Tracing the invisible: Spatial patterns of swine brucellosis in wildlife and domestic pigs of northeast Portugal.

The interface between wild boar and domestic pigs represents is a critical hotspot for the spillover and spillback of several diseases, including brucellosis. This cross-sectional study assessed the seroprevalence of Brucella spp. and B. suis in swine at the wildlife-livestock interface in northeast Portugal, focusing on wild boar and the autochthonous Bísaro pig breed. Antibodies against Brucella spp. were detected in 25.7 % of wild boar (95/370; 95 % CI: 21.2 %-30.1 %) and 15.2 % of Bísaro pigs (35/231; 95 % CI: 10.5 %-19.8 %). Among these, 82 wild boar and 33 domestic pigs tested positive for B. suis, with molecular confirmation in three domestic pigs, marking the first molecular identification of B. suis in Bísaro pigs. Spatial analysis revealed distinct B. suis prevalence, higher in wild boar in the northwest and in domestic pigs in the southeast. A significant positive correlation between the spatial distributions suggests potential transmission at the wildlife-livestock interface. Environmental and anthropogenic factors showed moderate correlation with B. suis prevalence, suggesting a link to animals' overpopulation. Additionally, prevalence was positively associated with pig farms land elevation and negatively with dense shrublands coverage/areas, reinforcing the role of farming practices in pathogen spillover. These findings highlight the multifactorial nature of B. suis distribution, shaped by both ecological and human-driven landscape features. Given the zoonotic potential, this study underscores the urgent need for integrated One Health surveillance and control strategies to mitigate public health risks in rural communities and safeguard animal and human health at both regional and national level.