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| __NOTOC__
| | #REDIRECT [[Smallpox virus]] |
| {{Smallpox}}
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| {{CMG}}; {{AE}} {{JS}}
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| ==Overview==
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| [[Smallpox]] is caused by the [[variola]] virus.
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| ==Taxonomy==
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| [[Viruses]]; [[DNA virus|dsDNA]]; [[Poxviridae]]; Chordopoxvirinae; [[Orthopoxvirus]]; Variola vera
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| ==Biology==
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| [[Variola virus]] is a [[orthopoxvirus]], from the family [[Poxviridae]], the largest [[viruses]] to [[infect]] humans. It is a 200-400 nm dsDNA virus, lacking icosahedral symmetry. The other [[viruses]] of the family [[Poxviridae]] include:<ref name="MooreSeward2006">{{cite journal|last1=Moore|first1=Zack S|last2=Seward|first2=Jane F|last3=Lane|first3=J Michael|title=Smallpox|journal=The Lancet|volume=367|issue=9508|year=2006|pages=425–435|issn=01406736|doi=10.1016/S0140-6736(06)68143-9}}</ref>
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| * [[Vaccinia virus]]
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| * [[Molluscum contagiosum virus]]
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| * [[Cowpox virus]]
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| * [[Monkeypox virus]]
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| The [[viral]] structure includes:<ref>{{cite book | last = Fields | first = Bernard | title = Fields virology | publisher = Wolters Kluwer Health/Lippincott Williams & Wilkins | location = Philadelphia | year = 2007 | isbn = 0781760607 }}</ref><ref name="pmid8184534">{{cite journal| author=Massung RF, Liu LI, Qi J, Knight JC, Yuran TE, Kerlavage AR et al.| title=Analysis of the complete genome of smallpox variola major virus strain Bangladesh-1975. | journal=Virology | year= 1994 | volume= 201 | issue= 2 | pages= 215-40 | pmid=8184534 | doi=10.1006/viro.1994.1288 | pmc= |url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=8184534 }} </ref><ref name="pmid8661439">{{cite journal| author=Massung RF, Loparev VN, Knight JC, Totmenin AV, Chizhikov VE, Parsons JM et al.| title=Terminal region sequence variations in variola virus DNA. | journal=Virology | year= 1996 | volume= 221 | issue= 2 |pages= 291-300 | pmid=8661439 | doi=10.1006/viro.1996.0378 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=8661439 }} </ref>
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| * [[Outer membrane]]
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| * 2 lateral bodies
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| * 1 dsDNA molecule in its core containing 186,999 base pairs
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| [[Variola virus]] [[genes]] are similar to the ones of [[vaccinia virus]]. Since there is cross-protection between poxviruses, it was possible to use the second as a [[vaccine]] for [[smallpox virus]].<ref name="ShchelkunovResenchuk1993">{{cite journal|last1=Shchelkunov|first1=Sergei N.|last2=Resenchuk|first2=Sergei M.|last3=Totmenin|first3=Alexei V.|last4=Blinov|first4=Vladimir M.|last5=Marennikova|first5=Svetlana S.|last6=Sandakhchiev|first6=Lev S.|title=Comparison of the genetic maps of variola and vaccinia viruses|journal=FEBS Letters|volume=327|issue=3|year=1993|pages=321–324|issn=00145793|doi=10.1016/0014-5793(93)81013-P}}</ref>
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| There are 2 forms of [[variola virus]]:
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| * Variola major
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| * Variola minor
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| Both [[strains]] of the [[virus]] share a large amount of [[genome]], yet they differ clinically. This leads to the assumption that the difference in [[virulence]] resides in alternate [[gene expression]].<ref name="MooreSeward2006">{{cite journal|last1=Moore|first1=Zack S|last2=Seward|first2=Jane F|last3=Lane|first3=J Michael|title=Smallpox|journal=The Lancet|volume=367|issue=9508|year=2006|pages=425–435|issn=01406736|doi=10.1016/S0140-6736(06)68143-9}}</ref><ref name=WHO>{{cite web | title = Smallpox and its Eradication | url = http://apps.who.int/iris/bitstream/10665/39485/1/9241561106.pdf?ua=1 }}</ref>
