Hepatitis delta: the virus and the disease.

In general, the biological and structural properties of the hepatitis delta virus resemble those of the viroids and related satellite RNA viruses of plants. This resemblance has been strengthened by the discovery that, in analogy to the self-cleaving of some plant RNA viruses, hepatitis delta virus RNA possesses autocleaving and autoligating sites located in sequences that are homologous with highly conserved domains in the viroids. The catalytic properties identify the hepatitis delta virus as the first mammalian ribozyme. The current interpretation of the pathobiology of delta hepatitis rests on the postulates that the hepatitis delta virus invariably requires hepatitis B virus for infection and is highly pathogenic. Accordingly, delta hepatitis is thought to occur when hepatitis delta virus coinfects with hepatitis B virus or when it superinfects hepatitis B virus carriers. However, new evidence from the liver transplantation model suggests that hepatitis delta virus is capable of establishing latent, asymptomatic infections without the apparent assistance of hepatitis B virus: in this model, disease was only reactivated when hepatitis B virus also returned to the graft. Thus, hepatitis B virus superinfection on a latent hepatitis delta virus state may be a third pathobiological mechanism conducive to delta hepatitis.