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Latest revision as of 23:46, 29 July 2020

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]

Overview

Poliovirus is a small, nonenveloped, positive stranded RNA virus, that belongs to the family of Picornaviridae. It is a transient inhabitant of the GI tract, where it replicates, to further infect distant regions, however, poliovirus rarely causes symptoms. Three serotypes of poliovirus, P1, P2 and P3, may be identified. Tissue tropism is dictated by extracellular and intracellular factors. The cellular receptor CD155 is the extracellular receptor for poliovirus. It may be identified in organs, such as the brain, heart, skeletal muscle and liver. Intracellular factors that influence viral replication include: polypyrimidine tract binding protein (PTB), which binds to IRES; the proteolytic processing of poliovirus proteins; and lack of an host factor for viral replication. Humans are the only natural reservoirs for poliovirus.

Taxonomy

Viruses; ssRNA viruses; ssRNA positive-strand viruses, no DNA stage; Picornavirales; Picornaviridae; Enterovirus; Poliovirus^[1]

Biology

A Transmission electron microscopy of poliovirus *Image provided by the CDC Centers for Disease Control and Prevention* ^[2]

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.^[3]^[4] Disease syndromes resulting from viral spread to other secondary organs are rare. Despite this fact, these syndromes lead to severe disease complications, seldom with fatal outcomes.

There are three serotypes of poliovirus (P1, P2, and P3) that replicate efficiently in the gastrointestinal tract. There is minimal heterotypic immunity between the three serotypes. That is, immunity to one serotype does not produce significant immunity to any of the other serotypes. The poliovirus is rapidly inactivated by heat, formaldehyde, chlorine, and ultraviolet light.^[3] The characteristics of poliovirus make it a good model for viral study, namely: high viral titers, stable capsid and ease of purification, along with a low bio-safety requirement.^[4]

Structure

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.^[4] At the 3' end of the genome is encoded a poly Adenine sequence, which varies about 60 adenylate residues in length.^[4] The translation of the genome is initiated by the attachment of 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.^[4]

Tropism

Extracellular Factors

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:^[4]

However, viral replication does not occur on all CD155-expressing cells. Possible explanations include:^[4]

The detection method does not differentiate variants of the receptor. Some variants, despite being detected, may not serve as receptors.
Excess secretion of non-receptor isoforms of CD155 may compete for the virus, thereby inactivating it.
Other ligands may compete with poliovirus for CD155.
Physical barriers may block poliovirus access to CD155.
Cytoplasm of certain cells may be inadequate for poliovirus replication.

CD155 positive tissues involved in the pathogenesis of the virus, include:^[4]

Intracellular Factors

Extracellular viral receptors are not the only determinants of tissue tropism. Genetic properties of the virus, which dictate the ability of poliovirus to replicate within a certain cell environment, are also important contributors to tissue tropism. Cellular host factors also interact with viral RNA, influencing replication. An example is polypyrimidine tract binding protein (PTB), which binds to IRES. This binding initiates a cap-independent translation of the virus, and has also been implicated in alternative splicing mechanisms.^[4] Other factors within the host cell may alter the poliovirus replication cycle:

Proteolytic processing of poliovirus proteins
Lack of an host factors for viral replication
Cessation of protein synthesis within the host cell

Natural Reservoir

Only human cells, and certain primate species, show receptors for poliovirus. Therefore humans are considered the only natural reservoir for poliovirus.^[5]^[6] There is no asymptomatic carrier state, except in the case of immunodeficient patients.^[3]

References

↑ "Poliovirus".
↑ "http://phil.cdc.gov/phil/details.asp". External link in |title= (help)
↑ ^3.0 ^3.1 ^3.2 "Polyomavirus" (PDF).
↑ ^4.0 ^4.1 ^4.2 ^4.3 ^4.4 ^4.5 ^4.6 ^4.7 ^4.8 Mueller S, Wimmer E, Cello J (2005). "Poliovirus and poliomyelitis: a tale of guts, brains, and an accidental event". Virus Res. 111 (2): 175–93. doi:10.1016/j.virusres.2005.04.008. PMID 15885840.
↑ Baury B, Masson D, McDermott BM, Jarry A, Blottière HM, Blanchardie P; et al. (2003). "Identification of secreted CD155 isoforms". Biochem Biophys Res Commun. 309 (1): 175–82. PMID 12943679.
↑ Belnap DM, McDermott BM, Filman DJ, Cheng N, Trus BL, Zuccola HJ; et al. (2000). "Three-dimensional structure of poliovirus receptor bound to poliovirus". Proc Natl Acad Sci U S A. 97 (1): 73–8. PMC 26618. PMID 10618373.

Template:WH Template:WS

[NCBI-1] "Poliovirus".

