Virus classification - wikipedia Virus classification Virus classification is the process of naming viruses and placing them into a taxonomic system. Similar to the classification systems used for cellular organisms, virus classification is the subject of ongoing debate and proposals. This is mainly due to the pseudo-living nature of viruses, which is to say they are non-living particles with some chemical characteristics similar to those of life. As such, they do not fit neatly into the established biological classification system in place for cellular organisms. Viruses are mainly classified by phenotypic characteristics, such as morphology, nucleic acid type, mode of replication, host organisms, and the type of disease they cause. Currently, two main schemes are used for the classification of viruses : the International Committee on Taxonomy of Viruses ( ICTV ) system and Baltimore classification system, which places viruses into one of seven groups. Accompanying this broad method of classification are specific naming conventions and further classification guidelines set out by the ICTV. A catalogue of all the world 's viruses has been proposed ; some related preliminary efforts have been accomplished. Contents 1 Virus species definition 2 ICTV classification 3 Structure - based virus classification 4 Baltimore classification 4.1 DNA viruses 4.2 RNA viruses 4.3 Reverse transcribing viruses 5 Holmes classification 6 LHT System of Virus Classification 7 Subviral agents 7.1 Viroids 7.2 Satellites 7.3 Prions 7.4 Defective interfering particles 8 See also 9 Notes 10 External links Virus species definition Species form the basis for any biological classification system. The ICTV had adopted the principle that a virus species is a polythetic class of viruses that constitutes a replicating lineage and occupies a particular ecological niche. In July 2013, the ICTV definition of species changed to state : `` A species is a monophyletic group of viruses whose properties can be distinguished from those of other species by multiple criteria. '' ICTV classification The International Committee on Taxonomy of Viruses 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 with the task of developing, refining, and maintaining a universal virus taxonomy. The system shares many features with the classification system of cellular organisms, such as taxon structure. However, this system of nomenclature differs from other taxonomic codes on several points. A minor point is that names of orders and families are italicized, unlike in the International Code of Nomenclature for algae, fungi, and plants and International Code of Zoological Nomenclature. Viral classification starts at the level of order and continues as follows, with the taxon suffixes given in italics : Order ( - virales ) Family ( - viridae ) Subfamily ( - virinae ) Genus ( - virus ) Species Species names often take the form of ( Disease ) virus, particularly for higher plants and animals. The establishment of an order is based on the inference that the virus families it contains have most likely evolved from a common ancestor. The majority of virus families remain unplaced. As of 2012, seven orders, 96 families, 22 subfamilies, 420 genera, and 2,618 species of viruses have been defined by the ICTV. The orders are the Caudovirales, Herpesvirales, Ligamenvirales, Mononegavirales, Nidovirales, Picornavirales, and Tymovirales. These orders span viruses with varying host ranges. The Ligamenvirales, infecting archaea, are the most recent addition to the classification system. Caudovirales are tailed dsDNA ( group I ) bacteriophages. Herpesvirales contain large eukaryotic dsDNA viruses. Ligamenvirales