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Virus classification is the process of naming
virus A virus is a submicroscopic infectious agent In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecu ...

virus
es and placing them into a
taxonomic Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only about biological ...
system similar to the classification systems used for cellular organisms. Viruses are classified by
phenotypic In genetics Genetics is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular inter ...
characteristics, such as
morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology) In archaeology, morphology is the study of the shape of Artifact (archaeology), artefacts and ecofacts. Morphology is a major consid ...

morphology
,
nucleic acid Nucleic acids are biopolymer Biopolymers are natural polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecule ...

nucleic acid
type, mode of replication,
host organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
s, and the type of
disease A disease is a particular abnormal condition that negatively affects the structure A structure is an arrangement and organization of interrelated elements in a material object or system A system is a group of Interaction, interactin ...
they cause. The formal taxonomic classification of viruses is the responsibility of the
International Committee on Taxonomy of Viruses The International Committee on Taxonomy of Viruses (ICTV) authorizes and organizes the Taxonomy (biology), taxonomic classification of and the nomenclatures for viruses. The ICTV has developed a universal taxonomic scheme for viruses, and thus h ...
(ICTV) system, although the
Baltimore classification Baltimore classification is a system used to Virus classification, classify viruses based on their manner of messenger RNA (mRNA) synthesis. By organizing viruses based on their manner of mRNA production, it is possible to study viruses that behav ...

Baltimore classification
system can be used to place viruses into one of seven groups based on their manner of mRNA synthesis. Specific naming conventions and further classification guidelines are set out by the ICTV. A catalogue of all the world's known viruses has been proposed and, in 2013, some preliminary efforts were underway.


Virus species definition

Species form the basis for any biological classification system. Before 1982, it was thought that viruses could not be made to fit
Ernst Mayr Ernst Walter Mayr (; 5 July 1904 – 3 February 2005) was one of the 20th century's leading evolutionary biologists File:Francesco Redi.jpg, Francesco Redi, the founder of biology, is recognized to be one of the greatest biologists of all t ...
's reproductive concept of species, and so were not amenable to such treatment. In 1982, the ICTV started to define a species as "a cluster of strains" with unique identifying qualities. In 1991, the more specific principle that a virus species is a polythetic class of viruses that constitutes a replicating lineage and occupies a particular ecological niche was adopted. In July 2013, the ICTV definition of species changed to state: "A species is a
monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...

monophyletic
group of viruses whose properties can be distinguished from those of other species by multiple criteria." These criteria include the structure of the
capsid A capsid is the protein shell of a virus A virus is a that only inside the living of an . Viruses infect all , from animals and plants to s, including and . Since 's 1892 article describing a non-bacterial infecting tobacco plants ...
, the existence of an envelope, the gene expression program for its proteins, host range,
pathogenicity In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
, and most importantly genetic sequence similarity and phylogenetic relationship. The actual criteria used vary by the taxon, and can be inconsistent (arbitrary similarity thresholds) or unrelated to lineage (geography) at times. The matter is, for many, not yet settled.


ICTV classification

The
International Committee on Taxonomy of Viruses The International Committee on Taxonomy of Viruses (ICTV) authorizes and organizes the Taxonomy (biology), taxonomic classification of and the nomenclatures for viruses. The ICTV has developed a universal taxonomic scheme for viruses, and thus h ...
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 The International Union of Microbiological Societies (IUMS), founded in 1927 as the International Society of Microbiology, is one of 40 member unions and associations of the International Science Council The International Science Council (I ...
with the task of developing, refining, and maintaining a universal virus taxonomy. The system shares many features with the classification system of cellular
organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological ...