[2] "http://phil.cdc.gov/phil/details.asp". External link in |title= (help)

[CDC-3] 3.0 ^3.1 ^3.2 "Polyomavirus" (PDF).

[pmid15885840-4] 4.0 ^4.1 ^4.2 ^4.3 ^4.4 ^4.5 ^4.6 ^4.7 ^4.8 Mueller S, Wimmer E, Cello J (2005). "Poliovirus and poliomyelitis: a tale of guts, brains, and an accidental event". Virus Res. 111 (2): 175–93. doi:10.1016/j.virusres.2005.04.008. PMID 15885840.

[pmid12943679-5] Baury B, Masson D, McDermott BM, Jarry A, Blottière HM, Blanchardie P; et al. (2003). "Identification of secreted CD155 isoforms". Biochem Biophys Res Commun. 309 (1): 175–82. PMID 12943679.

[pmid10618373-6] Belnap DM, McDermott BM, Filman DJ, Cheng N, Trus BL, Zuccola HJ; et al. (2000). "Three-dimensional structure of poliovirus receptor bound to poliovirus". Proc Natl Acad Sci U S A. 97 (1): 73–8. PMC 26618. PMID 10618373.

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@@ Line 5: / Line 5: @@
 ==Overview==
-Poliovirus is a small, nonenveloped, positive stranded RNA virus, that belongs to the family of Picornaviridae. It is a transient inhabitant of the GI tract, where it replicates, to further infect distant regions, however, [[poliovirus]] rarely causes symptoms.  Three [[serotype]]s of [[poliovirus]], P1, P2 and P3, may be identified.  Tissue tropism is dictated by extracellualar and intracellular factors. The cellular receptor [[CD155]] is the extracellular receptor for [[poliovirus]].  It may be identified in organs, such as the [[brain]], [[heart]], [[skeletal muscle]] and [[liver]].  Intracellular factors that influence viral [[replication]] include: polypyrimidine tract binding protein (PTB), which binds to IRES; the proteolytic processing of [[poliovirus]] [[proteins]]; and lack of an host factor for [[viral replication]]. Humans are the only [[natural reservoir]]s for [[poliovirus]].
+Poliovirus is a small, nonenveloped, positive stranded [[RNA]] virus, that belongs to the family of [[Picornaviridae]].  It is a transient inhabitant of the GI tract, where it replicates, to further infect distant regions, however, [[poliovirus]] rarely causes [[symptoms]].  Three [[serotype]]s of [[poliovirus]], P1, P2 and P3, may be identified.  Tissue [[tropism]] is dictated by extracellular and intracellular factors. The [[cellular]] receptor [[CD155]] is the extracellular receptor for [[poliovirus]].  It may be identified in organs, such as the [[brain]], [[heart]], [[skeletal muscle]] and [[liver]].  Intracellular factors that influence viral [[replication]] include: polypyrimidine tract binding protein (PTB), which binds to IRES; the proteolytic processing of [[poliovirus]] [[proteins]]; and lack of an host factor for [[viral replication]]. Humans are the only [[natural reservoir]]s for [[poliovirus]].
 ==Taxonomy==
-[[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>
+[[Viruses]]; ssRNA viruses; ssRNA positive-strand viruses, no DNA stage; Picornavirales; [[Picornaviridae]]; [[Enterovirus]]; [[Poliovirus]]<ref name=NCBI>{{cite web | title = Poliovirus | url = http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=138950 }}</ref>
 ==Biology==
@@ Line 15: / Line 15: @@
 |}
-[[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.
+[[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> Disease syndromes resulting from viral spread to other secondary organs are rare. Despite this fact, these syndromes lead to severe disease complications, seldom with fatal outcomes.
-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>
+There are three [[serotype]]s of poliovirus (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 any of the other [[serotype]]s. 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>  The characteristics of [[poliovirus]] make it a good model for [[viral]] study, namely: 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>
-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>
 ==Structure==
-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>
+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 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>
 ==Tropism==
-===Extra-Cellular Tissue Tropism===
+===Extracellular Factors===
 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>
 * [[Brain]]
@@ Line 39: / Line 37: @@
 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>
-* The detection method does not differentiate variants of the [[receptor]]. Some variants, despite detected, may not serve as receptor.
+* The detection method does not differentiate variants of the [[receptor]]. Some variants, despite being detected, may not serve as receptors.
-* Excess [[secretion]] of non-receptor isoforms of [[CD155]] may compete for the virus, thereby inactivating the [[virus]].
