Comparison of immunologic responses following intranasal and oral administration of a USDA-approved, live-attenuated Streptococcus equi vaccine

Master of ScienceDepartment of Clinical ScienceElizabeth DavisBackground: While there is a commercially-available vaccine for Streptococcus equi subsp. equi licensed for the intranasal route of administration, some equine practitioners are administering this vaccine orally despite a lack of evidence for its efficacy by this route of administration. Objectives: To compare systemic and local immune responses following intranasal or oral administration of the USDA-approved, live-attenuated Streptococcus equi subspecies equi vaccine (Pinnacle IN®, Zoetis, Florham Park, New Jersey). Study Design: Experimental, randomized clinical trial Methods: Eight healthy horses with low Streptococcus equi M protein (SeM) titers (<1:1600) were randomly assigned to an intranasal or oral two-vaccine series. SeM-specific serum immunoglobulins G (IgG) and A (IgA) and nasal secretion IgA were assessed using a commercially-available ELISA (Equine Diagnostic Solutions, LLC, Lexington, Kentucky) and a novel magnetic microsphere assay utilizing fluorescence. A general linear mixed models approach was used for statistical data analysis. Results: As expected, intranasal vaccinates showed substantial increases in both serum SeM-specific IgG and IgA levels post-vaccination (P=0.0006 and P=0.007, respectively). Oral vaccinates showed an increase in serum SeM-specific IgG post-vaccination (P=0.0150), though only one-third the magnitude of intranasal vaccinates. Oral vaccinates showed no evidence of change in SeM-specific IgA post-vaccination (P=0.15). Main Limitations: Changes in mucosal antibody responses were not identified in this study which may be related to small change in antibody response, timing of sample collection, or method of nasal secretion collection. Conclusions: Results indicate that intranasal or oral vaccine administration resulted in increased serum SeM-specific IgG, though the magnitude of response differed between routes

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

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