organism
s, such as
taxon In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechani ...
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 The ''International Code of Nomenclature for algae, fungi, and plants'' (ICN) is the set of rules and recommendations dealing with the formal botanical name A botanical name is a formal scientific name In taxonomy Taxonomy (general) is ...
and
International Code of Zoological Nomenclature The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention Convention may refer to: * Convention (norm), a custom or tradition, a standard of presentation or conduct ** Treaty, an agreement in international law * C ...
. Viral classification starts at the level of realm and continues as follows, with the taxonomic suffixes in parentheses: :
Realm A realm is a community or territory over which a sovereign Sovereign is a title which can be applied to the highest leader in various categories. The word is borrowed from Old French Old French (, , ; Modern French French ( or ...
(''-viria'') ::Subrealm (''-vira'') :::
Kingdom Kingdom may refer to: Monarchy * A type of monarchy * A realm ruled by: **A king, during the reign of a male monarch **A queen regnant, during the reign of a female monarch Taxonomy * Kingdom (biology), a category in biological taxonomy Arts an ...
(''-virae'') ::::Subkingdom (''-virites'') :::::
Phylum In biology, a phylum (; plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken fr ...
(''-viricota'') ::::::Subphylum (''-viricotina'') :::::::
Class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently f ...
(''-viricetes'') ::::::::Subclass (''-viricetidae'') :::::::::
Order Order, ORDER or Orders may refer to: * Orderliness Orderliness is a quality that is characterized by a person’s interest in keeping their surroundings and themselves well organized, and is associated with other qualities such as cleanliness a ...
(''-virales'') ::::::::::Suborder (''-virineae'') :::::::::::
Family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, typically subject to the same Politic ...
(''-viridae'') ::::::::::::Subfamily (''-virinae'') :::::::::::::
Genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying gr ...
(''-virus'') ::::::::::::::Subgenus (''-virus'') :::::::::::::::
Species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

Species
Unlike the system of
binomial nomenclature In taxonomy Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only ...
adopted in cellular species, there is currently no standardized form for virus species names. At present, the ICTV mandates that a species name must contain as few words as possible while remaining distinct, and must not only contain the word virus and the host name. Species names often take the form of '' iseasevirus'', particularly for higher plants and animals. In 2019, the ICTV published a proposal to adopt a more formalized system of binomial nomenclature for virus species names, to be voted on in 2020. However, some virologists later objected to the potential naming system change, arguing that the debate came while many in the field were preoccupied due to the
COVID-19 pandemic The COVID-19 pandemic is an ongoing global pandemic A pandemic (from , , "all" and , , "local people" the 'crowd') is an of an that has spread across a large region, for instance multiple or worldwide, affecting a substantial numbe ...

