Seroprevalence and Antibody Magnitude of Brucella canis in Shelter Dogs: A Four-Year Study in Southern Italy

Background: Brucella canis is an emerging zoonotic pathogen responsible for canine reproductive disorders and public health concerns. This study assessed the seroprevalence of B. canis in dogs from Campania, Southern Italy (2022–2025). Methods: Serum samples (n = 400) were retrospectively screened using an indirect immunofluorescence assay (IFAT), performed according to the manufacturer’s instructions. Screening was conducted at a 1:40 cut-off, followed by serial dilutions to determine endpoint titres. Statistical analysis included chi-square tests for univariable screening, followed by nominal logistic regression models to evaluate the association between IFAT positivity and predictive factors (year, province, and sex of dogs). Additionally, a general linear model (GLM) was applied to the seropositive subset (n = 69) to analyse the magnitude of the antibody response, expressed as geometric mean titres (GMTs). Results: The overall seroprevalence was 17.3% (95% CI: 13.6–21.0%). Dog’s sex, year of sampling, and province were not significant independent predictors of infection (p > 0.05), but GLM analysis showed that sampling year (p = 0.0024) and province (p = 0.0490) significantly influenced antibody intensity. A significant temporal increase in antibody intensity was observed towards 2025 (p = 0.037), suggesting an intensification of infection pressure. Conclusions: Our results confirm that Brucella canis is an endemic pathogen in the shelter dog population of southern Italy. The high seroprevalence and significant increase in antibody magnitude (GMT) over the study period indicate rising infection pressure, highlighting the urgent need for mandatory screening and a coordinated One Health surveillance strategy to manage zoonotic risk effectively.