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| __NOTOC__
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| {{Polio}}
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| {{CMG}}
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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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| ==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.
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| However, the vast incidence of human infections translates into large numbers of serious disease complications, sometimes with fatal outcome. The pathology of poliovirus is typical for enteroviruses: the three serotypes replicate very efficiently in the GI tract (up to 60 days post infection). Only at a rate of 10−2 (for serotype 1) to 10−3 (for serotypes 2 and 3) does poliovirus cause neurological disease. Thus, the infamous propensity of poliovirus to invade the central nervous system and specifically target motor neurons is rare and accidental and it is neither a prerequisite nor does it present a benefit for its normal life cycle in humans. Poliovirus is a neurotropic virus by mistake; its CNS invasion is mostly a chance event and largely independent of the age, gender, or socioeconomic position of the infected person.
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| There are three poliovirus [[serotype]] (P1, P2, and P3). 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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| [[Poliomyelitis]] is caused by infection with a member of the [[genus]] ''[[enterovirus]]'' known as [[poliovirus]] (PV). This group of [[RNA virus]]es prefers to inhabit the [[gastrointestinal tract]]. PV [[pathogen|infects and causes disease]] in humans alone. Its [[Virus#Structure|structure]] is very simple, composed of a single [[sense (molecular biology)|(+) sense]] [[RNA]] [[genome]] enclosed in a protein shell called a [[capsid]]. In addition to protecting the virus’s genetic material, the capsid proteins enable poliovirus to infect certain types of cells. Three [[serovar|serotype]]s of poliovirus have been identified—poliovirus type 1 (PV1), type 2 (PV2), and type 3 (PV3)—each with a slightly different capsid protein.<ref>{{cite book |author=Katz, Samuel L.; Gershon, Anne A.; Krugman, Saul; Hotez, Peter J. |title=Krugman's infectious diseases of children |publisher=Mosby |location=St. Louis |year=2004 |pages=81–97 |isbn=0-323-01756-8 |oclc= |doi=}}</ref> All three are extremely [[virulence|virulent]] and produce the same disease symptoms. PV1 is the most commonly encountered form, and the one most closely associated with paralysis.
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| Individuals who are exposed to the virus, either through infection or by [[immunization]] with polio vaccine, develop [[immunity (medical)|immunity]]. In immune individuals, [[IgA]] [[antibodies]] against poliovirus are present in the [[tonsil]]s and gastrointestinal tract and are able to block virus replication; [[IgG]] and [[IgM]] antibodies against PV can prevent the spread of the virus to motor neurons of the [[central nervous system]]. Infection or vaccination with one serotype of poliovirus does not provide immunity against the other serotypes, and full immunity requires exposure to each serotype.
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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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| ==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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