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Family	00.030.  Hepadnaviridae
	Taxonomic Structure of the Family
	Family         00.030. Hepadnaviridae Genus                      00.030.0.01. Orthohepadnavirus Genus                      00.030.0.02. Avihepadnavirus Genus                      00.030.0.00. unassigned

List of Species Demarcation Criteria in the Genus

The species demarcation criteria in the genus are:
Nucleotide sequence diversity; WHV/HBV 40%; GHSV/WHV 15%; WMHBV/HBV 20%; WMHBV /WHV 30%

Differences in host range: HBV infection is limited to primates; GSHV infection has been experimentally transferred to chipmunks and woodchucks but not to several related ground squirrel species; WHV also has a narrow host range, being reported not to infect ground squirrels or other rodent species. WMHBV is transmitted to the spider monkey and, inefficiently, to chimpanzees.

A number of related viruses that clearly belong to this genus have been isolated from subhuman primates (chimpanzees, gibbons, orangutan and gorilla) and from various rodent species (Artic ground squirrels, Richardson s ground squirrels). As illustrated in Figure 4, these isolates are quite similar to assigned isolates of HBV, WHV, or GSHV (sequencing data is not available for the Richardson s ground squirrel isolate), but nothing is known about host range divergence from existing species.

List of Species in the Genus

The ICTVdB virus code and the viruses. Official virus species names are in italics. Tentative virus species names, alternative names ( ), isolates, strains, serotypes, subspecies, or rejected names are not italicized.
 
Virus codes, virus names, genome sequence accession numbers [ ] and assigned abbreviations ( ), are:

Species, their serotypes, strains and isolates

Tentative Species in the Genus

List of Species Demarcation Criteria in the Genus

The species demarcation criteria in the genus are: Nucleotide sequence diversity: HHBV/DHBV 21.6%. HHBV can be transmitted to herons but not to ducks.

A number of other less well characterized viruses have been isolated from geese and ducks with reported sequences more closely related to that of DHBV than HHBV. A virus closely related to HHBV has recently been isolated from white storks and designated Stork hepatitis B virus (STHBV). Like HHBV, STHBV has low infectivity for duck hepatocytes. STHBV may be tentatively assigned as a variant of HHBV.

List of Species in the Genus

The ICTVdB virus code and the viruses. Official virus species names are in italics. Tentative virus species names, alternative names ( ), isolates, strains, serotypes, subspecies, or rejected names are not italicized.
 
Virus codes, virus names, genome sequence accession numbers [ ] and assigned abbreviations ( ), are:

Species, their serotypes, strains and isolates

Tentative Species in the Genus

None reported.

List of Unassigned Viruses in the Family

Similarity with other Taxa

Reverse transcription as an essential step in replication is a common feature of hepadnaviruses, retroviruses and caulimoviruses. Hepadnaviruses and retroviruses also contain three major genes each with the same function and in the same order (ie corepolymerase-pre S/S and gag-pol-env respectively); a fundamental distinction is that, with hepadnaviruses, the form of the genome in extracellular virions is DNA and reverse transcription takes place during the efferent or outgoing arm of the replication cycle, while the reverse hold true for retroviruses (with the exception of the spumaviruses, in which some infectious particles appear to contain a DNA genome). Retroviruses use tRNAs as primer for the DNA minus strand, hepadnaviruses a tyrosine in the polymerase itself. The polymerase protein of hepadnaviruses does not contain a protease or integrase function. Many other aspects are distinctly different in both virus families, partly due to the extremely small size of the hepadnaviral genome and the need to efficiently exploit this restricted genetic space by using considerable overlap of both coding regions and regulatory elements.

Derivation of Names

Avi: from Latin avis, "bird",
dna: sigla for deoxyribonucleic acid,
Hepa: from Greek hepar, "liver",
Ortho: from Greek orthos, "straight".

References

Collated from VIIIth ICTV Report

Contributed by

Mason, W.S., Burrell, C.J., Casey, J., Gerlich, W.H., Howard, C.R., Kann, M., Lanford, R., Newbold, J., Schaefer, S., Taylor, J.M. and Will, H.

Version 4 is based on Virus Taxonomy, Classification and Nomenclature of Viruses, 8th ICTV Report of the International Committee on Taxonomy of Viruses. Fauquet, CM, Mayo, MA, Maniloff, J, Desselberger, U, and Ball, LA (EDS) (2005) Elsevier/Academic Press, pp. 1259.

Additional References

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