Leptospira seroprevalence in dogs, cats and horses: the effect of cross-reactivity between serovars and vaccination status on seroprevalence estimates

In this study, we estimated the Leptospira seroprevalence in dogs (n = 376), horses (n = 88), and cats (n = 169) using Microscopic Agglutination Test (MAT) against 12 Leptospira serovars. We observed a Leptospira seroprevalence of 29.41%, 47.73%, and 12.35% in dogs, horses, and cats, respectively. The highest seroprevalence was observed for serovar Autumnalis (74.55%) in dogs, and Bratislava in horses (95.24%) and cats (42.86%). We found a significant level of potential cross-reactivity between multiple Leptospira serovars tested, with highest cross-reactivity to serovar Autumnalis in dogs. The dogs that were vaccinated against Leptospira had a significantly higher seroprevalence (45.92%) compared to unvaccinated dogs (16.28%; p < 0.001). A significant difference in seroprevalence was observed in vaccinated and unvaccinated dogs to all four serovars included in the canine vaccine (p < 0.001). Among the diagnostic samples submitted from 2021-2023, 40% (103/252) of the canine serum samples were positive by MAT, with the highest positivity rate for the serovar Autumnalis. On Leptospira PCR, 10.7 % (35/325) urine samples and 5.8% (15/257) blood samples were positive. Our study findings show evidence of Leptospira exposure and potential disease in the study area. The cross-reactivity between the Leptospira serovars used in the MAT and vaccination status may also overestimate the levels of exposure.