Spatial heterogeneity in exposure to Brucella suis and pathogenic leptospires in feral pigs across New South Wales

Feral pigs (Sus scrofa) are important reservoirs for zoonotic and livestock pathogens in Australia, but robust information on the spatial distribution of pathogens in pig populations remains limited. We analysed serological data from a systematic, state-wide surveillance program to investigate spatial heterogeneity in exposure to Brucella suis and pathogenic leptospires in feral pigs across New South Wales (NSW). Samples were collected from 2548 feral pigs at 81 locations between 2022 and 2026 and tested for antibodies to B. suis, L. interrogans serovars Pomona (hereafter Pomona) and Hardjo, L. borgpetersenii serovar Tarassovi and Coxiella burnetii. Bayesian spatial models were used to predict the probability of B. suis and Pomona seropositivity across the state in relation to feral pig relative abundance, generating spatial risk surfaces directly relevant to animal and human health management. Survey-wide adjusted seroprevalence was 0.16 for B. suis, 0.52 for Pomona, 0.06 for Hardjo and 0.05 for Tarassovi. Brucella suis exposure was concentrated in the north-eastern quadrant of NSW and strongly positively associated with local feral pig density (derived from expert opinion), whereas exposure to Pomona was widespread but locally variable. Seroprevalences of Hardjo and Tarassovi were spatially restricted, and antibodies to C. burnetii were rarely detected. By combining structured state-wide sampling with spatial modelling, this study provides probabilistic inference on pathogen exposure. The results demonstrate how systematic surveillance can provide actionable spatial information for One Health risk management, prioritising risk-based surveillance, assessing confidence in pathogen absence and supporting management responses for endemic, emerging, or exotic animal diseases.