Serological responses of Sport horses pre- and post-third vaccination with Strangvac

Background: Strangles, caused by Streptococcus equi, is an endemic disease of horses throughout the world. A vaccine against strangles, Strangvac, is available in Europe, but there are no published serological data following the revaccination of Sport horses. Objectives: To measure the antibody response of Sport horses to the components of Strangvac before and after third vaccination. Study Design: Longitudinal cohort study. Methods: Adult Sport horses were administered their third vaccination with Strangvac at 5 months (group 1, n=20) or 12 months (group 2, n=15) after second vaccination. Horses were monitored closely for adverse signs. Blood samples were collected from both groups immediately before and 14 days after third vaccination to quantify antibody responses by ELISA. Results: Transient signs of mild injection site swelling in 8.5 % horses for 2 days, and a temperature rise of ~0.8 oC in most horses for 1 day, occurred post-vaccination. Health status returned to normal within 48 hours. The antibody titres to the vaccine components were 3.34±0.31 and 3.14±0.29 before third vaccination and increased significantly to 3.90±0.29 and 3.90±0.17 after third vaccination in groups 1 and 2, respectively (P<0.0001 for both groups). Main limitations: Data and samples from a matched unvaccinated control group were unavailable. Conclusions: Strangvac was safe and a revaccination program after 5 or 12 months was equally efficient for the vaccination of Sport horses.