Hepatitis B Virus

The hepatitis B virus (HBV) is the prototype member of a family of hepatotropic DNA viruses, the Hepadnaviridae, that replicate by reverse transcription of an RNA pregenome. HBV infects humans, whereas other hepadnaviruses infect mammals (orthohepadnaviruses) or birds (avihepadnaviruses) (Schaefer, 2007a). HBV comprises eight genotypes (A to H) with distinct virological characteristics and geographic distributions (Kramvis et al., 2005; Schaefer, 2007a; see Section 1.2.3). Each genotype differs from the others by more than 8% of its nucleotide sequence. Genotypes may influence the disease caused, although further analysis of this association is required. The variability of the HBV genome may be further increased by recombination among genotypes, especially B/C and A/D. HBV genotypes, with the exception of genotypes E and G, are divisible into subgenotypes. Each subgenotype differs from the others by more than 4% of its nucleotide sequence. The number of subgenotypes per genotype described to date ranges from three to five (Kramvis et al., 2005; Schaefer, 2007a).