Molecular virology of hepatitis B virus.

Hepatitis B virus (HBV) has evolved a unique life cycle that results in the production of enormous viral loads during active replication without actually killing the infected cell directly. Because HBV uses reverse transcription to copy its DNA genome, mutant viral genomes emerge frequently. Particular selection pressures, both endogenous (host immune clearance) and exogenous (vaccines and antiviral drugs), readily select out these escape mutants. Which particular viral mutations or combination of mutations directly affect the clinical outcome of infection are not known. Further studies are clearly needed to identify the pathogenic basis and clinical sequelae arising from the selection of these mutants.