A retrospective serological study on Leptospira spp. exposure and Brucella canis in dogs from Croatian animal shelters

Abstract

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. Anti-Leptospira antibodies were detected by the microscopic agglutination test (MAT) using a panel of 10 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 frequently detected serovars were Icterohaemorrhagiae (64.1%), Australis (60.2%), Canicola (43.7%), Pomona (38.3%), and Grippotyphosa (24.2%). After excluding potentially vaccine-induced titers to Icterohaemorrhagiae and Canicola in recently vaccinated dogs, Australis, Pomona, and Grippotyphosa became the predominant serovars. Most antibody titers were low to moderate, consistent with previous exposure rather than acute infection. No antibodies against Brucella canis were detected in any of the 375 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 serovars associated with wildlife and rodent reservoirs highlights the need for continued surveillance, rodent control, and careful interpretation of serology in relation to vaccination history.