The prevalence and genetic diversity of human caliciviruses causing sporadic cases of acute gastroenteritis in young children hospitalized in a large pediatric hospital in Melbourne, Australia over 5 years (incorporating January 1998-December 2002) was studied by reverse transcription and sequence analysis of part of the polymerase gene. The overall prevalence of calicivirus infection in children aged <5 years during the 5 year study was 9.2% (113/1,233), with 95% of the strains belonging to the Norovirus genera. Strains of the norovirus G11-4 cluster were the most common type identified in 4 of the 5 years studied (1998, 1999, 2001, and 2002), with strains of norovirus cluster G11-5 the most common type during 2000. Additional norovirus genetic clusters GI-3, GII-1, GII-2, GII-3, GII-6, and GII-7, were also identified, but comprised only 17/94 of norovirus genogroup II strains. Five sapovirus strains were also identified. These results highlight the divergence of norovirus strains identified in a pediatric population.

An atypical human rotavirus strain, DG8, was isolated from a 13-month-old child hospitalised with acute gastro-enteritis in Australia. The virus could not be serotyped by enzyme immunoassay (EIA) using standard reagents specific for common Group A human rotavirus G serotypes. The deduced amino acid sequence of the outer capsid glycoprotein, VP7, indicated that this strain belonged to the uncommon human serotype G8. This was confirmed by EIA incorporating a G8-specific neutralising monoclonal antibody (NMAb). The VP4 genotype of DG8 was determined as P[14], equivalent to P serotype P3B, by sequence analysis and confirmed by EIA incorporating a P3B-specific NMAb. Electrophoretic analysis of DG8 genomic dsRNA indicated that the virus exhibited a "long" electropherotype. Northern hybridisation analysis (using a whole-genome probe derived from DG8) indicated that DG8 shared overall homology with the European serotype G8 strain, HAL1166 (11 of 11 genes). In contrast, only 9 of 11 genes of DG8 hybridised with the Asian serotype G8 strain, B37, and with the bovine G8 strain, A5. Hence, DG8 displayed features reminiscent of the human serotype G8 rotaviruses isolated in Europe in the mid-1980s rather than the geographically local G8 Asian strains isolated a decade earlier. It is possible that DG8 arose through reassortment between human and bovine rotaviruses.

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