Vaccination with a live multi-gene deletion strain protects horses against virulent challenge with Streptococcus equi.

This research article discusses the development and testing of a new vaccine for Strangles – a frequently diagnosed infectious disease in horses caused by Streptococcus equi. The live vaccine showed potential in protecting horses from the virulent strain of the disease, even though some adverse reactions were observed.

Objective of the Study

• This study aimed to develop a new preventative vaccine for Strangles, a notorious and frequent infectious disease in horses caused by Streptococcus equi.
• The researchers hoped the new vaccine could offer improved efficacy and safety compared to existing options, potentially reducing the disease’s prevalence and impact on equine health.

Methodology

• A live vaccine strain of S. equi was generated, which contained deletions in six genes: sagA, hasA, aroB, pyrC, seM, and recA. The deletions aimed to reduce the virulence and increase the safety of the vaccine.
• This live vaccine strain was administered to nine Welsh mountain ponies via the intramuscular route. Four ponies developed adverse reactions after the first vaccination, and two were withdrawn from the study. The remaining seven ponies received a second vaccination.
• In contrast, a control group of nine ponies was injected with only culture media, and none developed adverse reactions.

Results and Findings

• On challenging the ponies with a virulent strain of S. equi, the seven vaccinated ponies did not develop any clinical signs of Strangles within eleven days post-challenge. Meanwhile, six of the nine control ponies did develop disease signs over the same period.
• At a post-mortem examination, a lymph node abscess was found in one of the seven vaccinated ponies, while all the control ponies had at least one lymph node abscess.
• Three of the six vaccinated ponies that were significantly protected from Strangles did not develop an adverse reaction following vaccination. This finding suggests that understanding the pro-inflammatory responses to S. equi could help develop a safer and more effective live attenuated vaccine for Strangles.

Conclusion

• The study concluded that the developed live vaccine strain shows promising results in protecting horses against the virulent strain of Strangles, even though there were some cases of adverse reactions.
• The authors suggest a further investigation into the pro-inflammatory responses to S. equi, which could lead to the development of a safer and more effective live attenuated vaccine. This vaccine could be safely administered through intramuscular injection, which would be a significant advancement in Strangles prevention.