+* Excess [[secretion]] of non-receptor isoforms of [[CD155]] may compete for the virus, thereby inactivating it.
 * Other ligands may compete with [[poliovirus]] for [[CD155]].
 * Physical barriers may block [[poliovirus]] access to [[CD155]].
 * [[Cytoplasm]] of certain cells may be inadequate for poliovirus [[viral replication|replication]].
-CD155 positive tissues involved in the [[pathogenesis]] of the [[virus]], 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>
+[[CD155]] positive tissues involved in the [[pathogenesis]] of the [[virus]], 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>
 * Germinal centers of [[tonsils]]
 * Germinal centers of [[Peyer's patches]]
@@ Line 52: / Line 50: @@
 * [[Colon]] [[enterocytes]]
-===Intra-Cellular Tissue Tropism===
+===Intracellular Factors===
-Extra-cellular viral receptors are not the only determinants of tissue tropism. Genetic properties of the virus, which dictate the ability of poliovirus to replicate within a certain cell environment, are also an important contributor for [[tropism]].  [[Cellular]] host factors interact with the viral RNA, influencing [[replication]]. An example is polypyrimidine tract binding protein (PTB), which binds to IRES.  This bound initiates a cap independent [[translation]] of the [[virus]], and has also been implicated in [[alternative splicing]] mechanisms.<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>  Other factors within the host cell may alter the poliovirus replication cycle:
+Extracellular viral receptors are not the only determinants of tissue tropism. Genetic properties of the virus, which dictate the ability of poliovirus to replicate within a certain cell environment, are also important contributors to tissue [[tropism]].  [[Cellular]] host factors also interact with viral [[RNA]], influencing [[replication]]. An example is polypyrimidine tract binding protein (PTB), which binds to IRES.  This binding initiates a cap-independent [[translation]] of the [[virus]], and has also been implicated in [[alternative splicing]] mechanisms.<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>  Other factors within the host cell may alter the poliovirus [[replication]] cycle:
 * Proteolytic processing of poliovirus proteins
-* Lack of an host factor for viral replication
+* Lack of an host factors for viral replication
-* Cease of protein synthesis within the host cell
+* Cessation of protein synthesis within the host cell
 ==Natural Reservoir==
-Only human cells, and certain primate species, show [[receptors]] for [[poliovirus]]. Therefore humans are considered the only [[natural reservoir]] for [[poliovirus]].<ref name="pmid12943679">{{cite journal| author=Baury B, Masson D, McDermott BM, Jarry A, Blottière HM, Blanchardie P et al.| title=Identification of secreted CD155 isoforms. | journal=Biochem Biophys Res Commun | year= 2003 | volume= 309 | issue= 1 | pages= 175-82 | pmid=12943679 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12943679  }} </ref><ref name="pmid10618373">{{cite journal| author=Belnap DM, McDermott BM, Filman DJ, Cheng N, Trus BL, Zuccola HJ et al.| title=Three-dimensional structure of poliovirus receptor bound to poliovirus. | journal=Proc Natl Acad Sci U S A | year= 2000 | volume= 97 | issue= 1 | pages= 73-8 | pmid=10618373 | doi= | pmc=PMC26618 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=10618373  }} </ref>  The is no [[asymptomatic]] carrier state, except in the case of [[immunodeficient]] patients.<ref name=CDC>{{cite web | title = Polyomavirus | url = http://www.cdc.gov/vaccines/pubs/pinkbook/downloads/polio.pdf }}</ref>
+Only human cells, and certain primate species, show [[receptors]] for [[poliovirus]]. Therefore humans are considered the only [[natural reservoir]] for [[poliovirus]].<ref name="pmid12943679">{{cite journal| author=Baury B, Masson D, McDermott BM, Jarry A, Blottière HM, Blanchardie P et al.| title=Identification of secreted CD155 isoforms. | journal=Biochem Biophys Res Commun | year= 2003 | volume= 309 | issue= 1 | pages= 175-82 | pmid=12943679 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12943679  }} </ref><ref name="pmid10618373">{{cite journal| author=Belnap DM, McDermott BM, Filman DJ, Cheng N, Trus BL, Zuccola HJ et al.| title=Three-dimensional structure of poliovirus receptor bound to poliovirus. | journal=Proc Natl Acad Sci U S A | year= 2000 | volume= 97 | issue= 1 | pages= 73-8 | pmid=10618373 | doi= | pmc=PMC26618 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=10618373  }} </ref>  There is no [[asymptomatic]] carrier state, except in the case of immunodeficient patients.<ref name=CDC>{{cite web | title = Polyomavirus | url = http://www.cdc.gov/vaccines/pubs/pinkbook/downloads/polio.pdf }}</ref>
 ==References==
 {{Reflist|2}}
