Virus classification
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Viruses can be classified in several ways, such as by their geometry, by whether they have envelopes, by the identity of the host organism they can infect, by mode of transmission, or by the type of disease they cause. The most useful classification is probably by the type of nucleic acid the virus contains and its mode of expression. This classification was proposed by Nobel-prize winner David Baltimore. It should be noted that none of these classifications are expected to be phylogenetic, as viruses may not share a common origin.
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2.1.1 Group I - dsDNA viruses (double stranded DNA) |
Overview
The various forms of viruses arise because one of the two strands of DNA in which all cellular life forms store their genetic information is redundant, so that viruses can have either single-stranded or double-stranded genomes. Furthermore, some viruses store their genome in RNA rather than in DNA form. RNA arises in cells as an intermediate when genes are translated into proteins. RNA genomes of viruses can be encoded in two different directions: Either the genes are stored in the 5'->3' direction (positive or + polarity), analogous to the direction in which genes are represented in mRNA in cells, or the genes are stored in the opposite direction (negative or - polarity).
The taxonomy of viruses is similar to that of cellular organisms:
However, the code of nomenclature regulated by the International Committee on Taxonomy of Viruses differs from the others on several points. Most notably, names of orders and families are italicized, and species names are not binomial - instead, they generally take the form of [Disease] Virus. The recognition of orders is very recent and has been deliberately slow; to date, only three have been named, and most families remain unplaced. Approximately 80 families and 4000 species of virus are known.
Classification by genome type
DNA viruses
Group I - dsDNA viruses (double stranded DNA)
- Order Caudovirales (tailed bacteriophages).
- Family Myoviridae - e.g. Enterobacteria phage T4
- Family Podoviridae
- Family Siphoviridae - e.g. Enterobacteria phage λ
- Unassigned
- Family Ascoviridae
- Family Adenoviridae
- Family Asfiviridae
- Family Baculoviridae
- Family Corticoviridae
- Family Fuselloviridae
- Family Guttaviridae
- Family Herpesviridae - e.g. Human herpseviruses
- Family Iridoviridae
- Family Lipothrixviridae
- Family Nimaviridae
- Family Papillomaviridae
- Family Phycodnaviridae
- Family Plasmaviridae
- Family Polyomaviridae - e.g. Simian virus 40
- Family Poxviridae - e.g. Cowpox virus, Variola virus (smallpox)
- Family Rudiviridae
- Family Tectiviridae
- Unassigned genera
- Mimivirus; type species: Acanthamoeba polyphaga mimivirus
Group II - ssDNA viruses (single stranded DNA)
- Unassigned bacteriophages
- Family Inoviridae
- Family Microviridae
- Unassigned viruses
- Family Geminiviridae
- Family Circoviridae
- Family Nanoviridae
- Family Parvoviridae - e.g. Parvovirus B19 (most depend on coinfection with adenoviruses for growth)
- Unassigned genera
- Anellovirus; type species: Torque teno virus
RNA viruses
Group III - dsRNA viruses (double stranded RNA)
- Family Birnaviridae
- Family Chrysoviridae
- Family Cystoviridae
- Family Hypoviridae
- Family Partitiviridae
- Family Reoviridae - e.g Rotavirus
- Family Totiviridae
- Unassigned genera
- Endornavirus; type species: Vicia faba endornavirus
Group IV - (+)ssRNA viruses (positive single stranded RNA or mRNA like)
- Order Nidovirales ("Nested" Viruses)
- Family Arteriviridae
- Family Coronaviridae - e.g. Coronavirus
- Family Roniviridae
- Unassigned
- Family Astroviridae
- Family Barnaviridae
- Family Bromoviridae
- Family Caliciviridae - e.g. Norwalk virus
- Family Closteroviridae
- Family Comoviridae
- Family Dicistroviridae
- Family Flaviviridae - e.g. Yellow fever virus, West Nile virus, Hepatitis C virus
- Family Flexiviridae
- Family Hepeviridae - e.g. Hepatitis E virus
- Family Leviviridae
- Family Luteoviridae
- Family Marnaviridae
- Family Narnaviridae - naked RNA viruses
- Family Nodaviridae
- Family Picornaviridae - e.g. Poliovirus, Rhinovirus, Hepatitis A virus
- Family Potyviridae
- Family Sequiviridae
- Family Tetraviridae
- Family Togaviridae - e.g. Rubella virus
- Family Tombusviridae
- Family Tymoviridae
- Unassigned genera
- Genus Benyvirus; type species: Beet necrotic yellow vein virus
- Genus Cheravirus; type species: Cherry rasp leaf virus
- Genus Furovirus; type species: Soil-borne wheat mosaic virus
- Genus Hordeivirus; type species: Barley stripe mosaic virus
- Genus Idaeovirus; type species: Raspberry bushy dwarf virus
- Genus Machlomovirus; type species: Maize chlorotic mottle virus
- Genus Ourmiavirus; type species: Ourmia melon virus
- Genus Pecluvirus; type species: Peanut clump virus
- Genus Pomovirus; type species: Potato mop-top virus
- Genus Sadwavirus; type species; Satsuma dwarf virus
- Genus Sobemovirus; type species: Southern bean mosaic virus
- Genus Tobamovirus; type species: Tobacco mosaic virus
- Genus Tobravirus; type species: Tobacco rattle virus
- Genus Umbravirus; type species: Carrot mottle virus
Group V - (-)ssRNA viruses (negative single-stranded RNA)
- Order Mononegavirales (non-segmented negative stranded viruses)
- Family Bornaviridae - Borna disease virus
- Family Filoviridae - Ebola viruses, Marburg virus
- Family Paramyxoviridae - e.g. Measles virus, Mumps virus
- Family Rhabdoviridae - e.g. Rabies virus
- Segmented negative stranded viruses
- Family Arenaviridae
- Family Bunyaviridae - e.g. Hantavirus
- Family Orthomyxoviridae - Influenza viruses
- Unassigned genera:
- Genus Deltavirus; type species: Hepatitis delta virus
- Genus Ophiovirus; type species: Citrus psorosis virus
- Genus Tenuivirus; type species: Rice stripe virus
- Genus Varicosavirus; type species: Lettuce big-vein associated virus
DNA and RNA Reverse Transcribing viruses
Group VI - ssRNA-RT viruses (single stranded RNA)
- Family Metaviridae
- Family Pseudoviridae
- Family Retroviridae - Retroviruses, e.g. HIV 1
Group VII - dsDNA-RT viruses (double stranded DNA)
- Family Hepadnaviridae - e.g. Hepatitis B virus
- Family Caulimoviridae - e.g. Cauliflower mosaic virus
Subviral agents
The following agents are smaller than viruses but have some of their properties.
Viroids
- 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
- Family Avsunviroidae
- Genus Avsunviroid; type species: Avocado sunblotch viroid
- Genus Pelamoviroid; type species: Peach latent mosaic viroid
Satellites
- Satellite viruses
- Single-stranded RNA satellite viruses
- Sugroup 1: Chronic bee-paralysis satellite virus
- Subgroup 2: Tobacco necrosis satellite virus
- Single-stranded RNA satellite viruses
- 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
Prions
- Fungal prions
- Mamalian prions
Other resources
External links
- ICTV Index of Viruses (http://www.ncbi.nlm.nih.gov/ICTVdb/Ictv/index.htm)
- Up-to-date 8th ICTV Index classification (http://www-micro.msb.le.ac.uk/3035/VirusGroups.html)
See also
- Taxonomy
- Scientific classification
- Binomial nomenclature
- Trinomial nomenclature
- WikiSpecies:Virusda:Vira (klassifikation)
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