Immunity to Streptococcus equi.

The research studies the immune response in horses to Streptococcus equi, tracked using various tests, over a period of 12 months post-vaccination. The study supports the idea of annual booster doses and concludes that immune response doesn’t last long after a natural infection.

Test Tools and Vaccination

• The research uses long chain test and occasionally bactericidal test as the two principal tools for measuring the horses antibody count. These tests were used to follow the response of horses’ immune system on vaccination against Streptococcus equi.
• High antibody levels were observed in serum samples after a full 3-dose immunisation course with a commercial vaccine. The long chain indices recorded were more than 5.0, which indicates a strong immune response.

Vaccine Efficacy and Booster Doses

• A major observation was a natural decline in the antibody titres 12 months after the full course suggesting that the effective immunity period of the vaccine is limited. This evidenced the need for yearly booster doses to maintain the horses’ resistance to the infection.

Natural Infection vs Vaccination

• Further, the research compared the immune response in horses during two Strangles (a disease caused by Streptococcus equi) outbreaks with the response after vaccination.
• Horses that had naturally recovered from the infection showed decreasing antibody levels 9 weeks post infection. This implies that the immune response does not last long after a natural infection, contrasting with the response post-vaccination.
• An interesting observation was that horses that initially had high levels of antibodies responded to vaccination. This could suggest that horses which have endured an infection may still benefit from being vaccinated.