Differential distribution of hepatitis C virus subtypes in Asia: comparative study among Thailand, Indonesia, the Philippines and Japan.

Hepatitis C virus (HCV) is currently classified into at least six major genotypes, each of which is further divided into a number of subtypes. It has been reported that prevalence of each subtype varies among different geographical regions of the world and that severity of liver disease and sensitivity to interferon treatment varies with different subtypes. The purpose of this study was to determine and compare the prevalence of each subtype among HCV isolates in different areas in Asia such as southern (Hat Yai) and northern (Chiang Mai) parts of Thailand, Indonesia (Surabaya), the Philippines (Manila) and Japan (Kobe). Sera were obtained from various groups of patients and tested for antibodies against HCV using second and/or third generation ELISA kits. RNA was extracted from anti-HCV-positive sera and reverse-transcribed into cDNA. The cDNA-preparations were subjected to nested PCR to amplify NS5B and 5'-untranslated region (5'UTR) sequences. Amplified fragments were sequenced and subtypes of the isolates were determined based on sequence similarities with reported sequences. In Chiang Mai and Hat Yai, Thailand, HCV-3a, HCV-1a and HCV-1b were common in various populations. HCV type 6 variants were commonly found among blood donors and drug addicts in Chiang Mai, but not in Hat Yai. In Surabaya, Indonesia, HCV-2a was frequently detected in blood donors, but less frequently in patients with chronic liver disease. In blood donors, HCV-1a, HCV-1b and HCV-1d were more strongly associated with elevation of serum aminotransferase levels than HCV-2a. HCV-1a was significantly more common in patients on maintenance hemodialysis than in blood donors or patients with chronic liver disease. HCV-1d was detected exclusively in Indonesia. Another unique subtype HCV-3g was found also in Indonesia, though less frequently than HCV-1d. In the Philippines, a vast majority of the isolates were either HCV-1a or HCV-1b. Thus, HCV subtype prevalence varies among different regions of Asia.