Humoral Response in Naturally Exposed Horses After Leptospiral Vaccination

Leptospirosis causes substantial economic losses in horses. Nevertheless, humoral response postvaccine is not well described and there is a paucity of knowledge regarding the dynamics of the response in naturally infected horses under field conditions. Fifty-four randomly selected mares, 36 vaccinated (group I) and 18 nonvaccinated (II-control), were used. Mares in group I were given two doses of a multivalent (12 antigens) commercial vaccine (D0 and booster on D40). Blood samples were collected (for microscopic agglutination test and enzyme-linked immunosorbent assay) at D0, D7, D14, D21, D30, D60, and D90. Vaccination significantly interfered with the production of antileptospiral antibodies. Seroreactivity increased rapidly, but was of short duration (up to D60). Responses varied among serogroups present in the vaccine, with the most intense responses against those serogroups that were previously circulating in the herd (Icterohaemorrhagiae and Australis). Therefore, we concluded that vaccines elicited a significant humoral response in horses.