Immunization of pregnant sows with a novel virulence gene deleted live Salmonella vaccine and protection of their suckling piglets against salmonellosis.

This study was carried out to examine a novel Salmonella Typhimurium (S. Typhimurium) vaccine for protection of suckling piglets against salmonellosis by immunization of pregnant sows using various administration routes. The vaccine strain was constructed by deletion of cpxR and lon from a wild type S. Typhimurium and the S. Typhimurium Delta cpxR Delta lon Delta asd secreting the B subunit of the Escherichia coli heat-labile enterotoxin were used as a live form of mucosal adjuvant for this study. Pregnant sows were divided into 4 groups of 3 sows a piece. Sows were primed at 8 weeks of pregnancy and were boosted 11 weeks of pregnancy. Group A sows were primed intramuscularly with the formalin-inactivated vaccine and boosted orally with the live vaccine and mucosal adjuvant, group B sows were orally primed with the live vaccine and mucosal adjuvant and boosted orally with live vaccine, group C sows were orally primed with live vaccine and mucosal adjuvant and intramuscularly boosted, and group D sows were primed and boosted with phosphate-buffered saline as controls. Piglets were orally challenged with a virulent S. Typhimurium strain at day 6 after birth. Sows from group A and B had significantly increased IgG levels compared to control group sows (P<0.05), and group C sows had lower IgG levels compared to group A and B sows. Mucosal sIgA and IgG levels in group A and B sow colostrums were significantly increased as compared to those of group D sows (P<0.05). Serum IgG and IgA levels in group A and B piglets were also significantly increased as compared to those of group D piglets (P<0.001). These data suggested that systemic and mucosal immune responses were highly induced by the vaccine candidate, especially when this was administered by both routes of intramuscular-prime and oral booster, and oral prime and booster. Furthermore, clinical signs such as diarrhea and weight loss were not observed after virulent Salmonella strain challenge in group A and B suckling piglets, however, group C (41.7%) and group D (83.3%) piglets suffered from diarrhea. This data suggested that sow immunized by intramuscular-prime and oral booster and oral prime and oral booster with this vaccine candidate effectively protected piglets from salmonellosis.