Distribution of genotype/subtype and mutational spectra of the surface gene of hepatitis B virus circulating in Hanoi, Vietnam

In order to ascertain the molecular epidemiological features and mutational spectra of hepatitis B virus (HBV) in Hanoi, Vietnam, direct sequencing of the 219-nucleotide fragment of the surface (S) gene of HBV from the sera of 40 patients mostly with chronic hepatitis were carried out. The samples were classified into genotypes by phylogenetic and genotype-specific analysis, and subtypes by the deduced amino acid sequences. The results showed that genotype B with ayw1 was predominant genotype/subtype (63%), followed by genotype C with adr (18%). The quasi-species nature of the HBV in the sera was observed in 24 of 40 samples examined. One sample (HN109) showed mixture of genotypes B and C. Among 26 amino acid substitutions, 16 were the variants and the remainders were mutations. In the "a" determinant region, three mutations with methionine to leucine (L) changes at the 133 amino acid residue were in the first loop and no mutations were in the second loop. A new mutation, threonine to methionine at 126 amino acid residue, was observed in one sample. In conclusion, the analysis of the S gene region of HBV showed that in Hanoi, genotype B with ayw1 was prevalent and the quasi-species nature of HBV was also common.