Use of "E. coli" K99 vaccines in ewes to passively protect lambs against experimental colibacillosis.

Pregnant ewes were vaccinated with partially purified, cell free K99 antigen prepared from the enterotoxigenic E. coli (ETEC) strain (0101:K99:NM) to passively immunize their lambs via the colostrum. After sucking their dams the lambs were infected orally with 10(10) - 10(11) organisms of the heterologous ETEC strain B44 (09:K30:K99), which possesses only the K99 antigen in common, within 4-21 h. of birth. All four control lambs from unvaccinated ewes challenged with E. coli strain B44 developed severe watery diarrhoea whereas none of the 10 lambs from vaccinated dams showed any signs of illness. Vaccination stimulated the production of K99 antibodies which could be detected by an indirect haemagglutination test and haemagglutination inhibition test. Experiments with brush border cells from calf intestine showed that the antibodies were associated with anti-adhesive activity. The antibodies which were predominantly IgG did not neutralize the activity of heat stable enterotoxin and it was concluded that neutralization of the adhesive properties of K99 positive E. coli by colostral antibodies significantly contributed to the resistance of the lambs from vaccinated dams.