Concurrent experimentally induced infection with Eimeria bovis and coronavirus in unweaned dairy calves
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Summary
Over a period of 3 summers, 21 colostrum-fed Holstein bull calves, 1 to 3 days old, were assigned to 7 replicates, each consisting of 3 calves. Within each replicate of 3 calves, 2 were selected at random, to be given 100,000 to 146,000 sporulated coccidia oocysts (principally Eimeria bovis) orally 60 hours after arrival at the college research farm. On the thirteenth day after coccidia inoculation, 1 of the 2 calves that had been given coccidia and the third calf that had not been inoculated, were given coronavirus by intranasal and oral routes. Calves were observed daily, and consistency of feces was scored visually. Nasal swab specimens for indirect immunofluorescent antibody testing for coronavirus and fecal samples for oocyst determination were obtained approximately every third day. Of 7 calves that were given only coronavirus, 3 developed diarrhea of short duration. Of 7 calves that were given only coccidia oocysts, 6 developed diarrhea. All 7 calves inoculated initially with coccidia and subsequently with coronavirus developed diarrhea. For 5 of 7 replicates, calves that were given coccidia and coronavirus developed diarrhea first. When overall severity, measured by fecal score and by blood in the feces, was compared, calves inoculated with coccidia followed by coronavirus were more severely affected (P < 0.05) than were calves that were given only coronavirus. Calves that were given only coccidia oocysts appeared more severely affected than calves that were given only coronavirus, but differences were not significant. Calves that were given either coccidia alone, or coccidia followed by coronavirus, had more severe lesions of mucosal degeneration/epithelial necrosis and inflammation (P < 0.05) than did calves that were given only coronavirus. Lesions, however, were generally most severe in calves that were given coccidia and coronavirus. In 4 calves, fibrinopurulent typhlitis and/or colitis were observed; 3 of these observations were made in calves that were given coccidia followed by coronavirus. These observations indicate that, although coronavirus infection in young calves is common and may be mild in calves given adequate colostrum, when combined with coccidia (principally E bovis) infection, resultant clinical signs of disease and lesions may be more severe than those associated with infection attributable to either coronavirus or coccidia alone.
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