Editing Virus classification (section)

==Baltimore classification==<!-- This section is linked from [[DNA virus]] -->
{{main|Baltimore classification}}
[[File:Baltimore Classification.svg|right|thumb|300px|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 (molecular biology)|sense]], and method of [[Viral replication|replication]].<ref>{{Cite web |date=2017-06-24 |title=9.3B: The Baltimore Virus Classification |url=https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(Boundless)/09:_Viruses/9.03:_Classifying_Viruses/9.3B:_The_Baltimore_Virus_Classification |access-date=2024-09-11 |website=Biology LibreTexts |language=en}}</ref> 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:<ref>{{cite web|title=Baltimore Classification of Viruses|url=http://www.web-books.com/MoBio/Free/Ch1E2.htm|access-date=2023-01-02|website=www.web-books.com}}</ref>

{{Baltimore groups}}
[[File:The Baltimore Classification.gif|left|thumb|800px|Visualization of the 7 groups of virus according to the Baltimore Classification]]
{{clear}}

===DNA viruses===
{{further|DNA virus}}

Viruses with a DNA [[genome]], except for the DNA [[Virus classification#Reverse transcribing viruses|reverse transcribing viruses]], are members of three of the four recognized [[Realm (virology)|viral realms]]: ''[[Duplodnaviria]]'', ''[[Monodnaviria]]'', and ''[[Varidnaviria]]''. But the ''[[incertae sedis]]'' 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-tag|HUH]] [[endonuclease]]; other single-stranded DNA viruses are ''incertae sedis''.<ref name="Virus Taxonomy 2019">{{cite web|url=https://ictv.global/taxonomy|title=Virus Taxonomy: 2019 Release|website=talk.ictvonline.org|publisher=International Committee on Taxonomy of Viruses|access-date=26 April 2020}}</ref>
* '''Group I''': viruses possess double-stranded DNA. Viruses that cause [[chickenpox]] and [[herpes]] are found here.
* '''Group II''': viruses possess single-stranded DNA.

{| class="wikitable"
|+Examples of DNA viruses
|-
! Virus family
! Examples (common names)
! Virion<br /> naked/enveloped
! Capsid<br />symmetry
! Nucleic&nbsp;acid type
! Group
|-
| 1. ''[[Adenoviridae]]''
| [[Canine hepatitis virus]], Some types of the [[common cold]]
| Naked
| Icosahedral
| ds
| I
|-
| 2. ''[[Papovaviridae]]''
| [[JC virus]], [[Human papillomavirus infection|HPV]]
| Naked
| Icosahedral
| ds circular
| I
|-
| 3. ''[[Parvoviridae]]''
| Human [[parvovirus B19]], [[canine parvovirus]]
| Naked
| Icosahedral
| ss
| II
|-
| 4. ''[[Herpesviridae]]''
| [[Herpes simplex virus]], [[varicella-zoster virus]], [[cytomegalovirus]], [[Epstein–Barr virus]]
| [[Viral envelope|Enveloped]]
| Icosahedral
| ds
| I
|-
| 5. ''[[Poxviridae]]''
| [[Smallpox virus]], [[cowpox]], [[myxoma virus]], [[monkeypox]], [[vaccinia virus]]
| Complex coats
| Complex
| ds
| I
|-
| 6. ''[[Anelloviridae]]''
| Torque teno virus
| Naked
| Icosahedral
| ss circular
| II
|-
| {{nowrap|7. ''[[Pleolipoviridae]]''}}
| [[Haloarcula hispanica pleomorphic virus 1|HHPV1]], [[Halorubrum pleomorphic virus 1|HRPV1]]
| Enveloped
|
| ss/ds linear/circular
| I/II
|}

===RNA viruses===
{{further|RNA virus}}

All viruses that have an [[RNA]] [[genome]], and that encode an [[RNA-dependent RNA polymerase]] (RdRp), are members of the kingdom ''[[Orthornavirae]]'', within the realm ''[[Riboviria]]''.<ref name="ictv">{{cite web|title=Virus Taxonomy: 2019 Release|url=https://ictv.global/taxonomy|website=talk.ictvonline.org|publisher=International Committee on Taxonomy of Viruses|access-date=25 April 2020}}</ref>
* '''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), [[Severe Acute Respiratory Syndrome|SARS]] virus, [[hepatitis C]] virus, [[yellow fever]] virus, and [[rubella]] virus.
* '''Group V''': viruses possess negative-sense single-stranded RNA genomes. [[Ebola]] and [[Marburg virus]]es are well known members of this group, along with [[influenza virus]], [[measles]], [[mumps]] and [[rabies]].

