Hepatitis C virus (HCV) subtype prevalence in Chiang Mai, Thailand, and identification of novel subtypes of HCV major type 6.

Subtype analysis of hepatitis C viruses (HCVs) obtained from patients with chronic liver disease in Chiang Mai, Thailand, was performed. Of 46 HCV isolates, 13 (28%) were shown to belong to HCV subtype 3a (HCV-3a), 10 (22%) to belong to HCV-1a, 7 (15%) to belong to HCV-1b, 1 (2%) to belong to HCV-3b, and 1 (2%) to belong to a variant group, as determined from partial nucleotide sequences of the NS5B region of the viral genome. Analysis of 5' untranslated region sequences identified five other isolates (11%) of HCV type 1 and two other isolates (4%) of type 3. Detailed phylogenetic positions for the variant described above and those previously obtained from blood donors and drug addicts in Chiang Mai were determined by a six-parameter neighbor-joining method on the basis of core, E1, and NS5B region sequences. The results revealed that those sequence variants represent novel subtypes of HCV type 6. The HCV type 6 isolates appear to be antigenically different from isolates of HCV types 1 and 2, as determined by a serotyping method that utilizes recombinant peptides corresponding to a portion of the NS4 protein. The significance of subtype analysis around this area is discussed.