Persistence of hepatitis B virus and establishment of delta virus infection.

A typical feature of an infection with the hepatitis B virus (HBV) is the development of a persistent infection manifested by a chronic carriership of hepatitis B antigen (HBsAg). There is a marked geographical variation in the frequency of the chronic HBsAg carrier state. The replication of the HBV is unique for a DNA virus and has functional characteristics of a retrovirus, i.e. replication of viral DNA through an RNA intermediate. In addition to episomal viral DNA involved in virus replication other episomal forms and integrated viral DNA have been found in infected cells. The integrated HBV DNA in liver cells is an essential factor in the development of hepatocellular carcinoma. Many epidemiological studies have made it clear that age, sex and immunological status are important factors predisposing to the development of chronic infection. Hepatitis D virus (HDV) is a distinct infectious agent but it is defective as it requires the helper function of HBV for its replication. There are two possible modes of infection, either a coinfection, i.e. simultaneous infection with HBV and HDV, or a superinfection, i.e. a chronic HBsAG carrier who becomes infected with HDV. The majority (70-90%) of all superinfections take a chronic course.