Genotypes and Genetic Variability of Hepatitis B Virus

Abstract

Sequence heterogeneity is a feature of hepatitis B virus (HBV), the prototype member of the family Hepadnaviridae. Based on an intergroup divergence of greater than 7.5% across the complete genome, HBV has been classified phylogenetically into 9 genotypes, A-I, with a putative 10th genotype ‘J', isolated from a single individual. With between approximately 4 and 8% intergroup nucleotide divergence across the complete genome and good bootstrap support, genotypes A-D, F, H, and I are classified further into subgenotypes. There is a broad and highly statistically significant correlation between serological subtypes and genotypes, and in some cases, serological subtypes can be used to differentiate subgenotypes. The genotypes, and certain subgenotypes, have distinct geographical distributions and are important in both the clinical manifestation of infection and response to antiviral therapy. HBV genotypes/subgenotypes and genetic variability of HBV are useful in epidemiological and transmission studies, tracing human migrations, and in predicting the risk for the development of severe liver disease and response to antiviral therapy. Moreover, knowledge of the genotype/subgenotype is important in implementing preventative strategies. Thus, it is crucial that new strains are correctly assigned to their respective genotype/subgenotype and consistent, unambiguous, and generally accepted nomenclature is utilized.

Serological and molecular epidemiological outcomes after two decades of universal infant hepatitis B virus (HBV) vaccination in Nunavut, Canada

“…It is to note, a recent review has reclassified genotype B subgenotypes, specifically reducing the total number of subgenotypes of genotype B to B1 to B5 [55]. The Inuit population of the western circumpolar Arctic region were originally associated with genotype B6 infection, which has been redesignated as genotype B5.…”

Diagnosis of hepatitis B

“…Viral capsid bears viral genome and DNA polymerase that has reverse transcriptase activity. HBV genome comprise a circular, partly double-stranded DNA and has four open reading frames overlapped: (I) S that encodes for surface proteins (HBsAg); (II) pre-C/C for hepatitis B e antigen (HBeAg) and core protein (HBcAg); (III) P for polymerase including reverse transcriptase; (IV) X that encodes for a transcriptional transactivator factor (HBxAg) (2). The covalently closed circular DNA (cccDNA) is the transcriptional template of HBV and stays inside the hepatocyte nucleus as a mini-chromosome (3).…”

Single-Molecule Sequencing Reveals Complex Genome Variation of Hepatitis B Virus during 15 Years of Chronic Infection following Liver Transplantation

“…The approximately 3,200-nucleotide (nt) genome consists of four overlapping, frame-shifted open reading frames (ORF) encoding the polymerase (P), envelope (ENV), X, and core (C) proteins. HBV can be divided into nine genotypes, labeled genotypes A to I, with a further putative genotype (genotype J) being proposed (4). With the exception of genotypes E and G, all genotypes can be further classified into subgenotypes.…”