Physicochemical and Biological Properties of Neonatal Calf Diarrhea Coronaviruses Isolated in Quebec and Comparison with the Nebraska Calf Coronavirus

SUMMARY Four coronavirus-like agents (BCQ 1, 2, 3, and 4) isolated from feces of diarrheal calves in Quebec dairy and beef herds and adapted to Vero and Madin-Darby bovine kidney (mdbk) cell cultures were characterized as coronaviruses. Their physicochemical and biological properties were compared with those of the Nebraska calf diarrhea coronavirus (ncdc) adapted to the same permissive cell cultures. Isopycnic gradient ultracentrifugation of the viral material produced in Vero cells with ncdc or BCQ 1, 2, 3, and 4 viruses resulted in three different infective particles with buoyant densities of 1.15, 1.18 to 1.21, and 1.23 g/ml in sucrose. For all isolates studied, infectivity was maximal at the density 1.18 to 1.21 g/ml, and the particles in this peak were generally circular, had a mean diameter of 100 nm, and were covered with petal-shaped projections 10 to 15 nm long. Incompleted particles were observed at the densities 1.15 and 1.23 g/ml. Studies on the filterability of the viruses supported the finding that bovine coronaviruses have a mean diameter of 100 nm. As with ncdc, the growth of the Quebec coronaviruses was not inhibited by inhibitors of DNA metabolism and all viruses were sensitive to lipid solvents and heat treatment, especially at temperatures higher than 45 C. The Quebec bovine coronavirus isolates except BCQ 3 were stabilized at 50 C in presence of 1 M MgCl2 and were stable at pH 3.0. The sensitivity of bovine coronaviruses to trypsin was shown to differ greatly from one isolate to the other. Studies on the pathogenicity of ncdc and one Quebec virus demonstrated that bovine coronaviruses are not virulent for neonatal mice, hamsters, and guinea pigs; nor did these viruses grow in embryonating chicken eggs. All Quebec isolates were shown to agglutinate the same erythrocyte species as the ncdc (rats, mice, hamsters, and guinea pigs), and the hemagglutination was not dependent on the temperature of incubation (4, 25, and 37 C).