Protection of pigs against experimental Salmonella Typhimurium infection by use of a single dose subunit slow delivery vaccine

Infections caused by septicemic strains of Salmonella are significant animal health as well as food safety concerns for the North American swine industry. Among the various strategies to control these infections at the herd level, development of vaccines are attractive alternatives. In this study, based on previous studies of immune response to various protems following natural and experimental infections of pigs by Salmonella, we designed a subunit slow delivery vaccine and tested it in an experimental model of infection. The selected immunogenic protein was cloned and purified by chromatography. The purified protein was then incorporated m PLGA (a polymer that is slowly degraded within the animal\u27s gastro-intestinal system) microspheres and given orally once to groups of pigs (n=8) while control animals (n=8) received only PBS. Animals were challenged orally 4 weeks after the vaccmation with 108 cells of a virulent strains of Salmonella Typhimurium. Animals were examined twice a day and climcal signs evaluated using a predetermined scoring grid. Pigs were sacrificed 12 days later and bacterial cultures of vanous organs, electron microscopy and evaluation of lgA response by ELISA were performed. No significant difference was found at bacteriology and ELISA but marked differences in clinical signs were observed between vaccinated and non vaccinated animals. None of vaccmated animals showed fever exceeding 40°C while it was observed in 5 out of 8 non vaccinated Only one of vaccmated pigs showed mild diarrhea while severe diarrhea was observed in all control animals different sizes of microspheres were observed in intestinal crypts of vaccinated animals at electron microscopy. We concluded that this vaccine can protect pigs against clinical signs associated with experimental infection by Salmonella Typhimunum