Specific antibody in the equine genital tract following local immunisation and challenge infection with contagious equine metritis organism (Taylorella equigenitalis).

The research conducted assesses the immune response in horses to local vaccination and subsequent infection with the organism that causes contagious equine metritis (Taylorella equigenitalis), a sexual disease. The findings revealed that while local vaccination prompts a detectable immune response, it does not prevent infection upon exposure to the disease.

Immunisation and Antibody Response

• The study attentively examined the levels of specific antibodies in serum, uterine, and vaginal secretions of horses following local immunisation and experimental infection with the contagious equine metritis (CEM) organism.
• The investigated immune response involved intrauterine immunisation with deactivated / killed T. equigenitalis, this vaccination approach induced a systemic IgG antibody response alongside localised IgA and IgM responses in the uterus.

Challenge Infection and Antibody Response

• Upon subsequent exposure to the active CEM organism, the researchers noted a strong metritis (inflammation of the uterus) effect in both control and vaccinated horses, indicating that immunisation does not seem to prevent infection.
• However, this challenge infection escalated the levels of antibodies in both serum (blood) and secretions beyond the levels observed post-immunisation, suggesting a more dramatic immune response to actual infection.
• This escalated response was observed to be limited to IgA and IgM antibodies and was seen in both uterine and vaginal secretions. Conversely, there was no notable increase in local IgG antibodies, though an increase was detected in serum IgG levels post-challenge infection.

Second Challenge Infection

• Upon a second exposure to the active metritis organism, after the initial infection had naturally resolved and a period of re-vaccination had been provided, observations suggested a reduced severity of clinical symptoms and lower bacteria isolation rates from both vaccinated and control horses.
• Regrettably, this second exposure did not provide absolute protection from infection for any of the experimental subjects, underscoring the challenge of developing effective vaccine measures against this sexually transmitted equine disease.

The results of this research point to the complexity of immune response and the difficulty of vaccine development against sexually transmitted diseases like contagious equine metritis. They suggest future exploration could focus on understanding the factors contributing to vaccine efficacy and disease resilience in horses.