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| Poxviruses survive in cold and dry environments being able to survive in the [[aerosol]] form, and are killed by hospital disinfectants and [[UV light]].<ref name="MooreSeward2006">{{cite journal|last1=Moore|first1=Zack S|last2=Seward|first2=Jane F|last3=Lane|first3=J Michael|title=Smallpox|journal=The Lancet|volume=367|issue=9508|year=2006|pages=425–435|issn=01406736|doi=10.1016/S0140-6736(06)68143-9}}</ref><ref name=WHO>{{cite web | title = Smallpox and its Eradication | url = http://apps.who.int/iris/bitstream/10665/39485/1/9241561106.pdf?ua=1 }}</ref><ref name="pmid4371586">{{cite journal| author=Thomas G| title=Air sampling of smallpox virus. | journal=J Hyg (Lond) | year= 1974 | volume= 73 | issue= 1 | pages= 1-7 | pmid=4371586 | doi= | pmc=PMC2130554 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=4371586 }} </ref><ref name="pmid13904777">{{cite journal| author=HARPER GJ| title=Airborne micro-organisms: survival tests with four viruses. | journal=J Hyg (Lond) | year= 1961 | volume= 59 | issue= | pages= 479-86 | pmid=13904777 | doi= | pmc=PMC2134455 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=13904777 }} </ref>
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| Unlike other [[DNA viruses]], poxviruses replicate within the [[cytoplasm]] of the host cell. In order to replicate, poxviruses produce a variety of specialized [[proteins]] not produced by other [[DNA viruses]], the most important of which is a viral-associated DNA-dependent RNA polymerase.
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| ==Origin==
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| The date of the appearance of smallpox is not settled. It most likely evolved from a rodent virus between 68,000 and 16,000 years ago.<ref name="Esposito2006">{{cite journal|last1=Esposito|first1=J. J.|title=Genome Sequence Diversity and Clues to the Evolution of Variola (Smallpox) Virus|journal=Science|volume=313|issue=5788|year=2006|pages=807–812|issn=0036-8075|doi=10.1126/science.1125134}}</ref><ref name="LiCarroll2007">{{cite journal|last1=Li|first1=Y.|last2=Carroll|first2=D. S.|last3=Gardner|first3=S. N.|last4=Walsh|first4=M. C.|last5=Vitalis|first5=E. A.|last6=Damon|first6=I. K.|title=On the origin of smallpox: Correlating variola phylogenics with historical smallpox records|journal=Proceedings of the National Academy of Sciences|volume=104|issue=40|year=2007|pages=15787–15792|issn=0027-8424|doi=10.1073/pnas.0609268104}}</ref> This broad range of dates is due to the different records used to calibrate the molecular clock. It appears that the smallpox virus derived from a remote zoonosis from another animal host, that is today extinct.
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| ==Tropism==
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| Little is known about the mechanism responsible for host species [[tropism]] of [[smallpox virus]]. The [[virus]] is known to bind mammalian cells unspecifically. There appears to be no particular extracellular [[receptors]] involved in [[viral]] internalization and initial [[transcription]]. However, [[intracellular]] availability of [[trans-acting factors]] and [[viral]] capacity to block host [[cell]] s antiviral response, such as the [[interferon]] pathway, are though to be important [[intracellular]] factors determining [[viral tropism]]. The overall [[immune response]] by the host towards the [[virus]] will be the key determinant of the [[outcome]] of the [[infection]] and the potential [[transmission]] to other hosts.<ref name="McFadden2005">{{cite journal|last1=McFadden|first1=Grant|title=Poxvirus tropism|journal=Nature Reviews Microbiology|volume=3|issue=3|year=2005|pages=201–213|issn=1740-1526|doi=10.1038/nrmicro1099}}</ref>
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| ==Natural reservoir==
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| [[Humans]] are the only [[natural reservoir]] of [[smallpox virus]].<ref name=CDC>{{cite web | title = Smallpox disease overview | url = http://www.bt.cdc.gov/agent/smallpox/overview/disease-facts.asp }}</ref>
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| ==References==
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| {{Reflist|2}}
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| [[Category:Needs content]]
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| [[Category:Disease]]
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| [[Category:Infectious disease]]
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| [[Category:Pediatrics]]
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| [[Category:Smallpox]]
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| [[Category:Viral diseases]]
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| [[Category:Poxviruses]]
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| {{WH}}
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| {{WS}}
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