Protection against neonatal Escherichia coli diarrhea by vaccination of sows with a novel multivalent vaccine candidate expressing E. coli adhesins associated with neonatal pig colibacillosis

In this study, we investigated the optimal condition of a novel multivalent Escherichia coli vaccine candidate for protection efficacy against E. coli colibacillosis in piglets via booster strategy using oral and intramuscular administration routes. The candidate was constructed using an expression and secretion plasmid and an attenuated Salmonella delivery system as described earlier. Pregnant sows were divided into four groups of three sows each and immunized with a mixture of the individual vaccine strains. Sows were primed and boosted at 8 and 11 weeks of pregnancy. Group A sows were primed intramuscularly and boosted orally. Group B sows were primed and boosted orally. Group C sows were orally primed and intramuscularly boosted. Group D sows were primed and boosted with PBS as a control. The serum IgG and IgA levels to individual adhesin antigens were elevated in immunized sows compared to controls, as were colostral IgA and IgG levels of all immunized sows. In addition, serum IgG and IgA levels in piglets from all immunized sows were significantly increased. These data suggest that systemic and colostral immune responses were highly induced by vaccination with the candidate. After challenge with a virulent strain of E. coli, clinical signs such as diarrhea and mortality were not observed in suckling piglets from the immunized sows, while diarrhea and mortality affected 100% and 25% of the control group piglets, respectively. These findings indicate that immunization of sows with the candidate vaccine irrespective of administration routes can effectively protect their piglets against neonatal E. coli diarrhea.