The serological response of foals to vaccination against strangles.

The research studied the response to strangles vaccination in 100 foals, comparing a commercial bacterin and autogenous vaccine, and tracking various blood serum states before, during, after vaccination and after infection. They observed that healthy foals achieved the highest immune response within one to two months after vaccination, which persisted for 120 days, while those foals who developed strangles had lower initial responses but rose significantly after recovery.

Study Participants and Experimental Setup

• The study involved 100 foals who were given either a commercial bacterin or an autogenous vaccine, both targeting the Streptococcus equi bacterium causing strangles, a prevalent infectious disease in horses.
• The researchers monitored the foals over time, recording their states as prevaccination, during vaccination, postvaccination, and postinfection, where applicable.
• In a minor part of the study, four ponies were given a formalinized Str. equi bacterin vaccination and exposed to the bacterium to observe their infection and recovery.

Observations and Findings

• Throughout the study, the researchers gauged the foals’ serological response (immune response in the bloodstream) by conducting passive haemagglutination and long chain tests.
• In healthy foals, peak immune response was observed one to two months postvaccination. This period included a mean passive haemagglutination titre (an indicator of antibody concentration) of 6.78 and long chain indices (another measure of response) of 4.41.
• These high levels persisted for 120 days postvaccination, indicating sustained antibody production and immunity in the subjects.
• However, foals which developed clinical strangles had lower passive haemagglutination titres (3.78) one to two months after immunization. These levels, though, rose significantly after the foals recovered from strangles.
• The experiment involving the four ponies indicated a partial protection against strangles infection after immunization with formalinized Str. equi bacterin. Like before, passive haemagglutination titres, long chain indices and the capability to kill the bacterium were highest at 35 days postvaccination. These values, however, did not increase after the ponies were infected.