Strangles, convalescent Streptococcus equi subspecies equi M antibody titers, and presence of complications.

This study focuses on how the severity of Streptococcus equi subspecies equi infection or strangles in horses can be tracked through the measurement of M protein antibody titers. It suggests that higher levels of these antibodies could be a potential marker for predicting complications in horses affected by strangles.

About the Study

• This research was conducted based on 48 horses all from the same farm that were involved in a strangles outbreak.
• The study was clinical and observational in nature, and the researchers monitored S. equi M protein (SeM) antibody titers in all the horses at 8 weeks after the infection.
• Some horses were also chosen to have their titers measured at 12 and 28 weeks post-infection.
• The horses were grouped into different categories based on their disease status: no disease, uncomplicated strangles, persistent guttural pouch (GP) infection, or complicated cases that involved metastatic abscesses, purpura hemorrhagica, secondary infections, and dysphagia. Each category was then compared to the antibody titer measurements.

Key Findings

• The study found that more than half (58%) of the horses displayed signs of S. equi infection. From this group, 39% had uncomplicated strangles, 21% had persistent GP infection, and 18% were complicated cases.
• Approximately 33% of the total horses (16 out of 48) were found with SeM antibody titers of ≥1:12 800 eight weeks after infection.
• Further, out of the horses with high antibody titers, just over one third, 6 out of 16, had visible complications. Furthermore, about three-quarters of the horses with complications, specifically 6 out of 8, had antibody titers ≥1:12 800.
• The sensitivity of an SeM antibody titer ≥1:12 800 for detecting complications was 75% with a 95% confidence interval, which was higher than the specificity (43%; with a 95% confidence interval).

Study Conclusion

• This study suggests that SeM antibody titers can be increased after infection (≥1:12 800) even in the absence of strangles complications.
• Therefore, it proposes that while the presence of SeM antibodies can be indicative of an infection, higher levels of these antibodies could mark the possibility of complications in strangles infections.