While clearly HDV is not a plant virus, regardless of some
similarity to a tomato virus??, it is interesting to note that it is
the closest thing to the animal equivalent of a viroid- a class of
organisms to date only found in plants. However, strictly speaking,
HDV is not a true viroid, despite it similar replicative mechanisms,
because a portion of the HDV RNA encodes a protein- whereas viroids
encode no proteins at all.