COVID-19 pandemic
. As of 2019, all levels of taxa except subrealm, subkingdom, and subclass are used. Four realms, one ''
incertae sedis ' () or ''problematica'' is a term used for a taxonomic Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific ...
'' order, 24 ''incertae sedis'' families, and three ''incertae sedis'' genera are recognized: Realms: ''
Duplodnaviria ''Duplodnaviria'' is a Realm (virology), realm of viruses that includes all double-stranded DNA viruses that Genetic code, encode the HK97 fold major capsid protein. The HK97 fold major capsid protein (HK97 MCP) is the primary component of the v ...
'', ''
Monodnaviria ''Monodnaviria'' is a Realm (virology), realm of viruses that includes all DNA_virus#Group II: ssDNA viruses, single-stranded DNA viruses that Genetic code, encode an HUH-tag, endonuclease of the HUH superfamily that initiates rolling circle repl ...
'', ''
Adnaviria ''Adnaviria'' is a Realm (virology), realm of viruses that includes archaeal viruses that have a filamentous virion (i.e. body) and a linear, double-stranded DNA genome. The genome exists in A-form (A-DNA) and encodes a dimeric major capsid protei ...
'', ''
Ribozyviria ''Ribozyviria'' is a Realm (virology), realm of Satellite (biology), satellite nucleic acids. Established in International Committee on Taxonomy of Viruses, ICTV TaxoProp 2020.012D, the realm is named after the presence of genomic and antigenomic ...
'', ''
Riboviria ''Riboviria'' is a realm A realm is a community or territory over which a sovereign Sovereign is a title which can be applied to the highest leader in various categories. The word is borrowed from Old French ''souverain'', which is ultimat ...
'', and ''
Varidnaviria ''Varidnaviria'' is a realm A realm is a community or territory over which a sovereign Sovereign is a title which can be applied to the highest leader in various categories. The word is borrowed from Old French ''souverain'', which is ult ...
'' ''Incertae sedis'' families: *''
Alphasatellitidae ''Alphasatellites'' are single stranded satellite DNASatellite DNA consists of very large arrays of tandemly repeating, non-coding DNA. Satellite DNA is the main component of functional centromeres, and form the main structural constituent of hete ...
'' *'' Ampullaviridae'' *''
Anelloviridae ''Anelloviridae'' is a Family (biology), family of viruses. They are classified as vertebrate viruses and have a non-enveloped capsid, which is round with isometric, icosahedral symmetry and has a triangulation number of 3. The type species is ' ...
'' *''
Avsunviroidae The ''Avsunviroidae'' are a family of viroids. There are four species in three genera (''Avsunviroid'', ''Elaviroid'' and ''Pelamoviroid''). They consist of RNA genomes between 246–375 nucleotides in length. They are single-stranded covalent ...
'' *''
Baculoviridae ''Baculoviridae'' is a family of viruses. Arthropods, lepidoptera, hymenoptera, and diptera serve as natural hosts. There are currently 84 known Virus classification, species in this family, divided among four genera. Baculoviruses are known to ...
'' *''
Bicaudaviridae ''Bicaudaviridae'' is a family of hyperthermophilic archaeal viruses. Members of the genus ''Acidianus'' serve as natural hosts. There is currently only one genus (''Bicaudavirus'') and one species in this family: the type species ''Acidianus tw ...
'' *'' Clavaviridae'' *'' Finnlakeviridae'' *''
Fuselloviridae ''Fuselloviridae'' is a family of viruses. Sulfolobus species, specifically shibatae, solfataricus, and islandicus, serve as natural hosts. There are two genera and nine species in the family. The ''Fuselloviridae'' are ubiquitous in high-temper ...
'' *''
Globuloviridae ''Globuloviridae'' is a family of hyperthermophilic archaeal viruses. Crenarchaea of the genera Pyrobaculum ''Pyrobaculum'' is a genus (biology), genus of the Thermoproteaceae. Description and significance As its Latin name ''Pyrobaculum' ...
'' *'' Guttaviridae'' *'' Halspiviridae'' *'' Hytrosaviridae'' *'' Nimaviridae'' *''
Nudiviridae This category is for articles about virus families (or redirects to such articles). There should be no subcategories. families In human society, family (from la, familia) is a Social group, group of people related either by consanguinity (by ...
'' *'' Ovaliviridae'' *'''' *''
Polydnaviridae A polydnavirus (PDV) is a member of the family (biology), family ''Polydnaviridae'' of insect viruses. There are two genera in the family: ''Bracovirus'' and ''Ichnovirus''. Polydnaviruses form a symbiotic relationship with parasitoid wasps (ic ...
'' *''
Portogloboviridae ''Portogloboviridae'' is a family (biology), family of DNA viruses that infect archaea. It is a proposed family of the Realm (virology), realm ''Varidnaviria''. Viruses in the family are related to ''Halopanivirales''.The references cited in this ...
'' *''
Pospiviroidae The Pospiviroidae are a family of viroid Viroids are small single-stranded, circular RNA Circular RNA (or circRNA) is a type of single-stranded RNA which, unlike linear RNA, forms a covalently closed continuous loop. In circular RNA, the 3' ...
'' *'' Spiraviridae'' *'' Thaspiviridae'' *'' Tolecusatellitidae'' *'' Tristromaviridae'' ''Incertae sedis'' genera: '' Dinodnavirus'', '' Rhizidiovirus''


Structure-based virus classification

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. 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. 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.


