Abstract
A novel hepatitis B virus (HBV) strain (W29) was isolated from serum samples in the northwest of China. Phylogenetic and distance analyses indicate that this strain is grouped with a series of distinct strains discovered in Vietnam and Laos that have been proposed to be a new genotype I. TreeOrderScan and GroupScan methods were used to study the intergenotype recombination of this special group. Recombination plots and tree maps of W29 and these putative genotype I strains exhibit distinct characteristics that are unexpected in typical genotype C strains of HBV. The amino acids of P gene, S gene, X gene, and C gene of all genotypes (including subtypes) were compared, and eight unique sites were found in genotype I. In vitro and in vivo experiments were also conducted to determine phenotypic characteristics between W29 and other representative strains of different genotypes obtained from China. Secretion of HBsAg in Huh7 cells is uniformly abundant among genotypes A, B, C, and I (W29), but not genotype D. HBeAg secretion is low in genotype I (W29), whose level is close to genotype A and much lower than genotypes B, C, and D. Results from the acute hydrodynamic injection mouse model also exhibit a similar pattern. From an overview of the results, the viral markers of W29 (I1) in Huh7 cells and mice had a more similar level to genotype A than genotype C, although the latter was closer to W29 in distance analysis. All evidence suggests that W29, together with other related strains found in Vietnam and Laos, should be classified into a new genotype.
Highlights
The hepatitis B virus (HBV) is globally distributed, infecting approximately one-third of the world’s human population
Phylogenetic trees were generated using complete genomes and amino acid sequences of P gene products, and both trees show that W29 falls within the same sequence clade as the Vietnam and Laos strains, with this clade being separated from genotype C groups (Fig. 1)
The suggestion that this clade is a new genotype of HBV is still under dispute [17,20,22]
Summary
The hepatitis B virus (HBV) is globally distributed, infecting approximately one-third of the world’s human population. Threshold had been used for separation of the different genotypes. With more and more HBV complete sequence discovered, a threshold of 7.5% was suggested after a phylogenetic analysis and pairwise comparison of 670 complete genomes [2]. Genotypes D/G, on the other hand, seem to be scattered worldwide. In addition to these acknowledged genotypes, there’re putative genotypes that could not classify into those group above. Prior to the definition of genotypes, HBV stains can be divided into 9 serotypes, designated as ayw, ayw, ayw, ayw, ayr, adw, adw4q2, adrq+, and adrq, according to the different serological analysis results of surface antigen [9,10]. The occurrence of HBeAg negative chronic hepatitis B is genotype-specific related [11]
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