Hepatitis B and C

The Hepatitis B virus (HBV) genome has a circular, partially double stranded DNA. It belongs to the hepadnaviridae family of viruses and replicates within infected liver cells. The HBV is not a cytotoxic virus. Viral nucleocapsid antigens, HBeAg and/or HBcAg, expressed with HLA class I antigens on the hepatocytes plasma membrane are believed to be the major targets for activated cytotoxic T cells. The elimination of infected cells seems to be dependent on cellular immune responses and it is the immune response that causes the hepatitis. Host factors, mainly the immune system response, and intrinsic viral factors might play an important role in the viral escape from elimination in chronic disease. HBeAg seems to be important for the induction of T-cell tolerance to nucleocapsid antigens co-expressed with the major histocompatibility complex at the hepatocyte surface. HBV, by secreting the protein e, induces immunological tolerance in the host and causes chronic infection in 5-10% of acute hepatitis B cases. HBV is transmitted by the exchange of blood or body fluids. Many cases of acute hepatitis B occur sporadically with no known source and studies have shown that prior unrecognised infection is common.