1. Statutory basis for the International Committee on Taxonomy of Viruses (ICTV)
The International Committee on Taxonomy of Viruses (ICTV) is a committee of the
Virology Division of the International Union of Microbiological Societies. ICTV activities are governed
by Statutes agreed with the Virology Division.
The Statutes define the objectives of the ICTV. These are:-
(i) to develop an internationally agreed taxonomy for viruses; (ii) to develop internationally agreed
names for virus taxa; (iii) to communicate taxonomic decisions to the international community of virologists;
(iv) to maintain an Index of agreed names of virus taxa.
The Statutes also state that classification and nomenclature will be subject to
Rules set out in an International Code.
2. Principles of Nomenclature
The essential principles of virus nomenclature are:-
(i) to aim for stability;
(ii) to avoid or reject the use of names which might cause error or confusion; (iii) to avoid the
unnecessary creation of names.
Nomenclature of viruses is independent of other biological nomenclature. Virus
taxon nomenclature is recognized as an exception in the proposed International Code of Bionomenclature
The primary purpose of naming a taxon is to supply a means of referring to the taxon,
rather than to indicate the characters or history of the taxon.
The name of a taxon has no official status until it has been approved by ICTV.
3. Rules of Classification and Nomenclature
I - General Rules
The universal scheme
Virus classification and nomenclature shall be international and shall be
universally applied to all viruses.
The universal virus classification system shall employ the hierarchical levels of
Order, Family, Subfamily, Genus, and Species.
Scope of the classification
The ICTV is not responsible for classification and nomenclature of virus taxa
below the rank of species. The classification and naming of serotypes, genotypes, strains, variants
and isolates of virus species is the responsibility of acknowledged international specialist groups.
Artificially created viruses and laboratory hybrid viruses will not be given
taxonomic consideration. Their classification will be the responsibility of acknowledged international
Taxa will be established only when representative member viruses are sufficiently
well characterized and described in the published literature so as to allow them to be identified
unambiguously and the taxon to be distinguished from other similar taxa.
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.
Names will only be accepted if they are linked to taxa at the hierarchical
levels described in Rule 3.2 and which have been approved by the ICTV.
II - Rules about naming Taxa
Status of Names
Names proposed for taxa are "valid names" if they conform to the Rules set out
in the Code and they pertain to established taxa. Valid names are "accepted names" if they are recorded
as approved International Names in the 8th ICTV Report or have subsequently become "accepted names" by an
ICTV vote of approval for a taxonomic proposal.
Existing names of taxa shall be retained whenever feasible.
The rule of priority in naming taxa shall not be observed.
No person's name shall be used when devising names for new taxa.
Names for taxa shall be easy to use and easy to remember. Euphonious names are
Subscripts, superscripts, oblique bars and non-Latin letters may not be used in
taxon names. Hyphens should not be used when attaching numbers or letters to the end of a series of
species names and should never be used in names of genera, subfamilies, families or orders.
New names shall not duplicate approved names. New names shall be chosen such that
they are not closely similar to names that are in use currently or have been in use in the recent past.
Sigla may be accepted as names of taxa, provided that they are meaningful to
virologists in the field, normally as represented by Study Groups.
In the event of more than one candidate name being proposed, the relevant
Subcommittee will make a recommendation to the Executive Committee of the ICTV, which will then decide
among the candidates as to which to recommend to ICTV for acceptance.
New names shall be selected such that they, or parts of them, do not convey a
meaning for the taxon which would either (1) seem to exclude viruses which lack the character described
by the name but which are members of the taxon being named, or (2) seem to exclude viruses which are as
yet undescribed but which might belong to the taxon being named, or (3) appear to include within the taxon
viruses which are members of different taxa.
New names shall be chosen with due regard to national and/or local sensitivities.
When names are universally used by virologists in published work, these or derivatives shall be the
preferred basis for creating names, irrespective of national origin.
Procedures for naming taxa
All relevant ICTV subcommittees and study groups will be consulted prior to a
decision being taken on any taxonomic proposal submitted to the Executive Committee of the ICTV.
III - Rules about Species
Definition of a virus species
Species shall be created in accordance with the following definition:
A species is the lowest taxonomic level in the hierarchy approved by the ICTV. A species is a monophyletic
group of viruses whose properties can be distinguished from those of other species by multiple criteria.
Construction of a name
A species name shall consist of as few words as practicable but be distinct
from names of other taxa. Species names shall not consist only of a host name and the word "virus".
A species name must provide an appropriately unambiguous identification of the species.
IV - Rules about Genera
A genus is a group of species sharing certain common characters.
A genus name shall be a single word ending in ...virus.
Approval of a new genus must be accompanied by the approval of a type species.
V - Rules about 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 shall be a single word ending in ...virinae.
VI - Rules about Families
A family is a group of genera (whether or not these are organized into subfamilies)
sharing certain common characters.
A family name shall be a single word ending in ...viridae.
VII - Rules about Orders
An order is a group of families sharing certain common characters.
An order name shall be a single word ending in ...virales.
VIII - Rules about Sub-viral Agents
Rules concerned with the classification of viruses shall also apply to
the classification of viroids.
The formal endings for taxa of viroids are the word "viroid" for species, the
suffix "-viroid" for genera, the suffix "-viroinae" for sub-families (should this taxon be needed)
and "-viroidae" for families.
Other sub-viral Agents
Retrotransposons are considered to be viruses in classification and nomenclature
Satellites and prions are not classified as viruses but are assigned an
arbitrary classification as seems useful to workers in the particular fields.
IX - Rules for Orthography
In formal taxonomic usage, the accepted names of virus Orders, Families,
Subfamilies, and Genera are printed in italics and the first letters of the names are capitalized.
Species names are printed in italics and have the first letter of the first word
capitalized. Other words are not capitalized unless they are proper nouns, or parts of proper nouns.