Baltimore classification

Baltimore classification (first defined in 1971) is a classification system that places viruses into one of seven groups depending on a combination of their
nucleic acid Nucleic acids are biopolymer Biopolymers are natural polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecule ...

nucleic acid
(
DNA Deoxyribonucleic acid (; DNA) is a molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically Electricity is the set of physical ...

DNA
or
RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Re ...

RNA
), strandedness (single-stranded or double-stranded),
sense A sense is a biological system used by an organism for sensation, the process of gathering information about the world and responding to Stimulus (physiology), stimuli. (For example, in the human body, the brain receives signals from the senses ...
, and method of
replication Replication may refer to: Science * Replication (scientific method), one of the main principles of the scientific method, a.k.a. reproducibility ** Replication (statistics), the repetition of a test or complete experiment ** Replication crisis * ...

replication
. Named after
David Baltimore David Baltimore (born March 7, 1938) is an American biologist A biologist is a professional who has specialized knowledge in the field of biology, understanding the underlying mechanisms that govern the functioning of biological systems w ...

David Baltimore
, a
Nobel Prize The Nobel Prizes ( ; sv, Nobelpriset ; no, Nobelprisen ) are five separate prizes that, according to Alfred Nobel Alfred Bernhard Nobel ( , ; 21 October 1833 – 10 December 1896) was a Swedish chemist, engineer, inventor, busines ...
-winning biologist, these groups are designated by
Roman numerals Roman numerals are a that originated in and remained the usual way of writing numbers throughout Europe well into the . Numbers in this system are represented by combinations of letters from the . Modern style uses seven symbols, each with a ...
. Other classifications are determined by the disease caused by the virus or its morphology, neither of which are satisfactory due to different viruses either causing the same disease or looking very similar. In addition, viral structures are often difficult to determine under the microscope. Classifying viruses according to their
genome In the fields of molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, M ...

genome
means that those in a given category will all behave in a similar fashion, offering some indication of how to proceed with further research. Viruses can be placed in one of the seven following groups:


DNA viruses

Viruses with a DNA
genome In the fields of molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, M ...

genome
, except for the DNA
reverse transcribing viruses ''Revtraviricetes'' is a class of viruses that contains all viruses that encode a reverse transcriptase. The group includes all retroviruses (ssRNA-RT viruses) and dsDNA-RT viruses. It is the sole class in the phylum ''Artverviricota'', which is th ...
, are members of three of the four recognized viral realms: ''
Duplodnaviria ''Duplodnaviria'' is a Realm (virology), realm of viruses that includes all double-stranded DNA viruses that Genetic code, encode the HK97 fold major capsid protein. The HK97 fold major capsid protein (HK97 MCP) is the primary component of the v ...
'', ''
Monodnaviria ''Monodnaviria'' is a Realm (virology), realm of viruses that includes all DNA_virus#Group II: ssDNA viruses, single-stranded DNA viruses that Genetic code, encode an HUH-tag, endonuclease of the HUH superfamily that initiates rolling circle repl ...
'', and ''
Varidnaviria ''Varidnaviria'' is a realm A realm is a community or territory over which a sovereign Sovereign is a title which can be applied to the highest leader in various categories. The word is borrowed from Old French ''souverain'', which is ult ...
''. But the ''
incertae sedis ' () or ''problematica'' is a term used for a taxonomic Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific ...
'' order '' Ligamenvirales'', and many other ''incertae sedis'' families and genera, are also used to classify DNA viruses. The domains ''Duplodnaviria'' and ''Varidnaviria'' consist of double-stranded DNA viruses; other double-stranded DNA viruses are ''incertae sedis''. The domain ''Monodnaviria'' consists of single-stranded DNA viruses that generally encode a HUH
endonuclease Endonucleases are enzymes that cleave the phosphodiester bond A phosphodiester bond occurs when exactly two of the hydroxyl groups A hydroxy or hydroxyl group is a functional group with the chemical formula -OH and composed of one oxygen atom ...
; other single-stranded DNA viruses are ''incertae sedis''. *Group I: viruses possess double-stranded DNA. Viruses that cause
chickenpox Chickenpox, also known as varicella, is a highly contagious Contagious may refer to: * Contagious disease Literature * Contagious (magazine), a marketing publication * Contagious (novel), ''Contagious'' (novel), a science fiction thriller ...

