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An Optimized Hemagglutination Inhibition HI Assay to Quantify Influenza-specific Antibody Titers
Published on: December 1, 2017
Strangles, convalescent Streptococcus equi subspecies equi M antibody titers, and presence of complications
Katherine M Delph1, Laurie A Beard1, Amanda C Trimble1
1Department of Clinical Sciences, Kansas State University, College of Veterinary Medicine, Manhattan, Kansas.
Background:
Streptococcus equi subspecies equi infection elicits M protein antibody titers in equids. Interpretation of titers is not generally accepted.
Hypothesis:
The magnitude of S. equi M protein (SeM) antibody titer after infection (titer ≥1:12 800) will be useful to monitor for the presence of complications or the risk of development of complications.
Animals:
Forty-eight horses on 1 farm involved in strangles outbreak.
Methods:
Clinical and observational study. S. equi M protein antibody titers were measured on all horses 8 weeks after infection and select horses 12 and 28 weeks after infection. Horses were categorized: no disease, uncomplicated case, persistent guttural pouch (GP) infection, or complicated cases (metastatic abscesses, purpura hemorrhagica, secondary infections, and dysphagia). Category was compared to titer.
Results:
Twenty-eight of 48 (58%) developed clinical signs of S. equi infection. Of those, 11 (39%) had uncomplicated strangles, 9 (21%) had persistent GP infection, 5 (18%) were complicated cases, and 3 (11%) had both persistent GP infection and complications. Thirty-three percent of horses (16 of 48) had SeM antibody titers ≥1:12 800 eight weeks after infection. Of horses with titers ≥1:12 800, 6 of 16 had evidence of complications. Of complicated cases, 6 of 8 had titers ≥1:12 800. In this outbreak, the sensitivity (75%; 95% CI [confidence interval] 45-105) for a SeM antibody titer ≥1:12 800 detecting complications was higher than the specificity (43%; 95% CI 23-64).
Conclusions And Clinical Importance:
This outbreak demonstrates that SeM antibody titers can be increased after infection (≥1:12 800) in the absence of complications of strangles.
Insights
High Streptococcus equi M protein (SeM) antibody titers in horses after infection may indicate complications. However, elevated SeM titers alone do not always signify strangles complications, as seen in this outbreak study.
Area of Science:
- Veterinary Immunology
- Equine Infectious Diseases
- Bacteriology
Background:
- Streptococcus equi subspecies equi causes strangles in horses, eliciting M protein antibody titers.
- Interpretation of these titers for disease monitoring is not universally accepted.
Purpose of the Study:
- To evaluate the utility of Streptococcus equi M protein (SeM) antibody titers (≥1:12,800) in monitoring for strangles complications in equids.
- To determine if high SeM titers correlate with the presence or risk of developing complications.
Main Methods:
- A clinical and observational study was conducted on 48 horses following a strangles outbreak.
- SeM antibody titers were measured 8, 12, and 28 weeks post-infection.
- Horses were categorized by disease outcome: uncomplicated, persistent guttural pouch infection, or complicated cases.
Main Results:
- 58% of horses developed clinical signs; 39% had uncomplicated strangles, 21% had persistent guttural pouch infection, and 18% had complications.
- 33% of horses achieved SeM titers ≥1:12,800 eight weeks post-infection.
- Of horses with titers ≥1:12,800, 6/16 had complications, and 6/8 complicated cases had titers ≥1:12,800. Sensitivity for detecting complications was 75%, specificity 43%.
Conclusions:
- Elevated SeM antibody titers (≥1:12,800) can occur after S. equi infection even without strangles complications.
- While high titers show some correlation with complications, they are not definitive indicators on their own.
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