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Complete nucleotide sequences of 19 hepatitis B virus (HBV) isolates of genotype A (HBV/A) were determined and analysed along with those of 20 previously reported HBV/A isolates. Of the 19 HBV/A isolates, six including three from Japan and three from the USA clustered with the 14 HBV/A isolates from Western countries. The remaining 13 isolates including four from The Philippines, two from India, three from Nepal and four from Bangladesh clustered with the six HBV/A isolates reported from The Philippines, South Africa and Malawi. Due to distinct epidemiological distributions, genotype A in the 20 HBV isolates was classified into subtype Ae (e for Europe), and that in the other 19 into subtype Aa (a for Asia and Africa) provisionally. The 19 HBV/Aa isolates had a sequence variation significantly greater than that of the 20 HBV/Ae isolates (2.5+/-0.3 % vs 1.1+/-0.6 %, P<0.0001); they differed by 5.0+/-0.4 % (4.1-6.4 %). The double mutation (T1762/A1764) in the core promoter was significantly more frequent in HBV/Aa isolates than in HBV/Ae isolates (11/19 or 58 % vs 5/20 or 25 %, P<0.01). In the pregenome encapsidation (epsilon) signal, a point mutation from G to A or T at nt 1862 was detected in 16 of the 19 (84 %) HBV/Aa isolates but not in any of the 20 HBV/Ae isolates, which may affect virus replication and translation of hepatitis B e antigen. Subtypes Aa and Ae of genotype A deserve evaluation for any clinical differences between them, with a special reference to hepatocellular carcinoma prevalent in Africa.

To investigate the genetic changes in hepatitis E virus (HEV) strains in the Kathmandu valley of Nepal, we compared the 412 nt sequence within open reading frame 2 of HEV among HEV isolates recovered from 16 patients in 1999, 14 patients in 2000 and 38 patients in 2002, and additional isolates recovered from 48 patients in 1997 whose nucleotide sequences have been previously published. All 116 HEV-viraemic samples were genotyped as 1 and subtyped further as 1a (n=85, 73 %), 1c (n=29, 25 %) and mixed infection of 1a and 1c (n=2, 2 %): subtype 1c was detected only in 1997. Among the 1a isolates, nucleotide sequence identity with the representative 1a isolate of Ne131-1997 was 96.4+/-2.4 % (mean+/-SD) in 1997, 93.9+/-1.7 % in 1999, 92.2+/-1.0 % in 2000 and 91.7+/-0.5 % in 2002, indicating gradual diversification of HEV sequences. When phylogenetic analysis of the 87 subtype 1a isolates was performed, they further segregated into five clusters, with two predominant clusters of 1a-2 and 1a-3: the annual frequency of cluster 1a-2 isolates decreased from 63 % in 1997, to 50 % in 1999, to 7 % in 2000 and no cases in 2002; cluster 1a-3 isolates were observed in all four years and its annual frequency increased from 5 % in 1997 to 95 % in 2002. Of the remaining three clusters, cluster 1a-1 was detectable only in 1997 and clusters 1a-4 and 1a-5 emerged in 2000 and 2002, respectively. These results indicate that genetic changes and take over of HEV strains may contribute to the genetic variability of HEV in the community.

Five isolates of hepatitis C virus (HCV) RNA from patients with chronic liver disease in Nepal were not classifiable into the known genotypes I/1a, II/1b, III/2a, IV/2b or V/3a using PCR with type-specific primers deduced from the HCV core gene. Their nucleotide sequences were determined for the 5'-terminal 1.5 kilobases and 3'-terminal 1.2 kilobases, covering 30% of the entire genome, and compared with each other and with reported sequences of HCV isolates of various genotypes. They were more similar to a reported HCV isolate (NZL1) of genotype V/3a (in 81.6 to 84.1% of their nucleotides and 85.7 to 88.7% of the deduced amino acid sequence) compared with the genotypes I/1a to IV/2b (in 69.3 to 74.7% and 72.3 to 77.4%, respectively). Hence they were considered to be variants of the third major group (group 3). The five HCV isolates shared 81.3 to 85.2% of nucleotide sequence and 85.4 to 89.3% of deduced amino acid sequence. Thus they were substantially different from each other. One of them was classified as genotype VI/3b due to an 88.2% similarity in nucleotide sequence to that of the reported HCV isolates of this genotype, whereas the remaining four were classified into provisional genotypes 3c, 3d, 3e and 3f. These HCV variants have evolved and remained in Nepal, and have not been observed in the other areas of the world.