An aberrant genotype revealed in recombinant hepatitis B virus strains from Vietnam.

Six genotypes of hepatitis B virus (HBV) have been described. However, relatively few complete genomes originating from East Asia, where most of the world's HBV carriers live, have been studied. We analysed five complete HBV genomes of Vietnamese origin, which in our previous studies had produced atypical genotyping patterns. All five strains had HBsAg sequences with markers for serotype adw. In phylogenetic tree analysis, two of the genomes clustered with genotype C, and three clustered on a separate branch between genotypes A, B and C, suggesting a new genotype. However, these three strains showed signs of recombination in similarity plot and bootscanning analysis. Phylogenetic tree analysis of two segments separately supported recombination between genotype C and a putative new genotype (or possibly a subgroup of genotype A). The segment between nt 1801 and 2865 was clearly of genotype C origin, while the major part of the genome (nt 2866-1800) was placed on a branch close to genotype A. The findings encourage further study of genotypes and recombination in HBV from this geographical region.