Gross, immunofluorescent, and light microscopic findings in seven gnotobiotic calves inoculated orally with a Reo-like neonatal calf diarrhea virus were compared to findings in three control gnotobiotic calves. Neonatal calf diarrhea virus infected primarily the villous epithelium of the small intestine. Calves examined within 1.5 h after onset of diarrhea had tall columnar immunofluorescent villous epithelial cells in the middle and lower small intestine. Calves examined 2–4.5 h after onset of diarrhea had cuboidal to squamous villous epithelial cells and an increase in reticulum-like cells in the villous lamina propria of the middle and lower small intestine. Viral tilers were 106 and 108 in colonic contents from two calves inoculated with cell-culture-adapted virus and necropsied, respectively, 2 and 6 h after onset of diarrhea.

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 villusto-crypt ratio in the lower small intestine averaged 1 .O 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 iindings.Diarrhea occurred in calves 5-21 days old on several ranches during a 1971 field trial of an oral neonatal calf-diarrhea vaccine prepared from a reovirus-like agent [9]. Fecal smears from diarrheic calves were immunofluorescent negative for this agent. Diarrheic fecal material from one of the problem herds inoculated into the duodenum of a hysterotomy-derived colostrum-deprived calf caused diarrhea. Feces from this calf contained coronavirus-like particles. Subsequently diarrhea was produced in eight additional calves [9, 111 with fecal material from a calf with experimentally induced diarrhea. Pathological changes in calves inoculated with the coronavirus-like agent are described.

Abstract. Neonatal calf diarrhea induced by a reovirus-like agent was studied by electron microscopy. Gnotobiotic calves were inoculated with virulent and cell-cultureadapted isolates of viruses, and similar results were obtained with both isolates. The virus infected mature villous epithelial cells of the small intestine and replicated predominantly within cisternae of the endoplasmic reticulum. Macrophages within small intestinal villi also contained viral particles. Shedding of virus into the feces apparently resulted from desquaniation of infected epithelial cells. Replacement epithelium did not contain the reovirus-like agent, was of cuboidal or squamous type, and ultrastructurally resembled immature epithelium normally found in the crypts. Escherichia coli was nonpathogenic when inoculated alone and did not adhere to the epithelium when inoculated with the virus. The reovirus-like agent was a primary pathogen since it caused diarrhea and lesions when inoculated alone or with E. coli.Diarrhea of neonatal calves has been a serious and persistent problem of the dairy industry for many years. This disease has become a major problem on ranches with cow-calf operations. Apparently an increased frequency of neonatal calf diarrhea in beef-type calves has been caused by calving during a relatively short period of time in the late winter and early spring when inclement weather causes stress. Cows and their offspring have been concentrated into small areas during the calving season, and transmission of infectious diseases to susceptible calves has been favored.A virus designated initially as neonatal calf diarrhea virus was isolated in 1968 and reported as an etiologic agent in field cases of neonatal calf diarrhea [9]. The disease was reproduced experimentally in specific pathogen-free and gnotobiotic calves inoculated with bacteria-free filtrates obtained from infected calves. Fecal material purified by ultracentrifugation and examined by

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Gnotobiotic newborn calves were found to be susceptible to infection with the reovirus-like agent of human infantile gastroenteritis (HRVL). Infection was based on (i) seroresponse using immunofluorescence and (ii) fecal shedding of virus particles using electron microscopy. Virus was detected in fecal samples for at least 2 to as long as 7 days after inoculation, although peak virus concentrations were observed on days 1 to 4. Diarrheal illness was observed in seven calves on second to fourth serial passage of HRVL in calves but in none of four animals studied on first passage. Diarrhea began 15 to 30.5 h (mean = 22.3 h) post-inoculation and lasted less than 24 h; three of the seven animals that developed diarrhea were also depressed or anorectic.