Master of Science / Department of Clinical Science / Elizabeth Davis / Background: 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.

Streptococcus zooepidemicus (Sz) and Streptococcus equi (Se) share 98% DNA sequence homology, but display different pathogenic properties. Infection by one organism does not cross-protect against the other. To better understand pathogenic differences between these organisms and gain information about which proteins are expressed in horses infected experimentally with Se, intrauterine Sz or naturally with respiratory Sz we compared antibody specificities of convalescent sera using ELISA. These comparisons were based on sets of 8 and 14 immunoreactive recombinant proteins of Se strain CF32 and Sz strain NC78, respectively. Sera from donkeys that were previously naturally affected with strangles and later developed Sz pneumonia secondary to an experimental influenza challenge were also included. Serum antibody responses were quantitatively and qualitatively much greater following recovery from strangles than following respiratory Sz infection. Increased reactions to Se proteins IdeE2, Se75.3, Se46.8, Se18.9 and Se42.0 were observed for the majority of strangles sera but not for sera from respiratory Sz infection cases. Reactions of sera from Sz respiratory disease to Sz proteins varied greatly and were mostly to HylC and ScpC. Interestingly, sera of donkey recovered from Sz bronchopneumonia did not show increased antibody reaction to any of the proteins even though these donkeys had also recovered from clinical strangles 6 months previously. Only 1/5 mare with Sz placentitis presented increased serum antibody responses to MAP. In conclusion, adaptive immune responses to Se of horses with strangles are stronger and involve a greater number of proteins than adaptive immune responses to Sz infection of the lower respiratory tract. In an effort to develop an improved vaccine against Se, modified live strain of EHV-1, RacH was constructed to express three recombinant antigens of Se SeM, IdeE and Se18.9. Two groups of 10 and 2 ponies were vaccinated intramuscularly or intranasally, respectively. Another group (n=6) vaccinated with empty RacH served as controls. Sera from 2/3 ponies from each vaccination groups and 1/2 serum from IN vaccinated ponies showed increased serum neutralizing antibodies to EHV-1. ELISA detected no significant increase in antibodies to proteins. Only one IM and IN vaccinated pony showed serum bactericidal activity post vaccination.