THE HEPATITIS-DELTA VIRUS - A SINGULAR RE PLICATION

The human hepatitis delta virus (HDV) is an unusual infectious agent o f animals showing many similarities to pathogenic RNAs of plants. Some unique and intriguing features have been assigned to HDV : the envelo pe 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 genom e replication and the viral genome packaging into HBV envelope. In fac t two forms of the delta antigen appear sequentially in the infected c ells : 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, tha t might be involved in other diseases of animals.