{| class="wikitable"
|+Examples of RNA viruses
|-
! Virus Family
! Examples (common names)
! Capsid<br> naked/enveloped
! Capsid<br> Symmetry
! Nucleic&nbsp;acid type
! Group
|-
| 1. ''[[Reoviridae]]''
| [[Reovirus]], [[rotavirus]]
| Naked
| Icosahedral
| ds
| III
|-
| 2. ''[[Picornaviridae]]''
| [[Enterovirus]], [[rhinovirus]], [[hepatovirus]], [[cardiovirus]], [[aphthovirus]], [[poliovirus]], [[parechovirus]], [[erbovirus]], [[kobuvirus]], [[teschovirus]], [[Coxsackievirus|coxsackie]]
| Naked
| Icosahedral
| ss
| IV
|-
| 3. ''[[Caliciviridae]]''
| [[Norovirus|Norwalk virus]]
| Naked
| Icosahedral
| ss
| IV
|-
| 4. ''[[Togaviridae]]''
| [[Eastern equine encephalitis]], [[Chikungunya]]
| [[Viral envelope|Enveloped]]
| Icosahedral
| ss
| IV
|-
| 5. ''[[Arenaviridae]]''
| [[Lymphocytic choriomeningitis virus]], [[Lassa fever]]
| [[Viral envelope|Enveloped]]
| Complex
| ss(−)
| V
|-
| 6. ''[[Flaviviridae]]''
| [[Dengue virus]], [[hepatitis C]] virus, [[yellow fever]] virus, [[Zika virus]]
| [[Viral envelope|Enveloped]]
| Icosahedral
| ss
| IV
|-
| {{nowrap|7. ''[[Orthomyxoviridae]]''}}
| [[Influenzavirus A]], [[influenzavirus B]], [[influenzavirus C]], [[isavirus]], [[thogotovirus]]
| [[Viral envelope|Enveloped]]
| Helical
| ss(−)
| V
|-
| 8. ''[[Paramyxoviridae]]''
| [[Measles virus]], [[mumps virus]], [[respiratory syncytial virus]], [[Rinderpest]] virus, [[canine distemper virus]]
| [[Viral envelope|Enveloped]]
| Helical
| ss(−)
| V
|-
| 9. ''[[Bunyaviridae]]''
| [[California encephalitis virus]], [[Sin nombre virus]]
| [[Viral envelope|Enveloped]]
| Helical
| ss(−)
| V
|-
| 10. ''[[Rhabdoviridae]]''
| [[Rabies virus]], [[Vesicular stomatitis]]
| [[Viral envelope|Enveloped]]
| Helical
| ss(−)
| V
|-
| 11. ''[[Filoviridae]]''
| [[Ebola virus]], [[Marburg virus]]
| [[Viral envelope|Enveloped]]
| Helical
| ss(−)
| V
|-
| 12. ''[[Coronaviridae]]''
|[[Human coronavirus 229E]], [[Human coronavirus NL63]], [[Human coronavirus OC43]], [[Human coronavirus HKU1]], [[Middle East respiratory syndrome-related coronavirus]], [[Severe acute respiratory syndrome coronavirus]], and [[Severe acute respiratory syndrome coronavirus 2]]
| [[Viral envelope|Enveloped]]
| Helical
| ss
| IV
|-
| 13. ''[[Astroviridae]]''
| [[Astrovirus]]
| Naked
| Icosahedral
| ss
| IV
|-
| 14. ''[[Bornaviridae]]''
| [[Borna disease virus]]
| [[Viral envelope|Enveloped]]
| Helical
| ss(−)
| V
|-
| 15. ''[[Arteriviridae]]''
| [[Arterivirus]], [[Equine viral arteritis|equine arteritis virus]]
| [[Viral envelope|Enveloped]]
| Icosahedral
| ss
| IV
|-
| 16. ''[[Hepeviridae]]''
| [[Hepatitis E virus]]
| Naked
| Icosahedral
| ss
| IV
|}

===Reverse transcribing viruses===
All viruses that encode a [[reverse transcriptase]] (also known as RT or RNA-dependent DNA polymerase) are members of the class ''[[Revtraviricetes]]'', within the phylum ''Arterviricota'', kingdom ''Pararnavirae'', and realm ''[[Riboviria]]''. The class ''Blubervirales'' contains the single family ''[[Hepadnaviridae]]'' of DNA RT (reverse transcribing) viruses; all other RT viruses are members of the class [[Ortervirales]].<ref name="Riboviria">{{cite web|title=Proposal: Create a megataxonomic framework, filling all principal taxonomic ranks, for realm Riboviria|url=https://ictv.global/taxonomy/taxondetails?taxnode_id=201907238|last=Koonin EV, Dolja VV, Krupovic M, Varsani A, Wolf YI, Yutin N, Zerbini M, Kuhn JH|website=International Committee on Taxonomy of Viruses (ICTV)|language=en|access-date=2020-05-21}}</ref>
* '''Group VI''': viruses possess single-stranded RNA viruses that replicate through a DNA intermediate. The [[retrovirus]]es 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.
{| class="wikitable"
|+Examples of reverse transcribing viruses
|-
! Virus Family
! Examples (common names)
! Capsid<br> naked/enveloped
! Capsid<br> Symmetry
! Nucleic&nbsp;acid type
! Group
|-
| 1. ''[[Retrovirus|Retroviridae]]''
| [[HIV]]
| [[Viral envelope|Enveloped]]
|
|dimer RNA
|VI
|-
| 2. ''[[Caulimoviridae]]''
| [[Caulimovirus]], {{nowrap|[[Cacao swollen-shoot virus]] (CSSV)}}
| Naked
|
|
|VII
|-
| {{nowrap|3. ''[[Hepadnaviridae]]''}}
| [[Hepatitis B virus]]
| [[Viral envelope|Enveloped]]
| Icosahedral
| circular, partially ds
|VII
|}