Five Leptospira spp. Antibody Point-of-Care Tests in Healthy Dogs Reveal Different Results After Revaccination Against Leptospirosis

The microscopic agglutination test (MAT) is the diagnostic standard for canine leptospirosis. However, it is a time-consuming process and does not differentiate between infection- and vaccine-induced antibodies. Canine <i>Leptospira</i> spp.-specific antibody point-of-care (POC) tests provide the rapid detection of immunoglobulin M (IgM) and/or G (IgG). IgM POC tests are considered to become negative more rapidly after vaccination, making them more effective at diagnosing leptospirosis in not-recently vaccinated dogs. This study analysed 582 serum samples of 97 healthy dogs using five different POC tests and the MAT before vaccination and 2, 4, 12, 26, and 52 weeks afterwards. Among the POC tests, three detected IgM antibodies, one detected IgG antibodies, and one detected both IgM and IgG. The results were analysed using mixed-effects logistic regression. Before vaccination, only 2/291 IgM tests were positive (0.7%), compared to 45/194 IgG tests (23.2%). All the POC tests became positive after vaccination, but IgM positivity occurred significantly less frequently (59/1746), especially >4 weeks post-vaccination (7/59 positive results), with 94.5-99.6% specificity compared to 41.4-77.8% in IgG tests. These findings support the use of IgM POC tests in vaccinated dogs, while IgG POC tests are more difficult to interpret.