Genetic and antigenic characterization of a serotype G6 human rotavirus isolated in Melbourne, Australia.

An unusual rotavirus strain, MG6, was isolated from a 16-month-old child admitted to hospital with acute gastroenteritis. The virus could not be serotyped (G-typed) by enzyme immunoassay using standard reagents specific for common serotypes of human Group A rotaviruses. Nucleotide sequencing of cDNA derived from the gene encoding the outer capsid protein, VP7, and deduction of the VP7 amino acid sequence indicated that this strain belonged to serotype G6, a serotype normally associated with viruses causing disease in cattle. This was confirmed by polymerase chain reaction typing and enzyme immunoassay using a G6-specific monoclonal antibody. The VP4 genotype of MG6 was determined by hybridization of its VP4 cDNA to genomic RNA isolated from standard strains of defined P-types. This analysis, confirmed by deduced amino acid sequence analysis, classified MG6 into the novel genotype P13. MG6, therefore, is related to the previously described G6P13 human strain PA169, isolated in Italy. The emergence of strain MG6, the first human G6 rotavirus identified in Australia, provides further evidence of reassortment between human and animal rotaviruses.