There are two main classes of encapsidation signals in avian HBV viruses - Duck hepatitis B virus (DHBV) and Heron hepatitis B virus (HHBV) like. DHBV is used as a model to understand human HBV. Although studies have shown that the HHBV epsilon has less pairing in the upper stem than DHBV, this pairing is not absolutely required for DHBV infection in ducks.