Colibacillosis in swine

Escherichia coli (E. coli) are an important cause of disease in new-born and recently weaned piglets. In new-born piglets, severe watery diarrhoea can be caused by enterotoxigenic E. coli (ETEC) producing F4 (K88), F5 (K99), F41 and or F6 (P987) fimbriae. Colibacillosis in weaned piglets is the result of infection with F4+ or F18+ ETEC or F18+ verotoxigenic E. coli (VTEC). Besides fimbriae, ETEC produce thermolabile (LT), thermostable a (STa) and/or b (STb) enterotoxins which induce the secretory diarrhoea resulting in weight loss, growth retardation and mortality, whereas VTEC produce the Shiga toxin Stx2e that binds to globotetraosylceramide on endothelial cells, resulting in oedema, haemorrhage and microthrombosis leading to nervous signs and mortality. New-born animals can be protected via the milk against neonatal colibacillosis by vaccination of the sows. This lactogenic immunity ceases at weaning making weaned piglets highly susceptible again for enteropathogens. Weaned piglets lack or weakly express receptors for F5, F6 and F41 fimbriae, this is not the case for F4 fimbriae. The latter are highly expressed in the jejunum of newly weaned piglets making them highly susceptible to F4+ ETEC infections. Three serological variants of F4 have been identified namely F4ab, F4ac and F4ad. Piglets can have receptors on their enterocytes for adhesion of one or more of these F4 variants, but receptor expression can also be completely absent, resulting in resistance against infection. We have demonstrated that F4ac is a highly immunogenic fimbriae that upon oral administration, results in a F4-specific intestinal IgA response and a protective mucosal immunity against an infection with a virulent F4ac+ ETEC strain. Of F18 also two serological variants have been identified, namely F18ab and F18ac. In contrast to the F4 serological variants, both F18 variants have the same adhesion, FedF and binds to the same receptors on the villous enterocytes. We recently identified these receptors as blood group O/A sugars.

Receptors for F18 fimbriae are absent in new-born piglets and gradually appear at the age of 1 week, resulting in sufficient receptors in 3-week-old piglets for colonization with the F18+ ETEC and/or VTEC strains. F18 fimbriae are not very immunogenic. Oral administration does not result in an immune response. Prevention of post-weaning colibacillosis is difficult and should be based on prevention of predisposing factors, high hygiene and stimulation of the immune system. Although oral vaccines are on the market in the US and Canada, there is doubt on their efficacy and there is need for developing vaccines which can be applied during the suckling period.