chickenpox
and
herpes Herpes simplex is a viral infection A viral disease (or viral infection) occurs when an organism's body is invaded by pathogen In biology Biology is the natural science that studies life and living organisms, including their anatomy ...
are found here. *Group II: viruses possess single-stranded DNA.


RNA viruses

All viruses that have an
RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Re ...

RNA
genome In the fields of molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, M ...

genome
, and that encode an
RNA-dependent RNA polymerase RNA-dependent RNA polymerase (RdRp) or RNA replicase is an enzyme Enzymes () are s that act as s (biocatalysts). Catalysts accelerate . The molecules upon which enzymes may act are called , and the enzyme converts the substrates into diff ...
(RdRp), are members of the kingdom ''
Orthornavirae ''Orthornavirae'' is a kingdom of virus A virus is a submicroscopic infectious agent In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, ch ...
'', within the realm ''
Riboviria ''Riboviria'' is a realm A realm is a community or territory over which a sovereign Sovereign is a title which can be applied to the highest leader in various categories. The word is borrowed from Old French ''souverain'', which is ultimat ...
''. *Group III: viruses possess double-stranded RNA genomes, e.g.
rotavirus ''Rotavirus'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), cir ...

rotavirus
. *Group IV: viruses possess positive-sense single-stranded RNA genomes. Many well known viruses are found in this group, including the
picornaviruses Picornaviruses are a group of related Viral envelope, nonenveloped RNA viruses which infect vertebrates including fish, mammals, and birds. They are viruses that represent a large family of small, Positive-sense single-stranded RNA virus, positi ...
(which is a family of viruses that includes well-known viruses like Hepatitis A virus, enteroviruses, rhinoviruses, poliovirus, and foot-and-mouth virus),
SARS Severe acute respiratory syndrome (SARS) is a viral respiratory disease Respiratory diseases, or lung diseases, are pathology, pathological conditions affecting the organs and tissues that make gas exchange difficult in Breathing, air-breathing ...
virus,
hepatitis C Hepatitis C is an infectious disease caused by the hepatitis C virus (HCV) that primarily affects the liver; it is a type of viral hepatitis. During the initial infection people often have mild or no symptoms. Occasionally a fever, dark urine, a ...

hepatitis C
virus,
yellow fever Yellow fever is a viral disease of typically short duration. In most cases, symptoms include fever Fever, also referred to as pyrexia, is defined as having a above the due to an increase in the body's temperature . There is not a singl ...
virus, and
rubella Rubella, also known as German measles or three-day measles, is an infection An infection is the invasion of an organism's body by , their multiplication, and the reaction of tissues to the infectious agents and the s they produce. An inf ...

rubella
virus. *Group V: viruses possess negative-sense single-stranded RNA genomes.
Ebola Ebola, also known as Ebola virus disease (EVD) and Ebola hemorrhagic fever (EHF), is a viral hemorrhagic fever Viral hemorrhagic fevers (VHFs) are a diverse group of animal and human illness A disease is a particular abnormal c ...

Ebola
and
Marburg virus Marburg virus is a Viral hemorrhagic fever, hemorrhagic fever virus of the ''Filoviridae'' family of viruses and a member of the species ''Marburg marburgvirus'', genus ''Marburgvirus''. Marburg virus (MARV) causes Marburg virus disease in human ...

