Hepatitis B virus: molecular virology and common mutants.

A high rate of viral turnover, combined with an error-prone polymerase, results in a very high frequency of mutational events during hepatitis B virus replication. Mutants may accumulate, particularly in individuals at advanced stages of persistent infection and with antibody- and cell-mediated immune responses to the virus. Specific mutants may be selected from these populations, especially by antibody and cytotoxic T lymphocyte responses and by antiviral therapy. In some cases, the mutants may be associated with especially severe acute hepatitis (including acute liver failure) and the development of sequelae such as cirrhosis and hepatocellular carcinoma. Antiviral resistance poses a challenge to therapy that might be overcome by the use of combinations of antiviral drugs.