Herpesvirales

Herpesvirales
Virus classification
Group: Group I (dsDNA)
Order: Herpesvirales
Families

The Herpesvirales is an order of dsDNA viruses with eukaryotic hosts and enveloped virions, characterized by a common morphology.

Virology

All members of the order have a virion structure that consists of a DNA core surrounded by an icosahedral capsid composed of 12 pentavalent and 150 hexavalent capsomeres (T = 16). The capsid has a diameter of ~110 nanometers (nm) and is embedded in a proteinaceous matrix called the tegument, which in its turn is enclosed by a glycoprotein-containing lipid envelope with a diameter of about 200 nm.

The DNA genome is linear and double stranded, with sizes ranging between 125~290 kbp.[1] The genome contains terminal and internal reiterated sequences, with their number and disposition varying depending on the different subclades.

Species in this order infect animals: the Herpesviridae (commonly referred to as herpesviruses) are associated with mammals, birds and reptiles; the Alloherpesviridae with amphibians and fish; and the Malacoherpesviridae with bivalves.[2]

The only protein with widespread conservation amongst all members of the order, albeit only at the aminoacid level, is the ATPase subunit of the DNA terminase;[1] the latter is involved in the packaging of the DNA during virion assembly.[3]

History

The genus Herpesvirus was established in 1971 in the first report of the International Committee on Taxonomy of Viruses (ICTV) . This genus consisted of 23 viruses and 4 groups of viruses. In the second ICTV report in 1976 this genus was elevated to family level - the Herpetoviridae. Because of possible confusion with viruses derived from reptiles this name was changed in the third report in 1979 to Herpesviridae. In this report the family Herpesviridae was divided into 3 subfamilies (Alphaherpesvirinae, Betaherpesvirinae and Gammaherpesvirinae) and 5 unnamed genera: 21 viruses were listed. In 2009 the family Herpesviridae was elevated to the order Herpesvirales. This elevation was necessitated by the discovery that the herpesviruses of fish and molluscs were only distantly related to those of birds and mammals. Two new families were created - the family Alloherpesviridae which incorporates bony fish and frog viruses and the family Malacoherpesviridae which contains those of molluscs.

As of July 2017, the ICTV taxonomy indicates that the order is made up of 3 families, 3 subfamilies, 22 genera, and 103 species.

Naming system

The Herpesvirales naming system originated in 1973 and has been elaborated considerably since. The recommended naming system specified that each herpesvirus should be named after the taxon (family or subfamily) to which its primary natural host belongs. The subfamily name is used for viruses from members of the family Bovidae or from primates (the virus name ending in –ine, e.g. bovine), and the host family name for other viruses (ending in –id, e.g. equid). Human herpesviruses have been treated as an exception (human rather than hominid). Following the host-derived term, the word herpesvirus is added, followed by an Arabic number (1,2,3,...). These last two additions bear no implied meaning about taxonomic or biological properties of the virus.

Some exceptions to this system exist. A number of virus names (e.g. Epstein–Barr virus) are so widely used that it is impractical to attempt to insist on their replacement. This has led to a dual nomenclature in the literature for some herpesviruses. All herpesviruses described since this system was adopted have been named in accordance with it.

Phylogenetics

Phylogenies constructed with the conserved regions of the ATPase subunit of the DNA terminase suggest that Alloherpesviridae is the basal clade or the order, and that Herpesviridae and Malacoherpesviridae are sister clades.[4] Given the phylogenetic distances between vertebrates and molluscs, this suggests that herpesviruses were initially fish viruses and that they have evolved with their hosts to infect other vertebrates.

References

  1. 1 2 Davison, Andrew J.; Eberle, Richard; Ehlers, Bernhard; Hayward, Gary S.; McGeoch, Duncan J.; Minson, Anthony C.; Pellett, Philip E.; Roizman, Bernard; Studdert, Michael J. (2009). "The order Herpesvirales". Archives of Virology. 154 (1): 171–177. doi:10.1007/s00705-008-0278-4. ISSN 1432-8798. PMC 3552636. PMID 19066710.
  2. ↑ McGeoch, Duncan J.; Davison, Andrew J.; Dolan, Aidan; Gatherer, Derek; Sevilla-Reyes, Edgar E. (2008). DOMINGO, ESTEBAN; PARRISH, COLIN R.; HOLLAND, JOHN J., eds. Origin and Evolution of Viruses (Second Edition). London: Academic Press. pp. 447–475. ISBN 9780123741530.
  3. ↑ Selvarajan Sigamani, Sundaresan; Zhao, Haiyan; Kamau, Yvonne N.; Baines, Joel D.; Tang, Liang (June 2013). "The structure of the herpes simplex virus DNA-packaging terminase pUL15 nuclease domain suggests an evolutionary lineage among eukaryotic and prokaryotic viruses". Journal of Virology. 87 (12): 7140–7148. doi:10.1128/JVI.00311-13. ISSN 1098-5514. PMC 3676077. PMID 23596306.
  4. ↑ Rakus, Krzysztof; Ouyang, Ping; Boutier, Maxime; Ronsmans, Maygane; Reschner, Anca; Vancsok, Catherine; Jazowiecka-Rakus, Joanna; Vanderplasschen, Alain (2013). "Cyprinid herpesvirus 3: an interesting virus for applied and fundamental research". Veterinary Research. 44 (1): 85. doi:10.1186/1297-9716-44-85. ISSN 0928-4249. PMC 3850573. PMID 24073814.
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