Titers to Leptospira species in horses in Alberta

Sera from horses in Alberta, submitted to Agriculture and Agri-Food Canada for routine testing for equine infectious anemia from January 1987 to June 1989, were tested for antibody against 13 serovars of pathogenic Leptospira spp., using the microscopic agglutination test. The purpose of the study was to investigate the prevalence of serum titers to those serovars in horses in Alberta, and to analyze the associated risk factors. Descriptive statistics were compiled and logistic regressions were computed. Titers to L. interrogans serovars icterohaemorrhagiae, bratislava, copenhageni, and autumnalis were common (94.6%, 56.6%, 46.5%, and 43.5%, respectively). The prevalence of titers to other serovars ranged from 0.8% to 27.2%. Age was almost always significantly associated with the presence of titers. In general, the chances of being seropositive rose by approximately 10% with each year of life. Horses managed individually (eg, track horses) were approximately half as likely to be seropositive as were horses managed in groups (eg, rodeo horses).