Editing Virus classification (section)

==ICTV classification==
[[File:Comparison 1991 and 2019 virus taxonomy ICTV.webp|thumb|Comparison 1991 and 2018b virus taxonomy by ICTV|upright=1.4]]

The [[International Committee on Taxonomy of Viruses]] began to devise and implement rules for the naming and classification of viruses early in the 1970s, an effort that continues to the present. The ICTV is the only body charged by the [[International Union of Microbiological Societies]] with the task of developing, refining, and maintaining a universal virus taxonomy, following the methods set out in the International Code of Virus Classification and Nomenclature.<ref name=ictvcode>{{cite web|url=https://ictv.global/about/code|title=The International Code of Virus Classification and Nomenclature (ICVCN), March 2021 edition |publisher=International Committee on Taxonomy of Viruses|access-date=6 January 2024}}</ref><ref>{{cite journal | vauthors = Lefkowitz EJ, Dempsey DM, Hendrickson RC, Orton RJ, Siddell SG, Smith DB | title = Virus taxonomy: the database of the International Committee on Taxonomy of Viruses (ICTV) | journal = Nucleic Acids Research | volume = 46 | issue = D1 | pages = D708–D717 | date = January 2018 | pmid = 29040670 | pmc = 5753373 | doi = 10.1093/nar/gkx932 }}</ref> The system shares many features with the classification system of cellular [[organism]]s, such as [[taxon]] structure. However, some differences exist, such as the universal use of italics for all taxonomic names, unlike in the [[International Code of Nomenclature for algae, fungi, and plants]] and [[International Code of Zoological Nomenclature]].

Viral classification starts at the level of realm and continues as follows, with the taxonomic suffixes in parentheses:<ref name=ictvcode />

:[[Realm (virology)|Realm]] (''-viria'')
::Subrealm (''-vira'')
:::[[Kingdom (biology)#Viruses|Kingdom]] (''-virae'')
::::Subkingdom (''-virites'')
:::::[[Phylum]] (''-viricota'')
::::::Subphylum (''-viricotina'')
:::::::[[Class (biology)|Class]] (''-viricetes'')
::::::::Subclass (''-viricetidae'')
:::::::::[[Order (biology)|Order]] (''-virales'')
::::::::::Suborder (''-virineae'')
:::::::::::[[Family (biology)|Family]] (''-viridae'')
::::::::::::Subfamily (''-virinae'')
:::::::::::::[[Genus]] (''-virus'')
::::::::::::::Subgenus (''-virus'')
:::::::::::::::[[Species]]

In parallel to the system of [[binomial nomenclature]] adopted in cellular species, the ICTV has recently (2021) mandated that new virus species be named using a binomial format (''Genus species'', e.g. ''[[SARS-related coronavirus|Betacoronavirus pandemicum]]''), and that pre-existing virus species names be progressively replaced with new names in the binomial format.<ref>{{cite journal |first1=Peter J. |last1=Walker |first2=Stuart G. |last2=Siddell |first3=Elliot J. |last3=Lefkowitz |display-authors=etal |title = Changes to virus taxonomy and to the International Code of Virus Classification and Nomenclature ratified by the International Committee on Taxonomy of Viruses (2021) | journal = Archives of Virology | volume = 168 | issue = 9| pages = 2633–2648 | date = 6 July 2021 | pmid = 34231026| pmc = | doi = 10.1007/s00705-021-05156-1 |hdl = 10362/134245 |hdl-access = free }}</ref> A mid-2023 review of the status of this changeover stated: "...a large number of proposals [concerning virus nomenclature, submitted to the ICTV Executive Committee (EC) for its consideration] renamed existing species for compliance with the recently mandated binomial nomenclature format. As a result, 8,982 out of the current 11,273 species (80%) now have binomial names. The process will be concluded in 2023, with the remaining 2,291 species being renamed."<ref>{{cite journal |first1=F.M. |last1=Zerbini |first2=S.G. |last2=Siddell |first3=E.J. |last3=Lefkowitz |display-authors=etal |title = Changes to virus taxonomy and the ICTV Statutes ratified by the International Committee on Taxonomy of Viruses (2023) | journal = Archives of Virology | volume = 168 | issue = article no. 175 | date = 10 June 2023 |page=175 | pmid = 37296227| pmc =10861154 | doi = 10.1007/s00705-023-05797-4 }}</ref>

