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The efficacy of vaccination against enteric colibacillosis was evaluated in conventionally reared, artificially infected early weaned piglets.
Successful infection with profuse diarrhoea was produced with haemolytic E. coli E145 administered orally to piglets derived from normal sows. Active immunisation of the piglets soon after birth with strain E145 did not protect them from diarrhoea when they were challenged with the same organism. Passive immunisation of piglets with parenterally injected immune serum from a sow vaccinated with strain E145 also failed to protect. On the other hand, no diarrhoea was induced in piglets from sows vaccinated with the challenge organism, although intermittent loose faeces were observed for a relatively short time.
Large numbers of E. coli E145 were excreted 2 days after oral challenge in the faeces of the offspring of normal sows. In contrast, this organism appeared, on the average, 4 days later in the faeces of piglets derived from the vaccinated sows; it was excreted for a shorter time and in smaller numbers.
Circulating antibodies against E. coli E145 were detected by passive cutaneous anaphylaxis before challenge only in piglets derived from vaccinated sows. High serum antibody levels against E145 were detected in all piglets after challenge, irrespective of whether they had actual diarrhoea or not.
A non-haemolytic E. coli strain Mac 111, isolated from a piglet with enteric colibacillosis, failed to induce this disease experimentally.
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