Pathology of Neonatal Calf Diarrhea Induced by a Coronavirus-Like Agent

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Abstract
Lesions induced by a bovine coronavirus-like agent were studied in gnotobiotic and colostrum-fed calves using gross, histologic and electron microscopic procedures. Lesions in gnotobiotic calves were present in the colon, mesenteric lymph nodes and in all segments of the small intestine. Calves killed 4 h after the onset of diarrhea had immunofluorescent epithelial cells on the villi of the small intestine and surface of the colon. Calves killed at 44 h had shortened intestinal villi and cuboidal epithelial cells. The villus-to-crypt ratio in the lower small intestine averaged 1.0 compared with 5.3 in a control calf. Immunofluorescent cells were present at the tips of the villi, and at the surface and in the crypts of the colon. Colostrum-fed calves that had serum-neutralizing antibody titers for the coronavirus-like agent developed diarrhea when inoculated orally with the agent. There was good correlation between histologic, immunofluorescent and electron microscopic findings.