Marburg virus
es are well known members of this group, along with
influenza virus ''Orthomyxoviridae'' (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population ...

influenza virus
,
measles Measles is a highly contagious infectious disease An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction of host (biology), host tissues to ...
,
mumps Mumps is a viral disease A viral disease (or viral infection) occurs when an organism's body is invaded by pathogenic viruses, and infection, infectious virus particles (virions) attach to and enter susceptible cells. Structural characteris ...

mumps
and
rabies Rabies is a viral disease A viral disease (or viral infection) occurs when an organism's body is invaded by pathogenic viruses, and infection, infectious virus particles (virions) attach to and enter susceptible cells. Structural characteri ...
.


Reverse transcribing viruses

All viruses that encode a
reverse transcriptase A reverse transcriptase (RT) is an enzyme Enzymes () are protein Proteins are large s and s that comprise one or more long chains of . Proteins perform a vast array of functions within organisms, including , , , providing and , an ...
(also known as RT or RNA-dependent DNA polymerase) are members of the class '' Revtraviricetes'', within the phylum ''Arterviricota'', kingdom ''Pararnavirae'', and realm ''
Riboviria ''Riboviria'' is a realm A realm is a community or territory over which a sovereign Sovereign is a title which can be applied to the highest leader in various categories. The word is borrowed from Old French ''souverain'', which is ultimat ...
''. The class ''Blubervirales'' contains the single family ''
Hepadnaviridae ''Hepadnaviridae'' is a family of viruses. Humans, apes, and birds serve as natural hosts. There are currently 18 species in this family, divided among 5 genera. Its best-known member is hepatitis B virus. Diseases associated with this family i ...
'' of DNA RT (reverse transcribing) viruses; all other RT viruses are members of the class
Ortervirales ''Ortervirales'' is an order that contains all accepted species of single-stranded RNA viruses that replicate through a DNA intermediate (Group VI) and all accepted species of double-stranded DNA viruses (except ''Hepadnaviridae'') that replicate ...
. *Group VI: viruses possess single-stranded RNA viruses that replicate through a DNA intermediate. The
retrovirus A retrovirus is a type of virus A virus is a submicroscopic infectious agent In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical ...

retrovirus
es are included in this group, of which
HIV The human immunodeficiency viruses (HIV) are two species of ''Lentivirus ''Lentivirus'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, inc ...

HIV
is a member. *Group VII: viruses possess double-stranded DNA genomes and replicate using reverse transcriptase. The
hepatitis B Hepatitis B is an infectious disease An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction of host (biology), host tissues to the infectious a ...
virus can be found in this group.


Historical systems


Holmes classification

Holmes Holmes may refer to: Name * Holmes (surname) * Holmes (given name) * Baron Holmes, noble title created twice in the Peerage of Ireland * Baron Holmes of Richmond, British life peer Places In the United States * Holmes, California, an unincorpo ...
(1948) used a Linnaean taxonomy with
binomial nomenclature In taxonomy Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only ...
to classify viruses into 3 groups under one order, Virales. They are placed as follows: *Group I: ''Bacteriophage, Phaginae'' (attacks bacteria) *Group II: ''Plant virus, Phytophaginae ''(attacks plants) *Group III: ''Animal virus, Zoophaginae'' (attacks animals) The system was not accepted by others due to its neglect of morphological similarities.


Subviral agents

The following infectious agents are smaller than viruses and have only some of their properties.
updated version in sync with current release
Since 2015, the ICTV has allowed them to be classified in a similar way as viruses are.


