THE HEPATITIS-DELTA VIRUS - A SINGULAR REPLICATION

The human hepatitis delta virus (HDV) is an unusual infectious agent of animals showing many similarities to pathogenic RNAs of plants. Some unique and intriguing features have been assigned to HDV : the envelope of an helper virus, the hepatitis B virus (HBV), is needed for the assembly of HDV particles; its genome encodes a solitary protein, the delta antigen, which is essential to the regulation of the viral genome replication and the viral genome packaging into HBV envelope. In fact two forms of the delta antigen appear sequentially in the infected cells : the small form, that positively regulated HDV replication, the large form, that negatively regulate HDV replication but promotes the particle assembly into HBV envelope. The possibility remains that HDV could be a prototype for a class of yet unknown infectious agents, that might be involved in other diseases of animals.