HEPATITIS-D VIRUS

The hepatitis D virus (HDV) relies on the helper hepatitis B virus (HB V) for the provision of its envelope, which consists of hepatitis B su rface antigen (HBsAg). The RNA genome of HDV is a circular rod-like st ructure due to its extensive intramolecular base-pairing. HDV-RNA has ribozyme activity which includes autocatalytic cleavage and self-ligat ion properties, essential in virus replication via the rolling circle mechanism. Replication of the RNA is thought to be effected by cellula r RNA polymerase II. Hepatitis D antigen (HDAg) is the only protein en coded by HDV-RNA and its long and short forms have a regulatory role i n the replication and morphogenesis of the virus. Superinfected HBV ca rriers who become chronically infected with HDV are at increased risk of developing cirrhosis. Attempts to treat such carriers with interfer on have not been particularly successful. In recent years the epidemio logy of HDV has changed primarily due to the impact of HBV vaccination in preventing an increase in :he pool of susceptible individuals. (C) 1998 John Wiley & Sons, Ltd.