Isolation and serial propagation of human group C rotaviruses in a cell line (CaCo-2)

Rotaviruses were detected via electron microscopy in fecal specimens collected from school children during an outbreak of diarrhea and from a sporadic case in 1993 in Japan. All of the viruses were found to belong to human group C rotavirus by reverse passive hemagglutination assay (RPHA). These viruses replicated well in a human colon carcinoma (CaCo-2) cell line cultured in the presence of trypsin (4 micrograms/ml). This report demonstrates that human group C rotaviruses can be propagated efficiently in a cell line cultured in the presence of trypsin. The infected cells did not show any apparent cytopathic changes. However, virus was detected in the cell cytoplasm by immunofluorescence (IF) staining and in the culture supernatant by RPHA. On the basis of immune electron microscopy (IEM), virus particles collected from infected CaCo-2 cell cultures were confirmed to aggregate specifically with anti-human group C rotavirus antibody. The electrophoretic patterns of RNA segments extracted from viral particles found in the fecal specimens or infected cells were identical to those of human group C rotavirus. These results indicated that human group C rotaviruses were the causal agent of the diarrhea outbreak.