The ICTV membership has ratified changes to both the "International Code
of Virus Classification and Nomenclature" as well as the "ICTV Statutes". The changes to the Code take
affect immediately upon ratification, and the updated Code is presented on this page. The changes to the
Statutes require the approval of the Virology Division of the IUMS. If you would like to view the suggested
updates to the Statues, please follow this link to the proposal that defines those updates:
2011.002a-uG.A.v9.statute_and_code_changes.pdf.
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1. Statutory basis for the International Committee on Taxonomy of Viruses (ICTV)
1.1
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.
1.2
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.
(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.
1.3
The Statutes also state that classification and nomenclature will be subject to
Rules set out in an International Code.
Comment: Ratified changes will be published in Virology
Division News in Archives of Virology, and in subsequent ICTV Reports.
2. Principles of Nomenclature
2.1
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.
(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.
2.2
Nomenclature of viruses is independent of other biological nomenclature. Virus
taxon nomenclature is recognized as an exception in the proposed International Code of Bionomenclature
(BioCode).
2.3
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.
2.4
The name of a taxon has no official status until it has been approved by ICTV.
Comment: see section 3.8
3. Rules of Classification and Nomenclature
I - General Rules
The universal scheme
3.1
Virus classification and nomenclature shall be international and shall be
universally applied to all viruses.
3.2
The universal virus classification system shall employ the hierarchical levels of
Order, Family, Subfamily, Genus, and Species.
Comment: It is not obligatory to use all levels of the taxonomic hierarchy. The primary classification
is of viruses into species. Most species are classified into genera and most genera are classified into
families. Species not assigned to a genus will be "unassigned" in a family (see Rule 3.6) and genera not
classified in families have the status of "unassigned" (sometimes referred to as "floating").
Some families are classified into Orders, but often the family is the highest level taxon in use. Also,
families are not necessarily divided into subfamilies. This taxon is to be used only when it is needed to
solve a complex hierarchical problem (see Rule 3.26).
Contrasting examples of full classifications of some negative strand RNA viruses are:- (1) species Mumps virus; genus Rubulavirus; subfamily Paramyxovirinae; family Paramyxoviridae; order Mononegavirales, and (2) species Rice stripe virus; genus Tenuivirus.
Contrasting examples of full classifications of some negative strand RNA viruses are:- (1) species Mumps virus; genus Rubulavirus; subfamily Paramyxovirinae; family Paramyxoviridae; order Mononegavirales, and (2) species Rice stripe virus; genus Tenuivirus.
Scope of the classification
3.3
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.
Comment: A variety of subspecific entities may be identified within a single
virus species. These may be described as viruses (e.g. peanut stripe virus, which is classified in the
species Bean common mosaic virus, genus Potyvirus, family Potyviridae) or as
serotypes, genotypes, strains, variants, isolates etc. Naming of such entities is not the responsibility
of the ICTV but of international specialty groups. It is the responsibility of ICTV Study Groups to
consider how these entities may best be classified into species.
3.4
Artificially created viruses and laboratory hybrid viruses will not be given
taxonomic consideration. Their classification will be the responsibility of acknowledged international
specialist groups.
Limitations
3.5
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.
3.6
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.
Comment: A species can be classified as an unassigned member of a family when
no genus has been devised. For example, Groundnut rosette assistor virus is classified in the family
Luteoviridae but not within any of the current genera of that family.
3.7
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.
Comment: Taxa above the rank of species must be approved before a name is
assigned to them. Proposals for the creation of taxa must be accompanied by proposals for names. A
decision to create a taxon can thus be followed immediately by a decision about the name for the taxon.
Species will be approved together with their names as a single taxonomic act.
The following example is of a proposal concerning an imaginary virus with the vernacular name of porcine gamma virus that is related to another virus, porcine beta virus.
The following example is of a proposal concerning an imaginary virus with the vernacular name of porcine gamma virus that is related to another virus, porcine beta virus.
Proposal 1. Approve Beta gamma virus as a species containing strains known as porcine
gamma virus and porcine beta virus.
Proposal 2. Create a genus to contain Beta gamma virus.
Proposal 3. Name the genus created by Proposal 2, Betavirus.
Proposal 4. Nominate Beta gamma virus as the type species of the genus Betavirus.
Proposal 5. Create a family to contain genus Betavirus and similar genera.
Proposal 6. Name the family created by Proposal 5, Betaviridae.
Proposal 7. Assign species X, Y and Z to genus Betavirus (such a proposal should include a listing of the parameters for discriminating between species in the genus Betavirus).
Proposal 2. Create a genus to contain Beta gamma virus.
Proposal 3. Name the genus created by Proposal 2, Betavirus.
Proposal 4. Nominate Beta gamma virus as the type species of the genus Betavirus.
Proposal 5. Create a family to contain genus Betavirus and similar genera.
Proposal 6. Name the family created by Proposal 5, Betaviridae.
Proposal 7. Assign species X, Y and Z to genus Betavirus (such a proposal should include a listing of the parameters for discriminating between species in the genus Betavirus).
II - Rules about naming Taxa
Status of Names
3.8
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.
Comment: A valid taxon name is one that has been published, one that is
associated with descriptive material, and one that is acceptable in that it conforms to the Rules in the
Code. Accepted names will be kept in an "Index" by the ICTV.
3.9
Existing names of taxa shall be retained whenever feasible.
Comment: A stable nomenclature is one of the principal aims of taxonomy and
therefore changes to names that have been accepted will only be considered if the accepted name conflicts
with the Rules or if a change is necessary to remove ambiguities or confusion.
3.10
The rule of priority in naming taxa shall not be observed.
