PREVALENCE OF HEPATITIS-C VIRUS SEQUENCE VARIANTS IN SOUTH-EAST ASIA

The nature and distribution of hepatitis C virus (HCV) genotypic varia nts present in south-east Asia have not been extensively investigated. We analysed HCV RNA obtained from 67 clinical serum samples from Sing apore, Thailand, Indonesia, the Philippines and South Korea. All sampl es were amplified by semi-nested RT-PCR and the nucleotide sequence de termined for four regions within the E1, E2/NS1, NS4 and NS5 genes. Ea ch isolate had a unique nucleotide and deduced amino acid sequence, co nsistent with the genetic heterogeneity of this virus. There was remar kably little amino acid sequence variation between isolates of the sam e genotype, apart from variable domains within putative envelope glyco proteins that are likely to be under immune pressure. All isolates cou ld be classified according to the currently recognized genotypes of HC V, with the exception of one Singapore isolate that defined a new grou p 3 subtype. The 1b genotype, which predominates in Japan, was the mos t widely distributed genotype and accounted for 58% of all isolates se quenced. Regional variations in HCV genotype distribution were observe d, with type 3a being found almost exclusively in Thailand. By contras t, the la genotype, which predominates in the USA was the most prevale nt genotype in the Philippines. Genotype la was found less commonly am ong the Thai isolates, presumably having been introduced from the West in stored blood products or by sporadic transmission. The significant prevalence of HCV types 2 and 3 restates the need for variant genotyp es to be included in immunodiagnostic and vaccine development strategi es. This study reveals that the 1b genotype of HCV, previously found t o be the major variant present in east Asia, also predominates in the south-east Asian region, and may be the major HCV type found worldwide .