-[[Category:Disease]]
-[[Category:Infectious disease]]
-[[Category:Primary care]]
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+[[Category:Disease]]
-==Origin and serotypes ==
-All three forms of poliovirus are structurally similar to other human enteroviruses, [[coxsackievirus]]es, [[echovirus]]es, and to human [[rhinovirus]]es, which also use immunoglobulin-like molecules to recognize and enter host cells.<ref name=He/> [[Phylogenetic]] analysis of the RNA and protein sequences of poliovirus suggests that PV may have evolved from a C-cluster [[coxsackie A virus]] [[Common descent|ancestor]], arising through a mutation within the capsid.<ref>{{cite journal |author=Jiang P, Faase JA, Toyoda H, ''et al'' |title=Evidence for emergence of diverse polioviruses from C-cluster coxsackie A viruses and implications for global poliovirus eradication |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=104 |issue=22 |pages=9457-62 |year=2007 |pmid=17517601 |doi=10.1073/pnas.0700451104 |url=http://www.pnas.org/cgi/content/full/104/22/9457}}</ref> The distinct [[speciation]] of poliovirus probably occurred as a result of change in cellular receptor specificity from [[intercellular adhesion molecule-1]] (ICAM-1), used by C-cluster coxsackie A viruses, to [[CD155]]; leading to a change in pathogenicity, and allowing the virus to infect nervous tissue.
-==Life cycle==
-[[Image:Poliovirus life cycle.png|thumb|300px|right| The cellular life cycle of poliovirus is initiated (1) by binding to the cell surface receptor CD155. The virion is taken up via endocytosis, and the viral RNA is released (2). Translation of the viral RNA occurs by an IRES-mediated mechanism (3). The polyprotein is cleaved, yielding mature viral proteins (4). The positive-sense RNA serves as template for complementary negative-strand synthesis, producing double-stranded replicative form (RF) RNA(5). Many positive strand RNA copies are produced from the single negative strand (6). The newly synthesized positive-sense RNA molecules can serve as templates for translation of more viral proteins (7) or can be enclosed in a capsid (8), which ultimately generates progeny virions. Lysis of the infected cell results in release of infectious progeny virions (9).<ref name=DeJesus>{{cite journal |author=De Jesus NH |title=Epidemics to eradication: the modern history of poliomyelitis | url= http://www.virologyj.com/content/4/1/70|journal=Virol. J. |volume=4 |issue= |pages=70 |year=2007 |pmid=17623069 |doi=10.1186/1743-422X-4-70}}</ref>]]
-Poliovirus infects human cells by binding to an [[Immunoglobulin|immunoglobulin-like]] receptor, [[CD155]], (also known as the ''poliovirus receptor'' (PVR))<ref name=Mendelsohn>{{cite journal |author=Mendelsohn Cl, Wimmer E, Racaniello VR|title=Cellular receptor for poliovirus: molecular cloning, nucleotide sequence, and expression of a new member of the immunoglobin superfamily |journal=Cell |volume=56 |issue=5 |pages=855-865 |year=1989 |pmid = 2538245}}</ref><ref name=He>{{cite journal |author=He Y, Mueller S, Chipman P, ''et al'' |title=Complexes of poliovirus serotypes with their common cellular receptor, CD155 | url= http://jvi.asm.org/cgi/content/full/77/8/4827?view=long&pmid=12663789| journal=J Virol |volume=77 |issue=8 |pages=4827-35 |year=2003 |pmid = 12663789}}</ref> on the cell surface.<ref name=Dunnebacke>{{cite journal |author=Dunnebacke TH, Levinthal JD, Williams RC|title=Entry and release of poliovirus as observed by electron microscopy of cultured cells |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=4309884| journal=Journal of Virology |volume=4 |issue=4 |pages=505-513 |year=1969 |pmid = 4309884}}</ref> Interaction of poliovirus and CD155 facilitates an irreversible conformational change of the viral particle necessary for viral entry.<ref name= Kaplan>{{cite journal |author=Kaplan G, Freistadat MS, Racaniello VR, |title=Neutralization of poliovirus by cell receptors expressed in insect cells |url= http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=2168959|journal=Journal of Virology |volume=60 |issue=10 |pages=4697-4702 |year=1990 |pmid = 2168959}}</ref><ref name= Gomez>{{cite journal |author=Gomez Yafal A, Kaplan G, Racaniello VR, Hogle, JM |title=Characterization of poliovirus conformational alteration mediated by soluble cell receptors |journal=Virology |volume=197 |issue=1 |pages=501-505 |year=1993 |pmid = 8212594}}</ref> The precise mechanism poliovirus uses to enter the [[Host (biology)|host]] cell has not been firmly established.<ref name=Baron>{{cite book |  title = Picornaviruses: The Enteroviruses: Polioviruses ''in:'' Baron's Medical Microbiology ''(Baron S ''et al'', eds.)