Immunisation of the equine uterus against Streptococcus equi subspecies zooepidemicus using an intranasal attenuated Salmonella vector.

This research tested the safety and effectiveness of a nebulised intranasal vaccine for preventing streptococcal uterine infections in horses. The vaccine uses an attenuated Salmonella vector to deliver a protective protein from a strain of Streptococcus equi subspecies zooepidemicus.

Objective and Methodology

• The researchers used an attenuated (or weakened) strain of Salmonella enterica serovar Typhimurium MGN707 as a delivery vector for the SzP protective protein from a serovar of Streptococcus equi subspecies zooepidemicus. The streptococcus strain is responsible for uterine infections in mares, a specific problem for the equine industry.
• The vaccine was delivered through nebulisation (using a device to create a fine spray) to the nasal passages of the mares.
• This study first conducted a preliminary investigation to assess the response to the vaccine by examining the serum, nasal, and uterine responses to the lipopolysaccharide of Salmonella Typhimurium in five vaccinated mares.

Findings and Observations

• In the main study, they compared the reactions of mares vaccinated with both the vector and the SzP-MB9 (the expressor group) and mares vaccinated with the vector only (the control group).
• The researchers identified a significant increase in the production of antibodies against SzP-MB9 in serum, nasal, and uterine washes in the mares from the expressor group compared to the control group, indicating that the vaccine was eliciting an immune response.
• All mares were assumed to be free of streptococci prior to being challenged with a high dose of Streptococcus equi subspecies zooepidemicus MB9 to test the effectiveness of the vaccine.
• Following the challenge, they found significantly fewer streptococci in the uterine flushings of the mares from the expressor group compared to the control group, showing the vaccine was effective in reducing the numbers of streptococci in the uterus.
• The only adverse reaction observed was a nasal haemorrhage in one mare, indicating the vaccine was generally well-tolerated.

Conclusion

• This research provides promising evidence that a nebulised intranasal vaccine can effectively protect against streptococcal uterine infections in mares.
• The protective efficacy of the vaccine was attributed to the presence of SzP-MB9 antibodies, conferred by the Streptococcus protein expressed by the weakened Salmonella vector used.