contains linear, dsDNA ( group I ) archaean viruses. Mononegavirales include nonsegmented ( - ) strand ssRNA ( Group V ) plant and animal viruses. Nidovirales are composed of ( + ) strand ssRNA ( Group IV ) viruses with vertebrate hosts. Picornavirales contains small ( + ) strand ssRNA viruses that infect a variety of plant, insect and animal hosts. Tymovirales contain monopartite ( + ) ssRNA viruses that infect plants. Other variations occur between the orders : Nidovirales, for example, are isolated for their differentiation in expressing structural and nonstructural proteins separately. 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 existing ICTV classification scheme. Baltimore classification Main articles : Baltimore classification and Virus Information Table The Baltimore Classification of viruses is based on the method of viral mRNA synthesis 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 ( DNA or RNA ), strandedness ( single - stranded or double - stranded ), Sense, and method of replication. Named after David Baltimore, a Nobel Prize - winning biologist, these groups are designated by Roman numerals. 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 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 : I : dsDNA viruses ( e.g. Adenoviruses, Herpesviruses, Poxviruses ) II : ssDNA viruses ( + strand or `` sense '' ) DNA ( e.g. Parvoviruses ) III : dsRNA viruses ( e.g. Reoviruses ) IV : ( + ) ssRNA viruses ( + strand or sense ) RNA ( e.g. Picornaviruses, Togaviruses ) V : ( − ) ssRNA viruses ( − strand or antisense ) RNA ( e.g. Orthomyxoviruses, Rhabdoviruses ) VI : ssRNA - RT viruses ( + strand or sense ) RNA with DNA intermediate in life - cycle ( e.g. Retroviruses ) VII : dsDNA - RT viruses DNA with RNA intermediate in life - cycle ( e.g. Hepadnaviruses ) Visualization of the 7 groups of virus according to the Baltimore Classification DNA viruses For more details on this topic, see DNA virus. Group I : viruses possess double - stranded DNA. Viruses that cause chickenpox and herpes are found here. Group II : viruses possess single - stranded DNA. Virus family Examples ( common names ) Virion naked / enveloped Capsid symmetry Nucleic acid type Group 1. Adenoviridae Adenovirus, infectious canine hepatitis virus Naked Icosahedral ds 2. Papovaviridae Papillomavirus, polyomaviridae, simian vacuolating virus Naked Icosahedral ds circular 3. Parvoviridae Parvovirus B19, canine parvovirus Naked Icosahedral ss II 4. Herpesviridae Herpes simplex virus, varicella - zoster virus, cytomegalovirus, Epstein -- Barr virus Enveloped Icosahedral ds 5. Poxviridae Smallpox virus, cow pox virus, sheep pox virus, orf virus, monkey pox virus, vaccinia virus Complex coats Complex ds 6. Hepadnaviridae Hepatitis B virus Enveloped Icosahedral circular, partially ds VII 7. Anelloviridae Torque teno virus Naked Icosahedral ss circular II RNA viruses For more details on this topic, see RNA virus. Group III : viruses possess double - stranded RNA genomes, e.g. rotavirus. Group IV : viruses possess positive - sense single - stranded RNA genomes. Many well known viruses are found in this group, including the picornaviruses ( which is a family of viruses that includes well - known viruses like Hepatitis A virus, enteroviruses, rhinoviruses, poliovirus, and foot - and - mouth virus ), SARS virus, hepatitis C virus, yellow fever virus, and rubella virus. Group V : viruses possess negative - sense single - stranded RNA genomes. The deadly Ebola and Marburg viruses are well known members of this group, along with influenza virus, measles, mumps and rabies. Virus Family Examples ( common names ) Capsid naked / enveloped Capsid Symmetry Nucleic