Active oral immunization of suckling piglets to prevent colonization afterweaning by enterotoxigenic Escherichia coli with fimbriae F18

Immunoprophylaxis of porcine oedema disease and post-weaning diarrhoea caus ed by strains of Escherichia coli expressing fimbriae F18 is an unsolved pr oblem. The study was designed to examine whether vaccination with a live F1 8ac vaccine of unweaned pips born to sows with F18ac antibody in the colost rum requires preformed fimbriae in the vaccine, and whether protection agai nst the heterologous fimbrial variant F18ab is induced as well. Genetically susceptible pigs were vaccinated orally on three consecutive days, beginni ng 10 days before weaning with 10(11)CFU of an F18ac culture. Challenge wit h a dose of 10(7)CRT of E. coli F18 on three consecutive days was initiated 9 or 11 days after weaning. Eighteen pigs given the fimbriated F18ac vacci ne and challenged with a strain of the homologous fimbrial variant were pro tected against colonization; mean faecal viable counts of the challenge str ain were >3 log(10) lower than those from the 17 nonvaccinated control pigs . The vaccinated pigs developed a significant rise of F18ac IgA serum antib odies. The 23 pigs which had received the non-fimbriated vaccine showed no significant protection and exhibited much lower serum F18ac IgA ELISA react ivities. Eighteen pigs vaccinated with the fimbriated F18ac and challenged with an F18ab strain had faecal viable counts nearly as high as those from 16 non-vaccinated control pigs. It is concluded that only oral vaccines hav ing preformed fimbriae induce protection limited to the homologous fimbrial variant. (C) 2000 Elsevier Science B.V. All rights reserved.