As of 2025, all levels of taxa except subrealm, subkingdom, and subclass are used. Seven realms, one ''[[incertae sedis]]'' class, 25 ''incertae sedis'' families, and two ''incertae sedis'' genera are recognized:<ref name="Virus Taxonomy 2021">{{cite web|url=https://ictv.global/taxonomy|title=Virus Taxonomy: 2024 Release|website=ictv.global|publisher=International Committee on Taxonomy of Viruses|access-date=9 March 2025}}</ref>

'''Realms''': 
* ''[[Adnaviria]]''
* ''[[Duplodnaviria]]''
* ''[[Monodnaviria]]''
* ''[[Riboviria]]''
* ''[[Ribozyviria]]''
* ''[[Singelaviria]]''
* ''[[Varidnaviria]]''
'''''Incertae sedis'' classes''':
* ''[[Naldaviricetes]]''
'''''Incertae sedis'' families''':
{{div col|colwidth=18em}}
* ''[[Alphasatellitidae]]''
* ''[[Ampullaviridae]]''
* ''[[Avsunviroidae]]''
* ''[[Bartogtaviriformidae]]''
* ''[[Bicaudaviridae]]''
* ''[[Brachygtaviriformidae]]''
* ''[[Clavaviridae]]''
* ''[[Eurekaviridae]]''
* ''[[Fuselloviridae]]''
* ''[[Globuloviridae]]''
* ''[[Guttaviridae]]''
* ''[[Halspiviridae]]''
* ''[[Huangdiviridae]]''
* ''[[Itzamnaviridae]]''
* ''[[Nipumfusiviridae]]''
* ''[[Obscuriviridae]]''
* ''[[Ovaliviridae]]''
* ''[[Plasmaviridae]]''
* ''[[Polydnaviriformidae]]''
* ''[[Portogloboviridae]]''
* ''[[Pospiviroidae]]''
* ''[[Rhodogtaviriformidae]]''
* ''[[Spiraviridae]]''
* ''[[Thaspiviridae]]''
* ''[[Tolecusatellitidae]]''

{{div col end}}

'''''Incertae sedis'' genera''': 
* ''[[Dinodnavirus]]''
* ''[[Rhizidiovirus]]''

===Structure-based virus classification===
{{see also|List of higher virus taxa}}
It has been suggested that similarity in virion assembly and structure observed for certain viral groups infecting hosts from different domains of life (e.g., bacterial tectiviruses and eukaryotic adenoviruses or prokaryotic Caudovirales and eukaryotic herpesviruses) reflects an evolutionary relationship between these viruses.<ref>{{cite journal | vauthors = Bamford DH | title = Do viruses form lineages across different domains of life? | journal = Research in Microbiology | volume = 154 | issue = 4 | pages = 231–6 | date = May 2003 | pmid = 12798226 | doi = 10.1016/S0923-2508(03)00065-2 | doi-access = free }}</ref> Therefore, structural relationship between viruses has been suggested to be used as a basis for defining higher-level taxa – structure-based viral lineages – that could complement the ICTV classification scheme of 2010.<ref>{{cite journal | vauthors = Krupovič M, Bamford DH | title = Order to the viral universe | journal = Journal of Virology | volume = 84 | issue = 24 | pages = 12476–9 | date = December 2010 | pmid = 20926569 | pmc = 3004316 | doi = 10.1128/JVI.01489-10 }}</ref>

The ICTV has gradually added many higher-level taxa using relationships in protein folds. All four realms defined in the 2019 release are defined by the presence of a protein of a certain structural family.<ref>{{cite web|url=https://ictv.global/taxonomy|title=Virus Taxonomy: 2019 Release|date=|website=talk.ictvonline.org|publisher=International Committee on Taxonomy of Viruses|access-date=26 April 2020|quote=}}</ref>