acid type Group 1. Reoviridae Reovirus, rotavirus Naked Icosahedral ds III 2. Picornaviridae Enterovirus, rhinovirus, hepatovirus, cardiovirus, aphthovirus, poliovirus, parechovirus, erbovirus, kobuvirus, teschovirus, coxsackie Naked Icosahedral ss IV 3. Caliciviridae Norwalk virus Naked Icosahedral ss IV 4. Togaviridae Rubella virus, alphavirus Enveloped Icosahedral ss IV 5. Arenaviridae Lymphocytic choriomeningitis virus Enveloped Complex ss ( - ) V 6. Flaviviridae Dengue virus, hepatitis C virus, yellow fever virus Enveloped Icosahedral ss IV 7. Orthomyxoviridae Influenzavirus A, influenzavirus B, influenzavirus C, isavirus, thogotovirus Enveloped Helical ss ( - ) V 8. Paramyxoviridae Measles virus, mumps virus, respiratory syncytial virus, Rinderpest virus, canine distemper virus Enveloped Helical ss ( - ) V 9. Bunyaviridae California encephalitis virus, hantavirus Enveloped Helical ss ( - ) V 10. Rhabdoviridae Rabies virus Enveloped Helical ss ( - ) V 11. Filoviridae Ebola virus, Marburg virus Enveloped Helical ss ( - ) V 12. Coronaviridae Corona virus Enveloped Helical ss IV 13. Astroviridae Astrovirus Naked Icosahedral ss IV 14. Bornaviridae Borna disease virus Enveloped Helical ss ( - ) V 15. Arteriviridae Arterivirus, equine arteritis virus Enveloped Icosahedral ss IV 16. Hepeviridae Hepatitis E virus Naked Icosahedral ss IV 17. Retroviridae HIV Enveloped Reverse transcribing viruses Group VI : viruses possess single - stranded RNA viruses that replicate through a DNA intermediate. The retroviruses are included in this group, of which HIV is a member. Group VII : viruses possess double - stranded DNA genomes and replicate using reverse transcriptase. The hepatitis B virus can be found in this group. Holmes classification Holmes ( 1948 ) used Carl Linnaeus 's system of binomial nomenclature to classify viruses into 3 groups under one order, Virales. They are placed as follows : Group I : Phaginae ( attacks bacteria ) Group II : Phytophaginae ( attacks plants ) Group III : Zoophaginae ( attacks animals ) LHT system of virus classification The LHT System of Virus Classification is based on chemical and physical characters like nucleic acid ( DNA or RNA ), Symmetry ( Helical or Icosahedral or Complex ), presence of envelope, diameter of capsid, number of capsomers. This classification was approved by the Provisional Committee on Nomenclature of Virus ( PNVC ) of the International Association of Microbiological Societies ( 1962 ). It is as follows : Phylum Vira ( divided into 2 subphyla ) Subphylum Deoxyvira ( DNA viruses ) Class Deoxybinala ( dual symmetry ) Order Urovirales Family Phagoviridae Class Deoxyhelica ( Helical symmetry ) Order Chitovirales Family Poxviridae Class Deoxycubica ( cubical symmetry ) Order Peplovirales Family Herpesviridae ( 162 capsomeres ) Order Haplovirales ( no envelope ) Family Iridoviridae ( 812 capsomeres ) Family Adenoviridae ( 252 capsomeres ) Family Papiloviridae ( 72 capsomeres ) Family Paroviridae ( 32 capsomeres ) Family Microviridae ( 12 capsomeres ) Subphylum Ribovira ( RNA viruses ) Class Ribocubica Order Togovirales Family Arboviridae Order Lymovirales Family Napoviridae Family Reoviridae Class Ribohelica Order Sagovirales Family Stomataviridae Family Paramyxoviridae Family Myxoviridae Order Rhabdovirales Suborder Flexiviridales Family Mesoviridae Family Peptoviridae Suborder Rigidovirales Family Pachyviridae Family Protoviridae Family Polichoviridae Subviral agents The following agents are smaller than viruses but have only some of their properties. Viroids Main article : Viroid Family Avsunviroidae Genus Avsunviroid ; type species : Avocado sunblotch viroid Genus Pelamoviroid ; type species : Peach latent mosaic viroid Genus Elaviroid ; type species : Eggplant latent viroid Family Pospiviroidae 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 Main article : Satellite ( biology ) 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 viruses Single - stranded RNA satellite viruses Subgroup 1 : Chronic bee - paralysis satellite virus Subgroup 2 : Tobacco necrosis satellite virus Double - stranded DNA satellite viruses ( virophages ) Satellite nucleic acids Single - stranded satellite DNAs 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 ) Prions Prions, named for their description as `` proteinaceous and infectious particles '', lack any detectable ( as of 2002 ) nucleic acids or virus - like particles. They resist inactivation procedures that normally affect nucleic acids. Mammalian prions : Agents of spongiform encephalopathies Fungal prions : PSI+ prion of Saccharomyces cerevisiae URE3 prion of Saccharomyces cerevisiae RNQ / PIN+ prion of Saccharomyces cerevisiae Het - s prion of Podospora anserina Defective interfering particles Main article : Defective interfering particle Defective interfering RNA Defective interfering DNA See also Viruses portal Binomial nomenclature Biological classification International Committee on Taxonomy of Viruses List of genera of viruses List of virus species Nomenclature codes Taxonomy Trinomial nomenclature Virology Notes Jump up ^ Zimmer, Carl ( 5 September 2013 ). `` A Catalog for All the World 's Viruses ? ''. New York Times. Retrieved 6 September 2013. Jump up ^ Witzany G ( ed ) ( 2012 ). Viruses : Essential Agents of Life. Springer. ISBN 978 - 94 - 007 - 4898 - 9. Jump up ^ Adams, MJ ; Lefkowitz, EJ ; King, AMQ ; Carstens, EB ( 2013 ). `` Recently agreed changes to the International Code of Virus Classification and Nomenclature ''. Arch Virol. 158 : 2633 -- 9. PMID 23836393. doi : 10.1007 / s00705 - 013 - 1749 - 9. Jump up ^ The Virus Species Concept : Introduction Virus Taxonomy Online : Seventh Report of the International Committee on Taxonomy of Viruses. 2000. Retrieved on 2007 - 07 - 14. ^ Jump up to : ICTV Home Jump up ^ ICTV Virus Taxonomy 2012 Jump up ^ Prangishvili D, Krupovic M ( 2012 ). `` A new proposed taxon for double - stranded DNA viruses, the order `` Ligamenvirales '' ``. Arch Virol. 157 ( 4 ) : 791 -- 795. PMID 22270758. doi : 10.1007 / s00705 - 012 - 1229 - 7. Jump up ^ Bamford DH ( 2003 ). `` Do viruses form lineages across different domains of life ? ''. Res Microbiol. 154 ( 4 ) : 231 -- 236. PMID 12798226. doi : 10.1016 / S0923 - 2508 ( 03 ) 00065 - 2. Jump up ^ Krupovic M, Bamford DH ( 2010 ). `` Order to the Viral Universe '' ( PDF ). J Virol. 84 ( 24 ) : 12476 -- 12479. PMC 3004316. PMID 20926569. doi : 10.1128 / JVI. 01489 - 10. Jump up ^ `` Baltimore Classification of Viruses '' ( Website. ) Molecular Biology Web Book - http://web-books.com/. Retrieved on 2008 - 08 - 18. Jump up ^ Lwoff A, Horne R, Tournier P ( 1962 ). `` A system of viruses ''. Cold Spring Harb. Symp. Quant. Biol. 27 : 51 -- 5. PMID 13931895. doi : 10.1101 / sqb. 1962.027. 001.008. Jump up ^ `` 80.002 Avsunviroidae - ICTVdB Index of Viruses. '' ( Website. ) U.S. National Institutes of Health website. Retrieved on 2007 - 09 - 27. Jump up ^ `` 80.001 Popsiviroidae - ICTVdB Index of Viruses. '' ( Website. ) U.S. National Institutes of Health website. Retrieved on 2007 - 09 - 27. Jump up ^ `` 81. Satellites - ICTVdB Index of Viruses. '' ( Website. ) U.S. National Institutes of Health website. Retrieved on 2007 - 09 - 27. Jump up ^ `` 90. Prions - ICTVdB Index of Viruses. '' ( Website. ) U.S. National Institutes of Health website. Retrieved on 2007 - 09 - 27. External links Wikispecies