Hepatitis C virus variants from Thailand classifiable into five novel genotypes in the sixth (6b), seventh (7c, 7d) and ninth (9b, 9c) major genetic groups

1 Immunology Division, Jichi Medical School, Tochigi-Ken 329-04, Japan 2 Division of Gastroenterology, Siriraj Hospital, Mahidol University, Bangkok, Thailand 3 Division of Nephrology, Siriraj Hospital, Mahidol University, Bangkok, Thailand 4 Japanese Red Cross Saitama Blood Center, Saitama-Ken 338, Japan 5 Department of Medical Sciences, Toshiba General Hospital, Tokyo 140, Japan and 6 Mita Institute, Tokyo 108, Japan Nine (10%) out of 90 hepatitis C virus (HCV) isolates from hepatitis patients 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 isolates were sequenced over a 1.6 kb stretch of the 5'-terminal sequence and 1.1 kb of the 3'-terminal sequence covering 30% of the entire genome. Based on two-by-two comparison and phylogenetic analyses of the nine Thailand isolates among themselves and with known full or partial 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 make at least nine major genetic groups of HCV which further break down into at least 28 genotypes with sequence similarity in the E1 gene (576 bp) of 80%. As many more HCV isolates of distinct genotypes are expected to be found throughout the world, it will become increasingly difficult to classify them by comparison of any partial sequences of the genome. Complete sequence data will be required for the full characterization and classification of HCV genotypes. * Author for correspondence. Fax +81 285 44 1557. Received 14 November 1994; accepted 17 February 1995.