virus classification: Information from Answers.com

virus classification
Virus classification involves naming and placingviruses into ataxonomic system. Like the relatively consistent classification systems seen forcellular organisms, virus classification is the subject of ongoing debate and proposals. This is largelydue to thepseudo-living nature of viruses, which are not yet definitively living or non-living.As such, they do not fit neatly into the establishedbiological classificationsystem in place for cellular organisms, such as plants and animals, for several reasons.
Virus classification is based mainly onphenotypic characteristics, includingmorphology,nucleic acid type, mode of replication,host organisms, and the type ofdisease they cause. Acombination of two main schemes is currently in widespread use for the classification of viruses.David Baltimore, aNobel Prize-winning biologist, devised theBaltimore classification system, which places viruses into one of seven groups.These groups are designated byRoman numerals and separate viruses based on their mode ofreplication, and genome type. Accompanying this broad method of classification are specific naming conventions and furtherclassification guidelines set out by theInternational Committeeon Taxonomy of Viruses.
Classification systems
Baltimore classification
Main article:Baltimore classification
Baltimore classification is a classification system which places viruses into one of seven groups depending on a combinationof theirnucleic acid (DNA or RNA), strandedness (single-stranded or double-stranded), andmethod of replication. Other classifications are determined by the disease caused by the virus or its morphology, neither ofwhich are satisfactory due to different viruses either causing the same disease or looking very similar. In addition, viralstructures are often difficult to determine under the microscope. Classifying viruses according to their genome means that thosein 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:
Group I: double-stranded DNA viruses
Group II: single-stranded DNA viruses
Group III: double-stranded RNA viruses
Group IV:positive-sense single-stranded RNA viruses
Group V:negative-sense single-stranded RNA viruses
Group VI:reverse transcribing Diploid single-stranded RNA viruses
Group VII:reverse transcribing Circular double-stranded DNA viruses
ICTV classification
TheInternational Committee on Taxonomy of Virusesdevised and implemented several rules on the naming and classification of viruses early in the 1990‘s. To this day they overseethe naming and placement of viral species into the framework. The system shares many features with the classification system ofcellular organisms, such astaxon structure. Viral classification starts at the level of order andfollows as thus, with the taxon suffixes given in italics:
Order (-virales)Family (-viridae)Subfamily (-virinae)Genus (-virus)Species (-virus)
However, this system of nomenclature differs from other taxonomic codes on several points. A minor point is that names oforders and families are italicized, as in theICBN.Most notably, species names generally take the form of [Disease] Virus. The recognition of orders is very recent and hasbeen deliberately slow; to date, only three have been named, and most families remain unplaced. Approximately 80 families and4000 species of virus are known.
Virus classification
DNA viruses
For more details on this topic, seeDNA virus.
Group I: viruses possess double-stranded DNA and include such virus families asHerpesviridae (examples like HSV1 (oral herpes), HSV2 (genital herpes), VZV (chickenpox), EBV (Epstein-Barr virus), CMV (Cytomegalovirus)),Poxviridae (smallpox) and many tailedbacteriophages. Themimivirus was also placed into this group.
Group II: viruses possess single-stranded DNA and include such virus families asParvoviridae and the importantbacteriophageM13.
Virus Family Virus Genus Virion- naked/ enveloped Capsid Symmetry Type of nucleic acid
1.Adenoviridae Adenovirus Naked Icosahedral ds
2.Papovaviridae Papillomavirus Naked Icosahedral ds circular
3.Parvoviridae B 19 virus Naked Icosahedral ss
4.Herpesviridae Herpes Simplex Virus, Varicella zoster virus, Cytomegalovirus, Epstein Barr virus Enveloped Icosahedral ds
5.Poxviridae Small pox virus, Vaccinia virus Complex coats Complex ds
6.Hepadnaviridae Hepatitis B virus Enveloped Icosahedral ds circular
RNA viruses
For more details on this topic, seeRNA virus.
Group III: viruses possess double-stranded RNA genomes, e.g.rotavirus. These genomes are always segmented.
Group IV: viruses possess positive-sense single-stranded RNA genomes. Many well known viruses are found in this group, including thepicornaviruses (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, andrubella virus.
Group V: viruses possess negative-sense single-stranded RNA genomes. The deadlyEbola andMarburg viruses are well known members of this group, along withinfluenza virus,measles,mumps andrabies.
Virus Family Virus Genus Virion- naked/ enveloped Capsid Symmetry Type of nucleic acid
1.ReoviridaeReovirus,Rotavirus Naked Icosahedral ds
2.PicornaviridaePoliovirus,Rhinovirus,Hepatitis A virus Naked Icosahedral ss
3.CaliciviridaeNorwalk virus,Hepatitis E virus Naked Icosahedral ss
4.TogaviridaeRubella virus Enveloped Icosahedral ss
5.ArenaviridaeLymphocytic choriomeningitis virus Enveloped Complex ss
6.RetroviridaeHIV-1,HIV-2, Human T cell leukemia Enveloped Complex ss
7.FlaviviridaeDengue virus,Hepatitis C virus,Yellow fever virus Enveloped Complex ss
8.OrthomyxoviridaeInfluenza virus Enveloped Helical ss
9.ParamyxoviridaeMeasles virus,Mumps virus,Respiratory syncytial virus Enveloped Helical ss
10.BunyaviridaeCalifornia encephalitis virus,Hantavirus Enveloped Helical ss
11.RhabdoviridaeRabies virus Enveloped Helical ss
12.FiloviridaeEbola virus,Marburg virus Enveloped Helical ss
13.CoronaviridaeCorona virus Enveloped Complex ss
14.Astroviridae Astro virus Naked Icosahedral ss
15.BornaviridaeBorna disease virus Enveloped Helical ss
Reverse transcribing viruses
For more details on this topic, seeReversetranscribing virus.
Group VI: viruses possess single-stranded RNA genomes and replicate usingreverse transcriptase. Theretroviruses are included in this group, of whichHIV is a member.
Group VII: viruses possess double-stranded DNA genomes and replicate usingreverse transcriptase. Thehepatitis B virus can be found in this group.
Subviral agents
The following agents are smaller than viruses but have some of their properties.
Viroids
FamilyPospiviroidae GenusPospiviroid; 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
FamilyAvsunviroidae Genus Avsunviroid; type species:Avocado sunblotch viroid
Genus Pelamoviroid; type species:Peach latent mosaic viroid
Satellites
Satellite viruses Single-stranded RNA satellite viruses Subgroup 1: Chronic bee-paralysis satellite virus
Subgroup 2: Tobacco necrosis satellite virus
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