Leptospira seroprevalence in dogs, cats, and horses in Tennessee, USA.

We estimated the Leptospira seroprevalence in dogs, cats, and horses from Tennessee, USA, using the microscopic agglutination test (MAT) against 12 Leptospira serovars. We observed Leptospira seropositivity in 110 of 374 (29.4%) dogs, 21 of 170 (12.4%) cats, and 42 of 88 (47.7%) horses. The highest seroprevalence was observed for serovars Autumnalis (74.6%) in dogs, and Bratislava in cats (42.9%) and horses (95.2%). We found a significant level of potential cross-reactivity between multiple Leptospira serovars tested, with highest cross-reactivity to serovar Autumnalis in dogs. Leptospira seroprevalence was significantly higher in vaccinated dogs (45 of 98 [46%]) compared to unvaccinated dogs (14 of 86 [16%]; p < 0.001). A significant difference in seroprevalence was observed in vaccinated and unvaccinated dogs to all 4 serovars included in canine leptospiral vaccines (p < 0.001). We also evaluated the Leptospira testing results from our diagnostic laboratory submissions from 2021-2023; 103 of 252 (40%) canine serum samples were positive, with the highest positivity rate for serovar Autumnalis. On Leptospira real-time PCR, 35 of 325 (10.7%) urine samples and 15 of 257 (5.8%) blood samples were positive. The cross-reactivity between the Leptospira serovars used in the MAT and vaccination status should be considered when estimating seroprevalence.