Immunisation of the equine uterus against Streptococcus equi subspecies zooepidemicus using an intranasal attenuated Salmonella vector

Attenuated Salmonella enterica serovar Typhimurium MGN707, expressing the SzP protective protein of the MB9 serovar of Streptococcus equi subspecies zooepidemicus (SzP-MB9) was tested for its safety and efficacy as a nebulised intranasal vaccine against streptococcal uterine infections in mares. In a preliminary study, vaccinated mares (n = 5) displayed serum, nasal and uterine responses (P < 0.05) to S. Typhimurium lipopolysaccharide (St-LPS). Subsequently, vaccinated mares (expressor group, n = 7), but not mares vaccinated with the vector only (control group, n = 7), displayed significant increases in SzP-MB9 antibodies in serum, nasal and uterine washes (P < 0.05). Assuming the uteri of all nine mares were free of streptococci prior to challenge with 6.3 × 109 colony forming units of S. e. zooepidemicus MB9, significantly fewer S. e. zooepidemicus were cultured from the uterine flushings of expressor-vaccinated mares (n = 4) compared to control-vaccinated mares (n = 5) (P < 0.001). The only adverse reaction to vaccination was nasal haemorrhage in one mare.