Vaccine potential of novel surface exposed and secreted proteins of Streptococcus equi.

This research aimed to test the efficacy of surface exposed or secreted proteins of the bacteria Streptococcus equi as potential vaccine components against equine strangles, a highly infectious disease affecting horses’ head and neck lymph nodes. Unfortunately, the horses that were immunized produced strong antibody responses but did not resist Streptococcus equi upon exposure, suggesting that an effective strangles vaccine needs to stimulate the clearance of the bacteria from the tonsils, rather than the production of serum antibody.

Research Purpose and Methodology

• The primary goal of the study was to investigate the effectiveness of new secreted or surface-exposed proteins of the Streptococcus equi bacteria as vaccine components to tackle equine strangles, an infectious lymphadenitis disorder.
• The proteins were singled out through an expression gene library created using sera from resistant horses.
• Proteins produced by Streptococcus equi but not its ancestor Streptococcus zooepidemicus were chosen for the vaccine trial.

Vaccination Trial

• The researchers performed vaccination on two separate groups of ponies.
• The first group of eight ponies was vaccinated with six proteins expressed uniquely by the Streptococcus equi strain CF32, and not by the ancestral strain Streptococcus zooepidemicus 631.
• The second group was immunized with five adhesin and other proteins encoded by genes belonging to Linkage Group 1.

Vaccine Response and Analysis

• The ponies in both groups returned strong serum antibody responses to each protein when evaluated with Enzyme-Linked Immunosorbent Assay (ELISA), demonstrating the effectiveness of the vaccines in eliciting an immune reaction.
• However, none of the ponies exhibited resistance to the Streptococcus equi CF32 strain when directly exposed to the bacteria following vaccination.

Study Conclusions

• The study’s results corroborated with earlier proofs that horses, once recovered from the bacterial infection, could quickly clear intranasally inoculated Streptococcus equi from their bodies.
• Moreover, they did not present any detectable serum antibody responses to the bacteria’s surface proteins, complicating the conventional vaccine development approach.
• Thus, the research suggests that an effective vaccine against equine strangles should stimulate immune-mediated tonsillar clearance rather than boosting the production of serum antibody.