Hepatitis C virus (HCV) shows substantial nucleotide sequence diversity distributed throughout the viral genome, with many variants showing only 68 to 79 % overall sequence similarity to one another. Phylogenetic analysis ofnucleofide sequences derived from part of the gene encoding a non-structural protein (NS-5) has provided evidence for six major genotypes of HCV amongst a worldwide collection of 76 samples from HCV-infected blood donors and patients with chronic hepatitis. Many of these HCV types comprised a number of more closely related subtypes, leading 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 which only the six major HCV types, but not subtypes, could be differentiated. A new nomenclature for HCV variants is proposed in this communication that reflects the twotiered nature of sequence differences between different viral isolates. The scheme classifies all known HCV variants to date, and describes criteria that would enable new variants to be assigned within the classification as they are discovered.
We are researchers who have published analyses of nucleic acid sequence variation of hepatitis C virus (HCV) and associated virological and clinical significance. We are concerned that our investigations are hampered by the lack of a consensus nomenclature for variants of HCV and that this leads to confusion when results from different laboratories are compared. Furthermore, because there are no consistently applied criteria by which new genotypes are defined, investigators assign new type descriptions to novel sequence variants on an ad hoc basis without agreement from
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