Viroids and virus-dependent agents


Viroids

*Family ''
Avsunviroidae The ''Avsunviroidae'' are a family of viroids. There are four species in three genera (''Avsunviroid'', ''Elaviroid'' and ''Pelamoviroid''). They consist of RNA genomes between 246–375 nucleotides in length. They are single-stranded covalent ...
'' **Genus ''Avsunviroid''; type species: ''Avocado sunblotch viroid'' **Genus ''Pelamoviroid''; type species: ''Peach latent mosaic viroid'' **Genus ''Elaviroid''; type species: ''Eggplant latent viroid'' *Family ''
Pospiviroidae The Pospiviroidae are a family of viroid Viroids are small single-stranded, circular RNA Circular RNA (or circRNA) is a type of single-stranded RNA which, unlike linear RNA, forms a covalently closed continuous loop. In circular RNA, the 3' ...
'' **Genus ''Pospiviroid''; type species: ''Potato spindle tuber viroid'' **Genus ''Hostuviroid''; type species: ''Hop stunt viroid'' **Genus ''Cocadviroid''; type species: ''Coconut cadang-cadang viroid'' **Genus ''Apscaviroid''; type species: ''Apple scar skin viroid'' **Genus ''Coleviroid''; type species: ''Coleus blumei viroid 1''


Satellites

Satellites depend on co-infection of a host cell with a helper virus for productive multiplication. Their nucleic acids have substantially distinct nucleotide sequences from either their helper virus or host. When a satellite subviral agent encodes the coat protein in which it is encapsulated, it is then called a satellite virus. Satellite-like nucleic acids resemble satellite nucleic acids, in that they replicate with the aid of helper viruses. However they differ in that they can encode functions that can contribute to the success of their helper viruses; while they are sometimes considered to be genomic elements of their helper viruses, they are not always found within their helper viruses. *Satellite viruses **Single-stranded
RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Re ...

RNA
satellite viruses ***(unnamed family) ****''Aumaivirus'' – ''Maize white line mosaic satellite virus'' ****''Papanivirus'' – ''Panicum mosaic satellite virus'' ****''Virtovirus'' – ''Tobacco mosaic satellite virus'' ****''Albetovirus'' – ''Tobacco necrosis satellite virus'' ***Family ''Sarthroviridae'' **** ''Macronovirus'' – ''Macrobrachium satellite virus 1'' (extra small virus) *** (unnamed genus) – ''Nilaparvata lugens commensal X virus'' *** (unnamed genus) – ''Chronic bee-paralysis satellite virus'' ** Double-stranded
DNA Deoxyribonucleic acid (; DNA) is a molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically Electricity is the set of physical ...

DNA
satellite viruses *** Family ''Lavidaviridae'' – Virophages **Single-stranded
DNA Deoxyribonucleic acid (; DNA) is a molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically Electricity is the set of physical ...

DNA
satellite viruses *** Genus ''Dependoparvovirus'' – Adeno-associated virus group *Satellite nucleic acids **Single-stranded satellite DNAs ***Family
Alphasatellitidae ''Alphasatellites'' are single stranded satellite DNASatellite DNA consists of very large arrays of tandemly repeating, non-coding DNA. Satellite DNA is the main component of functional centromeres, and form the main structural constituent of hete ...
(encoding a replication initiator protein) ***Family Tolecusatellitidae (encoding a pathogenicity determinant βC1) **Double-stranded satellite RNAs **Single-stranded satellite RNAs ***Subgroup 1: Large satellite RNAs ***Subgroup 2: Small linear satellite RNAs ***Subgroup 3: Circular satellite RNAs (virusoids) ***Genus ''Deltavirus'' *** Polerovirus-associated RNAs **Satellite-like RNA **Satellite-like DNA


Defective interfering particles

Defective interfering particles are defective viruses that have lost their ability to replicate except in the presence of a helper virus, which is normally the parental virus. They can also interfere with the helper virus. *Defective interfering particles (RNA) *Defective interfering particles (DNA)


See also


Notes


External links


ICTV web site

ICTV International Committee on Taxonomy of Viruses Master Species List 2009 Version 10 (This is version was published on August 24, 2011)



Virus Pathogen Database and Analysis Resource (ViPR)

How are Viruses Classified?
{{DEFAULTSORT:Virus Classification Virus taxonomy, classification Biological classification