CLASSIFICATION OF HEPATITIS-C VIRUS INTO 6 MAJOR GENOTYPES AND A SERIES OF SUBTYPES BY PHYLOGENETIC ANALYSIS OF THE NS-5 REGION

Hepatitis C virus (HCV) shows substantial nucleotide sequence diversit y distributed throughout the viral genome, with many variants showing only 68 to 79% overall sequence similarity to one another. Phylogeneti c analysis of nucleotide sequences derived from part of the gene encod ing a non-structural protein (NS-5) has provided evidence for six majo r genotypes of HCV amongst a worldwide collection of 76 samples from H CV-infected blood donors and patients with chronic hepatitis. Many of these HCV types comprised a number of more closely related subtypes, l eading to a current total of 11 genetically distinct viral populations . Phylogenetic analysis of other regions of the viral genome produced relationships between published sequences equivalent to those found in NS-5, apart from the more highly conserved 5' non-coding region in wh ich only the six major HCV types, but not subtypes, could be different iated. A new nomenclature for HCV variants is proposed in this communi cation that reflects the two-tiered nature of sequence differences bet ween different viral isolates. The scheme classifies all known HCV var iants to date, and describes criteria that would enable new variants t o be assigned within the classification as they are discovered.