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| __NOTOC__
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| {{Polio}}
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| {{CMG}}; {{AE}} {{JS}}
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| ==Overview==
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| Polio is a highly infectious disease caused by Poliovirus that invades the [[nervous system]]. Poliovirus are small (27–30 nm), nonenveloped viruses with [[capsid]]s enclosing a single-stranded, positive-sense [[RNA]] genome about 7,500 nucleotides long. Person-to-person spread of poliovirus via the fecal-oral route is the most important route of transmission, although the oral-oral route may account for some cases.
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| ==Taxonomy==
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| [[Viruses]]; ssRNA viruses; ssRNA positive-strand viruses, no DNA stage; Picornavirales; [[Picornaviridae]]; [[Enterovirus]]; [[Poliovirus]]<ref name=NCBI>{{cite web | title = Polyomavirus | url = http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=138950 }}</ref>
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| ==Biology==
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| {| style="float: right;"
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| | [[File:Polio EM PHIL 1875 lores.PNG|200px|thumb|none|A Transmission electron microscopy of poliovirus<SMALL> ''Image provided by the CDC [http://phil.cdc.gov/phil/details.asp Centers for Disease Control and Prevention] ''<ref>{{Cite web | title = http://phil.cdc.gov/phil/details.asp | url = http://phil.cdc.gov/phil/details.asp}}</ref></SMALL>]]
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| [[Poliovirus]] is a member of the genus [[enterovirus]], family [[Picornaviridae]]. Enteroviruses are small, nonenveloped, positive stranded RNA viruses. Other members of the family include: [[Rhinovirus]], [[Hepatovirus]], [[Cardiovirus]] and Apthovirus. Poliovirus is a transient inhabitant of the [[gastrointestinal tract]], stable at an acid pH.<ref name=CDC>{{cite web | title = Polyomavirus | url = http://www.cdc.gov/vaccines/pubs/pinkbook/downloads/polio.pdf }}</ref><ref name="pmid15885840">{{cite journal| author=Mueller S, Wimmer E, Cello J| title=Poliovirus and poliomyelitis: a tale of guts, brains, and an accidental event. | journal=Virus Res | year= 2005 | volume= 111 | issue= 2 | pages= 175-93 | pmid=15885840 | doi=10.1016/j.virusres.2005.04.008 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15885840 }} </ref> [[Enteroviruses]] in general do not cause disease, or are responsible for mild symptoms. Disease syndromes resulting from viral spread to other secondary regions are rare. Despite rare, these syndromes may lead to severe disease complications, seldom with fatal outcomes.
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| There are three poliovirus [[serotype]] (P1, P2, and P3) that replicate efficiently in the gastrointestinal tract. There is minimal heterotypic [[immunity]] between the three [[serotype]]s. That is, immunity to one [[serotype]] does not produce significant immunity to the other serotypes. The poliovirus is rapidly inactivated by heat, formaldehyde, chlorine, and ultraviolet light.<ref name=CDC>{{cite web | title = Polyomavirus | url = http://www.cdc.gov/vaccines/pubs/pinkbook/downloads/polio.pdf }}</ref>
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| The characteristics of [[poliovirus]] make it a good model for [[viral]] study, specifically: high viral titers, stable [[capsid]] and ease of purification, along with a low bio-safety requirement.<ref name="pmid15885840">{{cite journal| author=Mueller S, Wimmer E, Cello J| title=Poliovirus and poliomyelitis: a tale of guts, brains, and an accidental event. | journal=Virus Res | year= 2005 | volume= 111 | issue= 2 | pages= 175-93 | pmid=15885840 | doi=10.1016/j.virusres.2005.04.008 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15885840 }} </ref>
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| ==Structure==
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| The genome of poliovirus consists of a single positive-sense RNA molecule, of approximately 7740 nucleotides. At the 5' end of the RNA molecule are coded 88 nucleotides that interact to form a ''clover leaf structure'', which is involved in the replication process.<ref name="pmid15885840">{{cite journal| author=Mueller S, Wimmer E, Cello J| title=Poliovirus and poliomyelitis: a tale of guts, brains, and an accidental event. | journal=Virus Res | year= 2005 | volume= 111 | issue= 2 | pages= 175-93 | pmid=15885840 | doi=10.1016/j.virusres.2005.04.008 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15885840 }} </ref> At the 3' end of the genome is encoded a ''poly Adenine'' sequence, which varies about 60 adenylate residues in length.<ref name="pmid15885840">{{cite journal| author=Mueller S, Wimmer E, Cello J| title=Poliovirus and poliomyelitis: a tale of guts, brains, and an accidental event. | journal=Virus Res | year= 2005 | volume= 111 | issue= 2 | pages= 175-93 | pmid=15885840 | doi=10.1016/j.viruses.2005.04.008 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15885840 }} </ref> The translation of the genome is initiated by the attachment of the host cell's ribosomes to the often called ''internal ribosomal entry site'' (IRES). This is a specific [[RNA]] segment in the 5' end region of the RNA (not translated), where the host cell's translational ribosomes first attach, in order to initiate viral genome replication. The understanding of this mechanism has led to the establishment of a new mechanism of protein synthesis in [[eukaryotes]].<ref name="pmid15885840">{{cite journal| author=Mueller S, Wimmer E, Cello J| title=Poliovirus and poliomyelitis: a tale of guts, brains, and an accidental event. | journal=Virus Res | year= 2005 | volume= 111 | issue= 2 | pages= 175-93 | pmid=15885840 | doi=10.1016/j.virusres.2005.04.008 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15885840 }} </ref>
