Hepatitis delta virus: A fascinating and neglected pathogen

Table 1 Similarities and differences between hepatitis delta virus and plant viroids

HDV (1700 nt)	Pospiviroidae (200-400 nt)	Avsunviroidae (200-400 nt)
Circular ssRNA	Circular ssRNA	Circular ssRNA
Extensive intramolecular base pairing	Extensive intramolecular base pairing	Extensive intramolecular base pairing
A DNA-directed RNA polymerase makes both plus and minus strands	A DNA-directed RNA polymerase makes both plus and minus strands	A DNA-directed RNA polymerase makes both plus and minus strands
Encodes for protein	No proteins encoded	No proteins encoded
Virion maturation depends on a helper virus	Replication does not depend on the presence of a helper virus	Replication does not depend on the presence of a helper virus
Symmetric rolling circle RNA replication	Asymmetric rolling circle RNA replication	Symmetric rolling circle RNA replication
Replicates in the nucleus	Replicates in the nucleus	Replicates in chloroplasts
Ribozyme activity	No ribozyme activity	Ribozyme activity

HDV: Hepatitis delta virus.