Hepatitis C virus types 7, 8 and 9 should be classified as type 6 subtypes.
Tokita et al. reported the identification of hepatitis C virus type 7, 8 and 9 in Southeast Asia, based on the unweighed pair-group method with the arithmetic mean, a method that may not be appropriate when the nucleotide substitution rate is not constant over time. To determine more accurately the relationship of these proposed types 7, 8, and 9 with other types, a more appropriate approach, the neighbor-joining method, was applied to re-evaluate the phylogenetic relationship. A total of 660 HCV sequences, including the reported sequences, were collected from DNA databases. For every region, the nucleotide substitution rate was estimated by the 6-parameter method, and phylogenetic trees were constructed using the neighbor-joining method. The results of this analysis indicate that the newly proposed HCV types 7, 8 and 9 should be classified as type 6 subtypes. HCV type 6 appears to be diversified.