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| ==Tropism==
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| The cellular receptor for poliovirus was discovered after the transformation of mouse L-cells. These cells were altered with HeLa cell DNA, which led to susceptibility to poliovirus, of previously unsusceptible mice. The cDNA of the cellular receptor for poliovirus was later isolated and named CD155, or PVR. This receptor is a member of the immunoglobulin family, containing 3 Ig domains. CD155 is expressed in the following organs:<ref name="pmid15885840">{{cite journal| author=Mueller S, Wimmer E, Cello J| title=Poliovirus and poliomyelitis: a tale of guts, brains, and an accidental event. | journal=Virus Res | year= 2005 | volume= 111 | issue= 2 | pages= 175-93 | pmid=15885840 | doi=10.1016/j.virusres.2005.04.008 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15885840 }} </ref>
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| * [[Brain]]
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| * [[Spinal cord]]
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| * [[Heart]]
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| * [[Skeletal muscle]]
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| * [[Leukocyte]]s
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| * [[Placenta]]
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| * [[Lung]]
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| * [[Ileum]]
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| * [[Liver]]
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| * [[Kidney]]
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| However, [[viral replication]] does not occur on all [[CD155]]-expressing cells. Possible explanations include:<ref name="pmid15885840">{{cite journal| author=Mueller S, Wimmer E, Cello J| title=Poliovirus and poliomyelitis: a tale of guts, brains, and an accidental event. | journal=Virus Res | year= 2005 | volume= 111 | issue= 2 | pages= 175-93 | pmid=15885840 | doi=10.1016/j.virusres.2005.04.008 | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15885840 }} </ref>
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| * The detection method does not differentiate variants of the receptor. Some variants, despite detected, may not serve as receptor.
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| * Excess secretion isoforms of CD155 may compete for the virus, thereby inactivating the virus.
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| * Other ligands may compete with poliovirus for CD155.
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| * Physical barriers may block poliovirus access to CD155.
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| * Cutoplasm of certain cells may be inadequate for poliovirus replication.
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| Tissues involved in the pathogenesis of the virus, CD155 positive include:
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| * Germinal centers of tonsils
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| * Germinal centers of Peyer’s patches
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| * Epithelium of Peyer's patches
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| * Small intestine enterocytes
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| * Colon enterocytes
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| ==Natural Reservoir==
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| Humans are the only known reservoir of poliovirus, which is transmitted most frequently by persons with inapparent infections. There is no asymptomatic carrier state except in immune deficient persons.
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| <!--
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| Because the poliovirus receptor is only expressed on cells of humans and a few subhuman primate species, there are no known extrahuman reservoirs (7, 8). Following infection, the virus replicates in the gastrointestinal tract and may cause viremia (9, 10). (2)
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| ==References==
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| {{Reflist|2}}
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| [[Category:Needs overview]]
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| [[Category:Disease]]
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| [[Category:Infectious disease]]
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| [[Category:Primary care]]
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| {{WH}}
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| {{WS}}
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