Retrospective serological study on Leptospira spp. exposure and brucella canis in dogs from Croatian animal shelters

This retrospective cross-sectional study investigated exposure to Leptospira spp. and Brucella canis in dogs housed in two animal shelters in Croatia. Archived serum samples from 375 dogs from the Dumovec shelter (Zagreb County) and the Friends Čakovec shelter (Međimurje County) were tested. Specific antibodies against Leptospira were detected by the microscopic agglutination test (MAT) using a panel of ten pathogenic serovars, while B. canis antibodies were screened using a rapid immunochromatographic assay. Associations with shelter, sex, age, serovar distribution, and antibody titers were statistically evaluated. Overall, 128/375 dogs (34.1%) were seropositive to at least one Leptospira serovar. Seropositivity was 29.6% in Dumovec and 36.1% in Čakovec, with no significant difference between shelters. No significant association was found between overall seropositivity and sex or age. Before adjustment for recent vaccination, the most frequent MAT reactions were directed against antigens representing Icterohaemorrhagiae, Australis, Canicola, Pomona, and Grippotyphosa. In a vaccination-related sensitivity analysis, MAT reactivity to antigens representing Australis, Pomona, and Grippotyphosa remained frequent, although this pattern should be interpreted cautiously because complete vaccine-product information was not consistently available. Most antibody titres were low to moderate, more consistent with previous exposure rather than with acute infection. No antibodies against B. canis were detected in any samples. These findings indicate substantial environmental exposure of shelter dogs in Croatia to pathogenic leptospires and support their role as sentinels of zoonotic risk. The predominance of MAT reactivity patterns associated with serogroups linked to wildlife and rodent reservoirs highlights the need for continued surveillance, rodent control, and careful interpretation of serology in relation to vaccination history.