The International Committee on Taxonomy of Viruses (ICTV) authorizes and organizes the taxonomic classification of and the nomenclature for viruses. The ICTV develops a universal taxonomic scheme for viruses, and thus has the means to appropriately describe, name, and classify every virus taxon. The members of the International Committee on Taxonomy of Viruses are considered expert virologists. The ICTV was formed from and is governed by the Virology Division of the International Union of Microbiological Societies. Detailed work, such as identifying new taxa and delimiting the boundaries of species, genera, families, etc. typically is performed by study groups of experts in the families.
History The International Committee on Nomenclature of Viruses (ICNV) was established in 1966, at the International Congress for Microbiology in Moscow, to standardize the naming of virus taxa. The ICVN published its first report in 1971. For viruses infecting vertebrates, the first report included 19 genera, 2 families, and a further 24 unclassified groups. The ICNV was renamed the International Committee on Taxonomy of Viruses in 1974.
Organisational structure The organisation is divided into an executive committee, which includes members and executives with fixed-term elected roles, as well as directly appointed heads of seven subcommittees. Each subcommittee head, in turn, appoints numerous 'study groups', which each consist of one chair and a variable number of members dedicated to the taxonomy of a specific taxon, such as an order or family. This structure may be visualised as follows:
Executive committee President Vice-president Secretaries Business Secretary Proposals Secretary Data Secretary Chairs – positions: 7 (one for each subcommittee) Elected members – positions: 11 Subcommittees Animal DNA Viruses and Retroviruses Subcommittee – study groups: 18 Animal dsRNA and ssRNA- Viruses Subcommittee – study groups: 24 Animal ssRNA+ Viruses Subcommittee – study groups: 16 Bacterial Viruses Subcommittee – study groups: 20 Archaeal Viruses Subcommittee – study groups: 11 Fungal and Protist Viruses Subcommittee – study groups: 12 Plant Viruses Subcommittee – study groups: 22
Objectives The objectives of the International Committee on Taxonomy of Viruses are:
To develop an internationally agreed taxonomy for viruses. To establish internationally agreed names for virus taxa. To communicate the decisions reached concerning the classification and nomenclature of viruses to virologists by holding meetings and publishing reports. To maintain an official index of agreed names of virus taxa. To study the virus effects in modern society and their behaviour.
Principles of nomenclature The ICTV's essential principles of virus nomenclature are:
Stability To avoid or reject the use of names which might cause error or confusion To avoid the unnecessary creation of names The ICTV's universal virus classification system uses a slightly modified version of the standard biological classification system. It only recognises the taxa order, family, subfamily, genus, and species. When it is uncertain how to classify a species into a genus but its classification in a family is clear, it will be classified as an unassigned species of that family. Many taxa remain unranked. There are also, in GenBank sequences assigned to 3,142 "species" which are not accounted for in the ICTV report (due to the way GenBank works, however, the actual number of proper species is probably significantly smaller). The number of unidentified virus sequences is only expected to increase as the rate of virus sequencing increases dramatically. In 2017, the ICTV endorsed a proposal to adapt the classification of viruses in order to keep up better with the growth of available sequences. The ICTV has been strikingly successful in achieving stability, since their inception in 1962. Every genus and family recognized in the 1980s continued to be in use as of 2005, for example.
Naming and changing taxa Proposals for new names, name changes, and the establishment and taxonomic placement of taxa are handled by the executive committee of the ICTV in the form of proposals. All relevant ICTV subcommittees and study groups are consulted prior to a decision being taken. The name of a taxon has no official status until it has been approved by ICTV, and names will only be accepted if they are linked to approved hierarchical taxa. If no suitable name is proposed for a taxon, the taxon may be approved and the name be left undecided until the adoption of an acceptable international name, when one is proposed to and accepted by ICTV. Names must not convey a meaning for the taxon which would seem to either exclude viruses which are rightfully members of that taxon, exclude members which might one day belong to that taxon, or include viruses which are members of different taxa. There is no principle of priority for virology, so that a name in current use cannot be invalidated by claiming priority.
Rules for taxa
Species Since 2020, the Viral Code requires the use of binomial names for new species: a genus followed by a specific epithet. A species name must provide an appropriately unambiguous identification of the species. Before then, a more liberal naming system was in effect: a species name shall consist of as few words as practicable but must not consist only of a host name and the word virus. Numbers, letters, or combinations thereof may be used as species epithets where such numbers and letters are already widely used. However, newly designated serial numbers, letters or combinations thereof are not acceptable alone as species epithets. If a number or letter series is in existence it may be continued.
Genera A virus genus is a group of related species that share some significant properties and often only differ in host range and virulence. A genus name must be a single word ending in the suffix -virus. Approval of a new genus must be accompanied by the approval of a type species.
Subfamilies A subfamily is a group of genera sharing certain common characters. The taxon shall be used only when it is needed to solve a complex hierarchical problem. A subfamily name must be a single word ending in the suffix -virinae.
Families A family is a group of genera, whether or not these are organized into subfamilies, sharing certain common characters with each other. A family name must be a single word ending in the suffix -viridae.
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