Progress and Challenges in Vaccine development Against Enterotoxigenic Escherichia Coli (ETEC)-Associated porcine Post-Weaning Diarrhoea (PWD)

Porcine Post-Weaning Diarrhea (PWD) continues to be one of the most important swine diseases worldwide. Entero toxigenic Escherichia coli (ETEC) strains are the primary cause of PWD. The key virulence factors of ETEC in PWD are bacterial fimbrial adhesins and enterotoxins. Adhesions mediate ETEC bacteria initial attachment to pig epithelial cells and subsequent colonization at pig small intestines. Enterotoxins including heat-labile toxin (LT) and heat-stable toxin (ST) disrupt fluid homeostasis in small intestinal epithelial cells to cause electrolyte-rich fluid hyper-secretion and diarrhea. Currently there are no effective prevention measures to protect weaned pigs against PWD. Vaccination would be the most practical and effective prevention approach, and vaccines inducing anti-adhesion immunity to block ETEC attachment and colonization and also antitoxin immunity to neutralize enterotoxicity are considered optimal against ETEC-associated PWD. Although progress has been made in past decades in developing effective vaccines against PWD, challenges continue to exist due to the disease complexity and immunological heterogeneity among ETEC strains. Recent progress in using safe toxoid antigens, toxoid fusion antigens and MEFA (multiepitope fusion antigen) approach to develop multivalent vaccines for broad protection, however, shows promising in developing new vaccines for effective protection against ETEC-associated PWD.