| edition = 4th ed. | publisher = Univ of Texas Medical Branch | year = 1996 | url= http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.2862 | isbn = 0-9631172-1-1 }}</ref>  Attached to the host [[cell membrane]], entry of the viral nucleic acid was thought to occur one of two ways: via the formation of a [[pore]] in the plasma membrane through which the RNA is then “injected” into the host cell [[cytoplasm]], or that the virus is taken up by [[receptor-mediated endocytosis]].<ref name= Mueller>{{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 |volume=111 |issue=2 |pages=175-93 |year=2005 |pmid = 15885840}}</ref>  Recent experimental evidence supports the latter hypothesis and suggests that poliovirus binds to CD155 and is taken up via endocytosis. Immediately after internalization of the particle, the viral RNA is released.<ref name= Brandenburg>{{cite journal |author=Brandenburg B, Lee LY, Lakadamyali M, Rust MJ, Zhuang X, Hogle JM, |title=Imaging poliovirus entry in live cells |url= http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0050183&ct=1 |journal=PLOS Biology |volume=5 |issue=7 |pages=e183 |year=2007 |pmid = 17622193}}</ref>  However, any mechanism by which poliovirus enters the cell is very inefficient; as an infection is initiated only about 1% of the time.<ref name= Chan>Charles Chan and Roberto Neisa. [http://www.brown.edu/Courses/Bio_160/Projects2000/Polio/TableofContents.html "Poliomyelitis".] Brown University.</ref>
-Poliovirus is a positive stranded [[RNA virus]]. Thus the genome enclosed within the viral particle can be used as [[messenger RNA]] and immediately [[Translation (biology)|translated]] by the host cell. Upon entry the virus hijacks the cell's translation machinery; causing inhibition of cellular protein synthesis in favor of virus–specific protein production. Unlike most cellular mRNAs the 5' end of poliovirus RNA is extremely long—over 700 nucleotides—and is highly structured. It is this region of the viral genome which directs translation of the viral RNA, and alterations of this region prevent viral protein production. Ultimately it was demonstrated that translation of poliovirus RNA occurs via an [[internal ribosome entry site]] (IRES).<ref name= Chen>{{cite journal |author=Chen CY, Sarnow P |title=Initiation of protein synthesis by the eukaryotic translational apparatus on circular RNAs |journal=Science |volume=268 |issue=5209 |pages=415-417 |year=1995 |pmid = 7536344}}</ref><ref name= Pelletier>{{cite journal |author=Pelletier J, Sonenberg N |title=Internal initiation of translation of eukaryotic mRNA directed by a sequence derived from poliovirus RNA |journal=Nature |volume=334 |issue=6180 |pages=320-325 |year=1988 |pmid = 2839775}}</ref><ref name= Jang>{{cite journal |author=Jang SK, Krausslich HG, Nicklin MJ, Duke GM, Palmenberg AC, Wimmer E |title=A segment of the 5' nontranslated region of encephalomyocarditis virus RNA directs internal entry of ribosome during in vitro translation |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=2839690 |journal=Journal of Virology |volume=62 |issue=8 |pages=2636-2643 |year=1988 |pmid = 2839690}}</ref> Poliovirus mRNA is translated as one long [[polypeptide]].
-This polypeptide is then cleaved into approximately 10 individual viral proteins, including:<ref name = Goodsell /><ref name= Chan/>
-[[Image:Poliovirus genome.png|thumb|left|300px|The genomic structure of poliovirus type 1<ref name=DeJesus/> (see text or reference for further details).]]
-*''3D<sup>pol</sup>'', an [[RNA dependent RNA polymerase]].
-*''2A<sup>pro</sup>'' and ''3C<sup>pro</sup>/3CD<sup>pro</sup>'', [[protease]]s which cleave the viral polypeptide.
-*''[[VPg]]'' (3B), a small protein that binds viral RNA and is necessary for synthesis of viral positive and negative strand RNA.
-*''2BC, 2B, 2C, 3AB, 3A, 3B'' proteins which comprise the protein complex needed for virus replication.
-*''VP0, VP1, VP2, VP3, VP4'' proteins of the viral capsid.
-The assembly of new virus particles, (i.e. the packaging of progeny genome into a capsid which can survive outside the host cell) is poorly understood.<ref name= Mueller/> Fully assembled poliovirus leaves the confines of its host cell 4 to 6 hours following initiation of infection in cultured mammalian cells.<ref name=Kew_2005>{{cite journal |author=Kew O, Sutter R, de Gourville E, Dowdle W, Pallansch M |title=Vaccine-derived polioviruses and the endgame strategy for global polio eradication |journal=Annu Rev Microbiol |volume=59 |issue= |pages=587-635 |year=2005 |pmid=16153180}}</ref> The mechanism of viral release from the cell is unclear,<ref name = Hogle/> but each dying cell can release between 10,000 and 100,000 polio [[virions]].<ref name=Kew_2005/>
-==Pathogenesis==
-[[Image:Polio EM PHIL 1875 lores.PNG|thumb|[[Electron micrograph]] of poliovirus.]]
