used to estimate the intra-farm transmission parameters, and the effective reproduction number R at the country and farm levels. Results showed that replacement heifer trade sustained transmission among farms. Country-level R was 1.06 (95 % HDI: 0.23-2.19), suggesting a dynamic close to the epidemiological equilibrium, which is consistent with the history of bovine brucellosis in this country. Farm category analysis revealed that R ranged from 0.14 to 2.00 with the lowest values observed in small farms and the highest in large farms, indicating that small farms contributed little to brucellosis transmission, medium farms had a neutral impact and large farms played a major role. Disease persistence was mainly driven by within-region transmission, with large farms facilitating spread between regions. These findings highlighted the need for region- and farm-category control strategies to effectively manage bovine brucellosis. The model implemented in this work gave valuable insights into the bovine brucellosis dynamics in Paraguay and could be used to test different control approaches.