I had a question. Does HDV occur if you have high amount of HBsAG? Or it is a seperate infection which occurs after you have been infected with someone who has Hep D?
For example someone with high amount of HBsAG i.e 125000 in hep b will have HDV?
HDV is a separate virus from a different viral family than HBV. What is different about this virus is that it does not contain the genetic information for all of the proteins it needs to reproduce itself. It is missing the information to make its own surface (envelope) protein to help in its secretion from infected cells and also to improve its ability to infect new cells.
In the case of HDV, this virus has evolved to prefer infecting cells which are already infected with HBV so that it can use the HBsAg protein already being made from HBV infection. Having access to HBsAg inside the cell allows the forming core of HDV (which has a complicated technical name: the HDV ribonucleoprotein) to acquire an envelope (and the HBsAg protein) and to be secreted using the same machinery as HBV subviral particles. It also allows HDV access to the same receptor on the cell surface which HBV can use to improve the efficiency of infection.
So HDV infection is not a function of the amount of HBsAg present but rather a “satellite” infection of HBV caused by co-infection of HBV and HDV.