Twenty 6-to 7-hour-old gnotobiotic calves inoculated orally with attenuated calf diarrhea reovirus-like agent and challenge-inoculated with virulent virus 48-72 h post-inoculation (PI) remained clinically normal during the post-vaccination observation period; one developed mild diarrhea after challenge inoculation. Four non-vaccinated challenge control calves developed severe diarrhea. Twenty 6-to 7-hour-old gnotobiotic calves inoculated orally with attenuated calf diarrhea coronavirus and challenge inoculated with virulent virus 96 h later remained clinically normal during the post-vaccination and post-challenge observation period. Four non-vaccinated challenge control calves developed severe diarrhea and 2 of these died. Five-foot long isolated loops prepared in the lower ileum (Thiry-Vella loop) of newborn colostrum-deprived calves were inoculated with attenuated coronavirus. Daily loop washings were cultured for virus and tested for neutralizing antibody. Peak viral titers of 10(6.5) to 10(7) occurred 3-4 days PI and descended rapidly to 0 between 6 and 8 days PI. Neutralizing antibody was first detected in the washings 6-8 days PI and reached a titer of 128-256 7 to 9 days PI. Loop immunoglobulin separated by gel filtration and identified by immunodiffusion were primarily IgM and IgA. Initial resistance to virulent viral infection is thought to be due to an interference phenomenon, with later resistance due to local antibody.
Immune response to orally administered calf reovirus-like agent and coronavirus vaccine.