Hepatitis delta virus (HDV) is the only known human disease agent to resemble viroids at present.
Hepatitis delta virus is the only known species in the genus Deltavirus, family Kolmioviridae.
The agent appears to be intermediate between ‘classical viruses’ and viroids.
HDV has a very small circular RNA genome (~1700 nucleotides) compared to most viruses, although it is somewhat larger than viroids.
HDV is considered to be a subviral satellite because it can propagate only in the presence of the hepatitis B virus (HBV).
HDV is a subviral satellite virus and it can propagate only in the presence of the hepatitis B virus (HBV).
HDV depends on HBV for packaging, release, and transmission.
HDV only codes for its own attachment protein.
Extracellular HDV virions contain the genomic HDV RNA, a single-stranded negative-sense and covalently closed circular RNA molecule, which is associated with the HDV-encoded delta antigen forming a ribonucleoprotein complex, and enveloped by the HBV surface antigens.