Virus Tax Info

Virus Taxonomy Assignments
A more complete description of the process involved in making taxonomic assignments
can be found in the ICTV 9th Report. A summary is provided below.
Viral taxa. The 7th lCTV Report
formalized for the first time the concept of the virus species as the lowest taxon
(group) in a branching hierarchy of viral taxa. As defined therein, “a virus species
is a polythetic class of viruses that constitute a replicating lineage and occupy
a particular ecological niche”. A “polythetic class” is one whose members have several
properties in common, although they do not necessarily all share a single common
defining property. In other words, the members of a virus species are defined collectively
by a consensus group of properties. Virus species thus differ from the higher viral
taxa, which are “universal” classes and as such are defined by properties that are
necessary for membership.

  • Viruses are real physical entities produced by biological evolution and genetics, whereas
    virus species and higher taxa are abstract concepts produced by rational thought and logic. The
    virus/species relationship thus represents the front line of the interface between biology and logic.
  • Viruses (including virus isolates, strains, variants, types, sub-types, serotypes, etc.) should wherever
    possible be assigned as members of the appropriate virus species, although many viruses remain unassigned
    because they are inadequately characterized.
  • All virus species must be represented by at least one virus isolate.
  • Almost all virus species are members of recognized genera. A few species remain unassigned in their families
    although they have been clearly identified as new species.
  • Some genera are members of recognized sub-families.
  • All sub-families and most genera are members of recognized families. Some genera are not yet assigned
    to a family; in the future they may either join an existing family or constitute a new family with other
    unassigned genera.
  • Some families are members of the following recognized orders: Caudovirales, Nidovirales and Mononegavirales.
  • The hierarchy of recognized viral taxa is therefore:

  • Only the aforementioned taxa are recognized by the ICTV. Other groupings (from clade to super-family),
    may communicate useful descriptive information in some circumstances but they have no formally recognized
    taxonomic meaning. Similarly, the term “quasi-species”, although it captures an important concept, has
    no recognized taxonomic meaning.

The creation or elimination, (re)naming, and (re)assignment of a virus species, genus, (sub)family,
or order are all taxonomic acts that require public scrutiny and debate, leading to formal approval by
the full membership of the ICTV. In contrast, the naming of a virus isolate and its assignment to a
pre-existing species are not considered taxonomic acts and therefore do not require formal ICTV approval.
Instead they will typically be accomplished by publication of a paper describing the virus isolate in the
peer-reviewed virology literature.

Descriptions of virus satellites, viroids and the agents of spongiform
encephalopathies (prions) of humans and several animal and fungal species are included.

Virus taxonomy. The advent of nucleotide sequence
determination has revolutionized biology and largely rationalized taxonomy,
including that of viruses. The universal virus taxonomy provides
a classification scheme that is supported by verifiable data and expert
consensus. It is an indispensable framework both for further study of the
currently recognized virus species and for the identification and
characterization of newly emergent viruses, whether they result from natural,
accidental, or deliberate dissemination. The current health of virus taxonomy
is due to the efforts of hundreds of virologists from around the world, but more volunteers
are always needed. Those interested in contributing their expertise are
encouraged to contact the relevant Study Group Chair or any member of the ICTV
Executive Committee.

Number of recognized taxa for each taxonomy release:
(Click on year to view the appropriate taxonomy release)
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