has information related to : Virus 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 ) The Baltimore Method Virus Pathogen Database and Analysis Resource ( ViPR ) Microbiology : Virus Components Viral envelope Capsid Viral protein Viral life cycle Viral entry Viral replication Viral shedding Virus latency Viroplasm Genetics Reassortment Antigenic shift Antigenic drift Phenotype mixing By host Bacteriophage Virophage Mycovirus Plant virus ( Plant to Human ) Animal virus Human virome Archea virus Amoeba virus Other Viral disease Helper virus Laboratory diagnosis of viral infections Viral load Virus - like particle Viral quantification Antiviral drug Neurotropic virus Oncovirus Social history of viruses Satellite virus Giant viruses Baltimore ( virus classification ) DNA I : dsDNA viruses Caudovirales Myoviridae Podoviridae Siphoviridae Herpesvirales Alloherpesviridae Herpesviridae Malacoherpesviridae Ligamenvirales Lipothrixviridae Rudiviridae Unassigned NLCDV : Ascoviridae Asfarviridae Iridoviridae Marseilleviridae Mimiviridae Phycodnaviridae Poxviridae genera : Dinodnavirus nonenveloped : Adenoviridae Papillomaviridae Papovaviridae ( obsolete ) Polyomaviridae genera : Rhizidiovirus Ampullaviridae Baculoviridae Bicaudaviridae Clavaviridae Corticoviridae Fuselloviridae Globuloviridae Guttaviridae Hytrosaviridae Nimaviridae Nudiviridae Plasmaviridae Polydnaviridae Sphaerolipoviridae Tectiviridae Turriviridae genera : Salterprovirus II : ssDNA viruses Anelloviridae Bidnaviridae Circoviridae Geminiviridae Inoviridae Microviridae Nanoviridae Parvoviridae Spiraviridae genera : Bacilladnavirus RNA III : dsRNA viruses Amalgaviridae Birnaviridae Chrysoviridae Cystoviridae Endornaviridae Hypoviridae Megabirnaviridae Partitiviridae Picobirnaviridae Quadriviridae Reoviridae Totiviridae IV : ( + ) ssRNA viruses ( primarily icosahedral ) Nidovirales Arteriviridae Coronaviridae Mesoniviridae Roniviridae Picornavirales Comoviridae ( obsolete ) Dicistroviridae Iflaviridae Marnaviridae Picornaviridae Secoviridae Sequiviridae ( obsolete ) genera : Bacillarnavirus Labyrnavirus Tymovirales Alphaflexiviridae Betaflexiviridae Gammaflexiviridae Tymoviridae Unassigned Alphatetraviridae Alvernaviridae Astroviridae Barnaviridae Benyviridae Bromoviridae Caliciviridae Carmotetraviridae Closteroviridae Flaviviridae Flexiviridae ( obsolete ) Hepeviridae Leviviridae Luteoviridae Narnaviridae Nodaviridae Permutotetraviridae Potyviridae Tetraviridae ( obsolete ) Togaviridae Tombusviridae Virgaviridae genera : Cilevirus Higrevirus Idaeovirus Ourmiavirus Polemovirus Sobemovirus V : ( - ) ssRNA viruses ( primarily helical ) Mononegavirales Bornaviridae Filoviridae Nyamiviridae Paramyxoviridae Rhabdoviridae Unassigned Arenaviridae Bunyaviridae Ophioviridae Orthomyxoviridae genera : Deltavirus Emaravirus Tenuivirus Varicosavirus RT VI : ssRNA - RT viruses Metaviridae Pseudoviridae Retroviridae VII : dsDNA - RT viruses Caulimoviridae Hepadnaviridae Retrieved from `` https://en.wikipedia.org/w/index.php?title=Virus_classification&oldid=793884798 '' Categories : Virus taxonomy Virology Biological classification Morphology ( biology ) Hidden categories : All articles with unsourced statements Articles with unsourced statements from October 2007 Talk Contents About Wikipedia Български Català Čeština Deutsch Français Galego 한국어 Italiano Latina Magyar Nederlands 日本 語 Polski Português Română Simple English Türkçe 中文 Edit links This page was last edited on 4 August 2017, at 15 : 03. 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Question: where do viruses fit in the current classification system and why
Answer: virus classification is the subject of ongoing debate and proposals