Streptococcus equi subsp. equi (Strangles) Infection
Authors: Taylor Sandra D., Wilson W. David
Journal: Clinical Techniques in Equine Practice
Summary
# Editorial Summary: Streptococcus equi subsp. equi Vaccination Research Researchers evaluated a recombinant S protein (Ssee) vaccine candidate for *Streptococcus equi* subsp. *equi* by immunising 20 Quarter Horses with three doses of either 200 or 400 µg at weeks 0, 4, and 12, whilst measuring antibody responses in serum and nasal secretions via ELISA and functional assays over 28 weeks, alongside serological testing of 78 naturally infected horses. Vaccinated horses mounted significantly elevated serum and nasal IgG responses lasting up to 12 weeks post-final dose and demonstrated enhanced complement deposition onto the pathogen, though opsonophagocytic killing remained unimproved; notably, horses with clinical strangles developed minimal serum anti-Ssee IgG titres. The S protein's ability to trigger robust functional antibody responses while failing to appear in naturally infected animals suggests potential utility as a DIVA (differentiate infected from vaccinated animals) marker alongside immunological protection. For equine practitioners, this work indicates S protein warrants further development as a vaccine to mitigate strangles severity and enable serological distinction between vaccinated and infected horses—a critical advantage for herd management and disease surveillance protocols.
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Practical Takeaways
- •Ssee vaccination generates functional antibodies that enhance complement-mediated immune responses, potentially reducing strangles severity, though natural infection does not produce comparable antibody responses
- •The differential antibody response between vaccinated and infected horses enables serological differentiation (DIVA strategy), useful for disease surveillance and export testing
- •Nasal secretory IgA was not induced by vaccination, suggesting mucosal immunity may require alternative vaccine formulations or delivery routes to enhance upper respiratory protection
Key Findings
- •Immunization with recombinant S protein (Ssee) significantly increased serum and nasal IgG antibodies for up to 12 weeks after the third vaccination (P < 0.05)
- •Vaccinated horses developed significantly greater complement deposition onto Ssee compared to controls (P < 0.001), but did not develop opsonophagocytic killing activity
- •Horses naturally infected with strangles failed to develop high levels of serum IgG against S protein, unlike vaccinated horses
- •S protein vaccine shows potential to differentiate between vaccinated and naturally infected horses using serological testing