-The primary determinant of infection for any virus is its ability to enter a cell and produce additional infectious particles. The presence of CD155 is thought to define the animals and tissues that can be infected by poliovirus. CD155 is found only on the cells of humans, higher [[primates]], and [[Old World monkey]]s. Poliovirus is however strictly a human pathogen, and does not naturally infect any other species (although [[chimpanzee]]s and Old World monkeys can be experimentally infected).<ref>{{cite journal |author=Mueller S, Wimmer E |title=Recruitment of nectin-3 to cell-cell junctions through trans-heterophilic interaction with CD155, a vitronectin and poliovirus receptor that localizes to alpha(v)beta3 integrin-containing membrane microdomains | url=http://www.jbc.org/cgi/content/full/278/33/31251| journal=J Biol Chem |volume=278 |issue=33 |pages=31251-60 |year=2003 |pmid=12759359}}</ref>
-Poliovirus is an enterovirus. Infection occurs via the [[fecal-oral route]]; meaning that one ingests the virus and it is within the [[alimentary tract]] that virus replication occurs.<ref name=Bodian_1965>{{cite book |author = Bodian D and Horstmann DH |title=Polioviruse |publisher=Lippincott |location=Philadelphia, Penn |year=1969 |pages= 430-473}}</ref>  Virus is shed in the feces of infected individuals. In 95% of cases only a primary, transient presence of the virus in the bloodstream occurs (called a [[viremia]]) and the poliovirus infection is [[asymptomatic]]. In about 5% of cases, the virus spreads, and replicates in other sites such as [[brown fat]], the [[reticuloendothelial]] tissues, and [[muscle]]. This sustained replication causes a secondary viremia, and leads to the development of minor symptoms such as fever, headache and sore throat.<ref>{{cite journal |author=Sabin A |title=Pathogenesis of poliomyelitis; reappraisal in the light of new data |journal=Science |volume=123 |issue=3209 |pages=1151-7 |year=1956 |pmid=13337331}}</ref> Paraltyic poliomyletis occurs in less than 1% of poliovirus infections. Paralyitic disease occurs when the virus enters the [[central nervous system]] (CNS) and replicates in [[motor neuron]]s within the [[spinal cord]], [[brain stem]], or [[motor cortex]], resulting in the selective destruction of motor neurons; leading to either temporary or permanent [[paralysis]] and, in rare cases, to [[respiratory arrest]] and death. In many respects this [[neurological]] phase of infection is thought to be an accidental diversion of the normal [[gastrointestinal]] infection.<ref name= Mueller/>
-The mechanisms by which poliovirus enters the CNS are poorly understood.  Three theories have been suggested to explain its entry, which are not mutually exclusive, and require that the virus be present in the blood (viremia).  One theory is that virus passes directly from the [[blood]] into the central nervous system by crossing the [[blood brain barrier]], independent of CD155.<ref>{{cite journal |author=Yang W, Terasaki T, Shiroki K, ''et al''|title=Efficient delivery of circulating poliovirus to the central nervous system independently of poliovirus receptor |journal=Virology |volume=229 |issue=2 |pages=421-8 |year=1997 |pmid=9126254 |issn=}}</ref> A second hypothesis suggests that the virus is transported from the muscle to the spinal cord through nerve pathways by [[retrograde]] [[axon]]al transport.<ref>{{cite journal |author=Ohka S. Yang WX, Terada E, Iwasaki K, Nomot A  |title=Retrograde transport of intact poliovirus through the axon via the first transport system |journal=Virology |volume=250 |issue=1 |pages=67-75 |year=1998 |pmid=9770421 |issn=}}</ref><ref>{{cite journal |author=Ren R, Racaniello V |title=Poliovirus spreads from muscle to the central nervous system by neural pathways |journal=J Infect Dis |volume=166 |issue=4 |pages=747-52 |year=1992 |pmid=1326581 |issn=}}</ref> A third hypotheis is that the virus is imported into the CNS by infected [[monocyte]]s or [[macrophage]]s.<ref name=DeJesus/>
