In the introduction to this review paper, the mechanisms of pathogenicity of Eschercihia (E.) coli in animals, including particularly pigs, are characterized. The paper provides definitions of enterotoxigenic pathotype (ETEC), the Shiga-toxin-producing pathotype (STEC), the enteropathogenic pathotype (EPEC), and the extraintestinal pathotype (ExPEC), as well as presents the major types (virotypes) of E. coli that cause neonatal diarrhea in piglets and post-weaning diarrhea in pigs. Neonatal infections are prevented by the vaccination of the pregnant sow, which provides the suckling piglets with passive colostral and lactogenic immunity. The main purpose of this paper was therefore to discuss oral subunit vaccines and live oral vaccines against post- -weaning colibacillosis in pigs. The paper cites literature indicating that subunit vaccines containing purified fimbriae, particularly F4, which are important pathogenicity factors in the colonization of the pig’s intestine, given orally to weaned pigs, can protect them against oral challenge with virulent F4+ETEC. The use of alfalfa plants as a delivery vehicle for F4 is suggested. Positive results obtained for vaccines containing F4 have not been repeated in the case of vaccines with F18. Nevertheless, the above-mentioned results for F4 open new possibilities for the development of combined subunit vaccines against the F4+ and F18+ strains of E. coli, which are the major etiological agents of post-weaning diarrhea in pigs. Further in the paper, live oral ETEC vaccines for the prevention of post-weaning colibacillosis in pigs are characterized. They contain fimbrial live attenuated strains or wild strains, which are a priori non pathogenic, as they do not produce enterotoxins. After oral administration, these bacteria adhere to the fimbrial receptors of intestinal epithelial cells, initiating the immune response of the vaccinated pigs against fimbriae and preventing the colonization of the small intestine. The priming of the immune system with levamisole via intramuscular injection before oral vaccination, improves significantly the post-vaccinal immunity. Based on the this technology, a live vaccine against F4+ETEC post-weaning diarrhea, called Coliprotec, was commercialized by Prevtec microbia in Canada in 2008 and also introduced in Brazil in 2011. The introduction of this vaccine in Europe is planned in 2014. Since post-weaning diarrhea caused by F4+ETEC occurs shortly after the weaning of pigs, the vaccination is recommended shortly before weaning. In order to enhance the efficacy of subunit and live vaccines administered orally to pigs, it is recommended to encapsulate them for protection of their immunogenic properties during transport through the gastrointestinal tract. Parenteral vaccination against post-weaning porcine colibacillosis stimulates above all the systemic rather than the mucosal immune system. Its value in protecting the pigs against post-weaning colibacillosis is therefore small or none. Considering the serious losses caused by post-weaning colibacillosis in swine production, further research is needed to improve the efficacy of vaccines against this disease. An effective vaccine could also make it possible to reduce the use of antimicrobials, as called for by the WHO and the OIE.
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