Hepatitis delta virus (HDV) is a subviral agent that uses the envelope proteins of hepatitis B virus (HBV) to complete its life cycle. Thus HDV infections are only found in association with HBV.

At the 2007 International HBV Meeting at Rome in September, a special one-day satellite meeting was held to honor Dr. Mario Rizzetto and celebrate the 30th anniversary of the discovery of HDV. Eleven presentations covered the range from the molecular biology of HDV to the consequences for HDV infected individuals.

Included was a talk from Dr. Ricardo Flores, in which he showed the remarkable similarities between HDV replication and many families of subviral agents known as viroids that cause disease in plants. Dr. Robert Purcell, one of the investigators working with Dr. Rizzetto on the original discovery of HDV, used state-of-the art gene array analyses of the consequences of HDV infections of the liver. In contrast to HBV infections that seem to slip under the early detection by the host innate immune response, he showed that the additional presence of HDV leads to specific activation of the innate response, with the expression of genes that correlate with the increased liver damage.

Overall, it was realized that we still have much yet to learn about the mechanism by which HDV is replicated. In addition, since HDV and HBV share the same envelope proteins, it is likely that they attach and enter liver cells by very similar mechanisms. Thus, continued studies with HDV might help clarify the important unanswered questions relating to the mechanisms of virus attachment and entry.