Comment: The earlier of candidate names for a taxon may be chosen as a convenience
to virologists, but the Rule ensures that it is not possible to invalidate a name in current use by
claiming priority for an older name that has been superseded.
3.11
No person's name shall be used when devising names for new taxa.
Comment: New taxon names shall not be created by adopting a person's name,
by adding a formal ending to a person's name or by using part of a person's name to create a stem
for a name. When existing names of species incorporate a person's name (for example,
Mason-Pfizer monkey virus) continued usage of this name, in agreement with Rule 2.3 and 3.9, is in
general preferable to the creation of a new name.
3.12
Names for taxa shall be easy to use and easy to remember. Euphonious names are
preferred.
Comment: In general, short names are desirable and the number of syllables
should be kept to a minimum.
3.13
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.
Comment: The Rule is intended to make text unambiguous and easy to sort
electronically; its application should often make names more pronounceable, in agreement with Rule 3.12.
3.14
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.
Comment: The name selected for a new taxon should not sound indistinguishable
from the name of another taxon at any rank or from any taxon. For example, the existence of the genus
Iridovirus means that forms of new name such as "irodovirus" or "iridivirus" are unacceptable as they
are too easily confused with an approved name. Confusion can also be between species and genus names as
both end in "virus". Thus, for example, a genus typified by the imaginary species Omega virus would not
be named Omegavirus because species and genus would then be too readily confused.
3.15
Sigla may be accepted as names of taxa, provided that they are meaningful to
virologists in the field, normally as represented by Study Groups.
Comment: Sigla are names comprising letters and/or letter combinations taken
from words in a compound term. The name of the genus Comovirus has the sigla stem "Co-" from cowpea and
"-mo-" from mosaic; the name of the family Reoviridae has the sigla stem "R" from "Respiratory,
"e" from "enteric" and "o" from "orphan".
Decision making
3.16
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.
Comment: When there is more than one candidate name for the same taxon, the
choice of name to be approved will usually be based on the recommendations of a particular Study Group
working on behalf of the ICTV. The Study Group will be expected to consult widely so as to ensure the
acceptability of names, subject to the Rules in the Code. The policy of the ICTV is that, as far as is
possible, decisions on questions of taxonomy and nomenclature should reflect the majority view of the
appropriate virological constituency
3.17
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.
3.18
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
3.19
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.
Comment: Proposals concerning a family containing genera of viruses that infect
diverse types of host (e.g. plants and vertebrates, fungi and plants, and so on) must be considered by
the Subcommittees responsible for viruses of each host type (i.e. Plant viruses, Vertebrate viruses,
and so on). For example, taxonomic proposals concerned with the family Partitiviridae would be
considered by the Fungal Virus Subcommittee and one of its Study Groups but because some genera in the
family contain viruses of plants, proposals affecting the family would also be considered by the
Plant Virus Subcommittee.
III - Rules about Species
Definition of a virus species
3.20
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.
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.
Comment: The criteria by which different species within a genus are
distinguished shall be established by the appropriate Study Group. These criteria may include, but
are not limited to, natural and experimental host range, cell and tissue tropism, pathogenicity,
vector specificity, antigenicity, and the degree of relatedness of their genomes or genes. The criteria
used should be published in the relevant section of the ICTV Report and reviewed periodically by the
Study Group.
Construction of a name
3.21
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".
Comment: Species names normally comprise more than one word (e.g.
Bunyamwera virus).
3.22
A species name must provide an appropriately unambiguous identification of the species.
Comment: Species names should be distinctive. They should not be in a form that
could be easily confused with the names of other taxa.
IV - Rules about Genera
3.23
A genus is a group of species sharing certain common characters.
Comment: It is acceptable for a genus to contain a single species.
3.24
A genus name shall be a single word ending in ...virus.
3.25
Approval of a new genus must be accompanied by the approval of a type species.
V - Rules about Subfamilies
3.26
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.
Comment: It is acceptable for a subfamily to contain a single genus.
3.27
A subfamily name shall be a single word ending in ...virinae.
VI - Rules about Families
3.28
A family is a group of genera (whether or not these are organized into subfamilies)
sharing certain common characters.
Comment: It is acceptable for a family to contain a single genus.
3.29
A family name shall be a single word ending in ...viridae.
VII - Rules about Orders
3.30
An order is a group of families sharing certain common characters.
3.31
An order name shall be a single word ending in ...virales.
VIII - Rules about Sub-viral Agents
Viroids
3.32
Rules concerned with the classification of viruses shall also apply to
the classification of viroids.
3.33
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.
Comment: For example, the species Potato spindle tuber viroid is classified
in the genus Pospiviroid, and the family Pospiviroidae.
Other sub-viral Agents
3.34
Retrotransposons are considered to be viruses in classification and nomenclature
3.35
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
3.36
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.
Comment: See Rule 3.8 for the definition of an "accepted" name.
3.37
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.
Comment: The species names Tobacco mosaic virus and
Murray Valley encephalitis virus are in the correct form and typographical style. Examples of
incorrect forms are Ustilago maydis virus H (not italicized), Murray valley encephalitis virus
(Valley is a proper noun) or tobacco mosaic virus (not capitalized or italicized).
When taxon names are used informally, italics and capital initial letters are not needed. This applies at all taxonomic levels; examples are: (1) "the tobacco mosaic virus polymerase", when describing the properties of the polymerase in members of the species Tobacco mosaic virus and (2) "three pestiviruses", to describe viruses that are members of the genus Pestivirus.
When taxon names are used informally, italics and capital initial letters are not needed. This applies at all taxonomic levels; examples are: (1) "the tobacco mosaic virus polymerase", when describing the properties of the polymerase in members of the species Tobacco mosaic virus and (2) "three pestiviruses", to describe viruses that are members of the genus Pestivirus.
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