-Poliomyelitis is a disease of central nervous system. However, CD155 is believed to be present on the surface of most, if not all, human cells and does not explain why poliovirus preferentially infects certain tissues, suggesting that tissue [[tropism]] is determined after infection. Recent work has suggested that the [[Interferon type I|type I interferon]] response (specifically that of interferon alpha and beta) is an important factor that defines which types of cells are infected by poliovirus.<ref>{{cite journal |author=Ida-Hosonuma M, Iwasaki T, Yoshikawa T, Nagata N, Sato Y, Sata T, Yoneyama M, Fujita T, Taya C, Yonekawa H, Koike S |title=The alpha/beta interferon response controls tissue tropism and pathogencicity of poliovirus |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=15767446 |journal=Journal of Virology |volume=79 |issue=7 |pages=4460-4469 |year=2005 |pmid=15767446}}</ref> In mice expressing CD155 but lacking the type I interferon receptor, poliovirus not only replicates in tissues it normally would not, but these mice are also able to be infected orally with the virus.<ref>{{cite journal |author=Ohka S, Igarashi H, Sakai M, Koike S, Nochi T, Kiyono A, Nomoto A |title=Esstablishment of a poliovirus oral infection system in human poliovirus receptor-expressing transgenic mice that are deficient in alpha/beta interferon receptor  |journal=Journal of Virology |volume=81 |issue=15 |pages=7902-7912 |year=2007 |pmid=17507470}}</ref>
-== Immune system avoidance ==
-Poliovirus uses two key mechanisms to evade the [[immune system]]. First, it is capable of surviving the highly [[pH|acidic]] conditions of the [[gastrointestinal tract]], allowing the virus to infect the host and spread throughout the body via the [[lymphatic system]].<ref name= Goodsell/>  Second, because it can replicate very rapidly - the virus overwhelms the host organs before an immune response can be mounted.<ref name= Racaniello>{{cite journal |author=Racaniello V |title=One hundred years of poliovirus pathogenesis |journal=Virology |volume=344 |issue=1 |pages=9-16 |year=2006 |pmid = 16364730}}</ref>
-Individuals who are exposed to poliovirus, either through infection or by [[immunization]] with [[polio vaccine]], develop [[immunity (medical)|immunity]].  In immune individuals, [[antibodies]] against poliovirus are present in the [[tonsil]]s and gastrointestinal tract (specifically [[IgA]] antibodies) and are able to block poliovirus replication; [[IgG]] and [[IgM]] antibodies against poliovirus can prevent the spread of the virus to motor neurons of the central nervous system.<ref name=Kew_2005/> Infection with one serotype of poliovirus does not provide immunity against the other serotypes, however second attacks within the same individual are extremely rare.
-== PVR transgenic mouse ==
-Although humans are the only known natural hosts of poliovirus, monkeys can be experimentally infected and they have long been used to study poliovirus. In 1990-91, a small animal model of poliomyelitis was developed by two laboratories.  Mice were [[Genetic engineering|engineered]] to express a human receptor to poliovirus (hPVR).<ref name="pmid2170026">{{cite journal |author=Ren RB, Costantini F, Gorgacz EJ, Lee JJ, Racaniello VR |title=Transgenic mice expressing a human poliovirus receptor: a new model for poliomyelitis |journal=Cell |volume=63 |issue=2 |pages=353-62 |year=1990 |pmid=2170026 |doi=}}</ref><ref name="pmid1846972">{{cite journal |author=Koike S, Taya C, Kurata T, ''et al'' |title=Transgenic mice susceptible to poliovirus |url= http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=1846972 |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=88 |issue=3 |pages=951-5 |year=1991 |pmid=1846972 |doi=}}</ref>
-Unlike normal mice, [[transgenic]] poliovirus receptor (TgPVR) mice are susceptible to poliovirus injected [[intravenously]] or [[intramuscularly]], and when injected directly into the [[spinal cord]] or the [[brain]].<ref name="pmid8289371">{{cite journal |author=Horie H, Koike S, Kurata T, ''et al'' |title=Transgenic mice carrying the human poliovirus receptor: new animal models for study of poliovirus neurovirulence | url= http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=8289371| journal=J. Virol. |volume=68 |issue=2 |pages=681-8 |year=1994 |pmid=8289371 |doi=}}</ref> Upon infection, TgPVR mice show signs of paralysis that resemble those of poliomyelitis in humans and monkeys, and the central nervous systems of paralyzed mice are [[Histopathology|histocytochemically]] similar to those of humans and monkeys. This mouse model of human poliovirus infection has proven to be an invaluable tool in understanding poliovirus biology and pathogenicity.<ref name="pmid11597452">{{cite journal |author=Ohka S, Nomoto A |title=Recent insights into poliovirus pathogenesis |journal=Trends Microbiol. |volume=9 |issue=10 |pages=501-6 |year=2001 |pmid=11597452 |doi=}}</ref>
-Three distinct types of TgPVR mice have been well studied:<ref name="pmid7832641">{{cite journal |author=Koike S, Taya C, Aoki J, ''et al'' |title=Characterization of three different transgenic mouse lines that carry human poliovirus receptor gene--influence of the transgene expression on pathogenesis |journal=Arch. Virol. |volume=139 |issue=3-4 |pages=351-63 |year=1994 |pmid=7832641 |doi=}}</ref>
