Norwalk virus (NV) and Sapporo virus (SV) were approved as type species of the genus Norwalk-like viruses and the genus Sapporo-like viruses, respectively, within the family Caliciviridae. To clarify the importance of NV and SV as causes of gastroenteritis outbreaks in infants, stool samples obtained from 36 outbreaks of nonbacterial gastroenteritis that occurred during 1976-1995 in an infant home in Sapporo, Japan, were examined for diarrhea viruses using electron microscopy, enzyme immunoassays, reverse transcriptase-polymerase chain reaction (PCR), and sequencing of the PCR products. NV and SV were associated with 15 (42%) of the 36 outbreaks and were more prevalent than rotavirus (RV) A, which was associated with 10 (28%) of the 36 outbreaks. Our data indicate that NV and SV were the most common cause of outbreaks of viral gastroenteritis in infants and were indeed more prevalent than RV-A in Sapporo, Japan, during 1976-1995.

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An epidemiological study on the G serotype distribution of group A rotaviruses (GARV) isolated in Kenya was carried out in one urban hospital in Nairobi and in two rural hospitals in Nanyuki and Kitui to clarify the prevalent G serotypes before future introduction of the ready licensed rotavirus vaccine in Kenya. A total of 1,431 stool specimens were collected from children, who were mainly outpatients, aged from 0 to 6 years old with acute gastroenteritis from August 1991 to July 1994. Samples positive for GARV by conventional ELISA were then analyzed by subgrouping and serotyping ELISA and by PAGE. To ascertain the G serotypes of viruses in samples that were unable to be typed by serotyping ELISA, polymerase chain reaction was also attempted. The prevalence of GARV was 28.4% in the urban hospital, 22.5% in Nanyuki, and 13.7% in Kitui. Among rotavirus-positive samples, subgroup II rotaviruses were detected in 63.1%, and subgroup I rotaviruses were 25.9%. Serotype G4 was most prevalent, accounting for 41.6% followed by 23.3% of serotype G1, 17.0% of serotype G2, and serotype G3 was rarely isolated. Seven strains of serotype G8/P1B rotavirus was detected for the first time in Kenya by RT-PCR. Eleven specimens with an unusual composition of subgroup, serotype, and electropherotype were atypical GARV in which the P-serotype was P1A, P1B, or P2. Although uncommon GARV serotype G8/P1B and atypical GARV were detected, the four major GARV serotypes, G1 through G4, should be targeted at this moment for vaccination to control this diarrheal disease in Kenya. Continuous monitoring of the G- and P-serotype distribution of GARV should provide important information about the impact of rotavirus vaccination in Kenya.

Group A rotavirus (GAR) G8P[1] strains, found sometimes in cattle, have been reported rarely from humans. Therefore, analysis of the full genomes of human G8P[1] strains are of significance in the context of studies on interspecies transmission of rotaviruses. However, to date, only partial-length nucleotide sequences are available for the 11 genes of a single human G8P[1] strain, while the partial sequences of two other strains have been reported. The present study reports the first complete genome sequence of a human G8P[1] strain, B12, detected from an asymptomatic infant in Kenya in 1987. By nucleotide sequence identities and phylogenetic analyses, the full-length nucleotide sequences of VP7-VP4-VP6-VP1-VP2-VP3-NSP1-NSP2-NSP3-NSP4-NSP5 genes of strain B12 were assigned to G8-P[1]-I2-R2-C2-M2-A3-N2-T6-E2-H3 genotypes, respectively. Each of the 11 genes of strain B12 appeared to be more related to cognate genes of artiodactyl (ruminant and/or camelid) and/or artiodactyl-derived human GAR strains than those of most other rotaviruses. Strain B12 exhibited low levels of genetic relatedness to canonical human GAR strains, such as Wa and DS-1, ruling out the possibility of its origin from reassortment events between artiodactyl-like human and true human strains. These observations suggest that strain B12 might have been directly transmitted from artiodactyls to humans. Unhygienic conditions and close proximity of humans to livestock at the sampling site might have facilitated this rare event. This is the first report on a full genomic analysis of a rotavirus strain from Kenya. To our knowledge, strain B12 might be the oldest G8 strain characterized molecularly from the Africa continent.

We report here the full genomic analysis of a simian SA11-like G3P[2] group A rotavirus (GAR) strain, B10, isolated from an asymptomatic infant in Kenya in 1987. By nucleotide sequence identities and phylogenetic analyses, the VP7-VP4-VP2-VP3-NSP1-NSP2-NSP3-NSP5 genes of strain B10 exhibited maximum genetic relatedness to those of the different isolates of simian strain SA11, and were assigned to the G3-P[2]-C5-M5-A5-N5-T5-H5 genotypes, respectively. On the other hand, the VP1, VP6 and NSP4 genes of strain B10 did not belong to any of the established GAR genotypes, and therefore, were assigned to new genotype numbers R8, I16 and E13, respectively, by the Rotavirus Classification Working Group. These observations suggested that strain B10 might have originated from reassortment event/s involving simian SA11-like strains and GAR strains from unknown animal host species (possibly other wild animals) preceding transmission to humans. Alternatively, considering the lack of data on simian GARs, it might be also possible that the VP1, VP6 and NSP4 genes of strain B10 are those of unknown simian strains, and that strain B10 might be a typical simian strain that was directly transmitted to humans. Therefore, either hypothesis pointed towards a rare instance of possible direct transmission of GARs from an animal host (possibly a monkey or some other wild animal) to humans. This was corroborated by the presence of different species of wild animals including non-human primates, and unhygienic conditions at the sampling site. To our knowledge, the present study is the first report on the detection of a simian SA11-like G3P[2] GAR strain in humans.