Intranasal Vaccination to Boost Equine Immunity to Uterine Streptococcal Infection

Standardbred mares were immunized intranasally using a Salmonella typhimurium vector expressing the Streptococcus zooepidemicus protein MB9 (SzP-MB9) to determine the serum, nasal, and uterine mucosal antibody response. The experiment was performed in three separate stages, each a distinct experiment in itself. Phase I was performed in 2001, and was a comparison of five mares vaccinated with the SzP-MB9-expressing vaccine vs. five nonvacci-nated mares. Antibodies were analyzed via enzyme-linked immunosorbent assay (ELISA). IgA and IgG levels against both Salmonella-LPS (St-LPS) and SzP-MB9 were analysed in serum, nasal and uterine washes collected before and after vaccination. Phase II was performed in 2003 and was a comparison of seven mares vaccinated with the SzP-MB9-expressing vaccine (expressor vaccinated) vs. seven mares vaccinated with a control vector strain (control vaccinated) that was identical to the vaccine except that it lacked SzP-MB9 expression. Analysis of IgA and IgG levels in serum, nasal and uterine washes collected before and after vaccination was performed using ELISA. Phase III was performed in 2006 and compared five expressor vaccinated mares to five control vaccinated mares (the same as in Phase II). The mares were intrauterinely inoculated with a Streptococcus zooepi-demicus serovar MB9 culture after vaccination, and blood agar plates were streaked from uterine washes taken 24, 48 and 120 hours after inoculation. Quantitative colony forming unit (CFU) counts were used to analyze the rate of clearance of the introduced bacteria to determine if the vaccine was protective in practice. Analyses showed increases in St-LPS-specific IgG and IgA levels nasal and uterine washes as well as serum after vaccination in the expressor vaccinated mares in Phase I, and an increase in SzP-MB9-specific nasal IgA. Phase II showed a significant increase in St-LPS-specific IgA and IgG in the serum and of IgA in nasal and uterine washes of all the mares (expressor vaccinated and control vaccinated). Significant Increases of SzP-MB9-specific IgA and IgG in the serum and IgA in nasal and uterine washes were detected for expressor vaccinated mares, but not for control vaccinated mares, which indicated the vaccine was successful in eliciting a mucosal antibody response after nasal vaccination. The Phase III challenge, however, was inconclusive. Colony-forming unit (CFU) counts and uterine fluid levels decreased more rapidly in the expressor vaccinated group than in the control vaccinated group, but the difference was statistically insignificant. Sufficient evidence was, however, gained to suggest the vaccine may be protective, which warrants further research. No adverse reactions to the vaccine were detected in any of the mares, indicating its safety