-*In TgPVR1 mice the transgene encoding the human PVR was incorporated into mouse [[chromosome]] 4. These mice express the highest levels of the transgene and the highest sensitivity to poliovirus. TgPVR1 mice are susceptible to poliovirus through the intraspinal, intracerebral, intramuscular, and intravenous pathways, but not through the oral route.
-*TgPVR21 mice have incorporated the human PVR at chromosome 13. These mice are less susceptible to poliovirus infection through the intracerebral route, possibly because they express decreased levels of hPVR. TgPVR21 mice have been shown to be susceptible to poliovirus infection through intranasal inoculation, and may be useful as a [[mucosa]]l infection model.<ref name="pmid15033568">{{cite journal |author=Nagata N, Iwasaki T, Ami Y, ''et al'' |title=A poliomyelitis model through mucosal infection in transgenic mice bearing human poliovirus receptor, TgPVR21 |journal=Virology |volume=321 |issue=1 |pages=87-100 |year=2004 |pmid=15033568 |doi=10.1016/j.virol.2003.12.008}}</ref>
-*In TgPVR5 mice the human transgene is located on chromosome 12.  These mice exhibit the lowest levels of hPVR expression and are the least susceptible to poliovirus infection.
-Recently a forth TgPVR mouse model was developed.  These "cPVR" mice carry hPVR [[cDNA]], driven by a β-[[actin]] [[promoter]], and have proven susceptible to poliovirus through intracerebral, intramuscular, and intranasal routes. In addition, these mice are capable of developing the [[Poliomyelitis#Bulbar polio|bulbar form of polio]] after intranasal inoculation.<ref name="pmid15033568"/>
-The development of the TgPVR mouse has had a profound effect on oral [[poliovirus vaccine]] (OPV) production. Previously, monitoring the safety of OPV had to be performed using monkeys, because only primates are susceptible to the virus. In 1999 the [[World Health Organization]] approved the use of the TgPVR mouse as an alternative method of assessing the effectiveness of the vaccine against poliovirus type-3. In 2000 the mouse model was approved for tests of vaccines against type-1 and type-2 poliovirus.<ref name="pmid12764491">{{cite journal |author=Dragunsky E, Nomura T, Karpinski K, ''et al'' |title=Transgenic mice as an alternative to monkeys for neurovirulence testing of live oral poliovirus vaccine: validation by a WHO collaborative study |url= http://www.scielosp.org/scielo.php?script=sci_arttext&pid=S0042-96862003000400006&lng=en&nrm=iso&tlng=en |journal=Bull. World Health Organ. |volume=81 |issue=4 |pages=251-60 |year=2003 |pmid=12764491 |doi=}}</ref>
-== Cloning and synthesis ==
-[[Image:Polyovirus.jpg|thumb|left|The structural appearance of Poliovirus.]]
-In 1981 Racaniello and Baltimore used recombinant DNA technology to generate the first infectious [[Molecular cloning|clone]] of an animal RNA virus, poliovirus.  DNA encoding the RNA genome of poliovirus was introduced into cultured mammalian cells and infectious poliovirus was produced.<ref>{{cite journal |author=Racaniello V, Baltimore D |title=Cloned poliovirus complemenatry DNA is infectious in mammalian cells |journal=Science |volume=214 |issue=453 |pages=916-919 |year=1981 |pmid=6272391}}</ref> Creation of the infectious clone propelled understanding of poliovirus biology, and has become a standard technology used to study many other viruses.
-In 2002 researchers at [[SUNY Stony Brook]] succeeded in synthesizing poliovirus from its chemical code, producing the world's first synthetic virus.<ref>{{cite journal |author=Cello J, Paul AV, Wimmer E |title=Chemical synthesis of poliovirus cDNA: generation of infectious virus in the absence of natural template |journal=Science |volume=297 |issue=5583 |pages=1016-8 |year=2002 |pmid=12114528 |doi=10.1126/science.1072266}}</ref> Using the published [[genetic code]], the scientists first converted poliovirus's RNA sequence into a DNA sequence, and short fragments of the DNA sequence were assembled. The complete virus was then assembled by a [[gene synthesis]] company. Nineteen [[Marker gene|markers]] were incorporated into the synthesized DNA, so that it could be distinguished from natural poliovirus. [[Enzyme]]s were used to convert the DNA back into RNA, its natural state. The newly minted synthetic virus was injected into PVR transgenic mice, to determine if the synthetic version was able to cause disease.  The synthetic virus was able to replicate, infect, and cause paralysis or death in mice.  However, the synthetic version was between 1,000 and 10,000 times less lethal than the original virus.<ref>{{cite journal |author=Couzin J |title=Virology. Active poliovirus baked from scratch |journal=Science |volume=297 |issue=5579 |pages=174-5 |year=2002 |pmid=12114601 |doi=10.1126/science.297.5579.174b}}</ref>
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