This study, the first survey of CHRVs in various locations in Japan, indicated that CHRVs are widely distributed in Japan. The rates of CHRV positivity ranged from 2.7 to 13.3%, and the CHRV isolates were mainly detected in March and April. Moreover, CHRVs principally prevailed in children ages 3 to 8 years. These epidemiological features are clearly distinct from those of the human group A rotavirus. Oseto (16
) previously carried out an epidemiological study of CHRVs over a 3-year period in Matsuyama City, Japan. Our observations were consistent with those reported by Oseto (16
In this study, we screened only the human group A rotavirus-negative specimens for the presence of CHRV. Jiang et al. (9
) have recently reported mixed infections with human group A and group C rotaviruses in the United States. We therefore examined by the RPHA test group A rotavirus-positive specimens (n
= 52) that were collected in Okayama and Shimane (data not shown), but none of the specimens was positive for CHRV, indicating that the mixed infection might be rather rare. In fact, Jiang et al. (9
) recognized only one mixed infection among 1,676 samples. However, screening of rotavirus infections must hereafter include screening for mixed infection.
The RPHA test could successfully detect CHRVs even in fecal specimens that were insufficient for immune electron microscopy or genome electropherotype analyses. To inspect the specificity of the RPHA test, the RPHA test-positive specimens were examined by our ELISA system (6
), and all were determined to be positive. Recently, the PCR method has been applied to the detection of group C rotaviruses by Gouvea et al. (8
). Although the sensitivity of the RPHA test is not comparable to that of the PCR method, the former test is faster and simpler and is more suitable for use for routine diagnosis in clinical settings.
In group A rotaviruses, genome electropherotyping of field isolates is a useful tool for obtaining epidemiological information about the origin of the isolates and diversity among these isolates, because each isolate reveals a unique genome profile (1
). The genome electropherotypes of the isolates retrieved in 1993 were surprisingly similar to each other, regardless of the prefectures from which the isolates were obtained. Moreover, the dot blot hybridization analysis showed that the VP7 genes of the isolates were highly homologous. These results strongly suggest that a large-scale outbreak of CHRV occurred during the winter of 1992 and 1993 in Japan. However, further comparative analysis of other genome segments will be required to confirm this hypothesis.
The electropherotype of the K9304 strain, which represented isolates retrieved in 1993, was compared with those of the pattern I and II strains in the same gel. Although K9304 revealed a distinct genome profile tentatively designated pattern III, this electropherotype seemed to be a combination of patterns I and II. The sequence analysis of the VP7 gene from K9304 also showed that the VP7 gene of K9304 was similar to that of the pattern I strain. These results indicate that the K9304 strain may be a reassortant virus between the pattern I and pattern II strains, because it has been reported that natural reassortants occurred between human group A rotaviruses strains belonging to different genogroups (13
). Quite recently, CHRVs have been successfully propagated in a continuous cell line (CaCo-2) (15
). To clarify the genetic and antigenic relationship among three strains with distinct electropherotypes, we are now attempting to adapt these strains to CaCo-2 cells.