HEPATITIS-C VIRUS VARIANTS FROM THAILAND CLASSIFIABLE INTO 5 NOVEL GENOTYPES IN THE 6TH (6B), 7TH (7C, 7D) AND 9TH (9B, 9C) MAJOR GENETIC GROUPS

Nine (10%) out of 90 hepatitis C virus (HCV) isolates from hepatitis p atients and commercial blood donors in Thailand were not classifiable into any of genotypes I/1a, II/1b, III/2a, IV/2b, V/3a or VI/3b by RT- PCR with type-specific primers deduced from the HCV core gene. These i solates were sequenced over a 1.6 kb stretch of the 5'-terminal sequen ce and 1.1 kb of the 3'-terminal sequence covering 30% of the entire g enome. Based on two-by-two comparison and phylogenetic analyses of the nine Thailand isolates among themselves and with known full or partia l sequences of previously reported HCV isolates, the Thailand isolates were classified into five genotypes not reported previously, viz. 6b, 7c, 7d, 9b and 9c. Along with HCV isolates reported already, they mak e at least nine major genetic groups of HCV which further break down i nto at least 28 genotypes with sequence similarity in the E1 gene (576 bp) of less than or equal to 80%. As many more HCV isolates of distin ct genotypes are expected to be found throughout the world, it will be come increasingly difficult to classify them by comparison of any part ial sequences of the genome. Complete sequence data will be required f or the full characterization and classification of HCV genotypes.