View source for Medicine:Poliomyelitis

{{pp-semi-indef}}
{{Infobox medical condition (new)
| name          = Poliomyelitis
| synonyms      = Polio, infantile paralysis
| image         = Polio lores134.jpg
| caption       = A man with a smaller right leg due to poliomyelitis
| field         = [[Biology:Neurology|Neurology]], [[Medicine:Infectious disease (medical specialty)|infectious disease]]
| pronounce     = {{IPAc-en|ˌ|p|oʊ|l|i|oʊ|ˌ|m|aɪ|ə|'|l|aɪ|t|ɪ|s}}
| symptoms      = [[Medicine:Muscle weakness|Muscle weakness]] resulting in an inability to move<ref name = PinkBook2009/>
| complications = [[Medicine:Post-polio syndrome|Post-polio syndrome]]<ref name=NIH2014Post/>
| onset         = Few hours to days<ref name = PinkBook2009/><ref name=WHO2014/>
| duration      = 
| causes        = [[Biology:Poliovirus|Poliovirus]] spread by fecal-oral route<ref name = PinkBook2009/>
| risks         = 
| diagnosis     = Finding the virus in the [[Biology:Feces|feces]] or [[Biology:Antibodies|antibodies]] in the blood<ref name = PinkBook2009/>
| differential  = 
| prevention    = [[Engineering:Polio vaccine|Polio vaccine]]<ref name=WHO2014/>
| treatment     = Supportive care<ref name=WHO2014/>
| medication    = 
| prognosis     = 
| frequency     = 113 people (2017)<ref name=WHO2017Cases/>
| deaths        = 
}}
<!-- Definition and symptoms -->
'''Poliomyelitis''', often called '''polio''' or '''infantile paralysis''', is an [[Medicine:Infectious disease|infectious disease]] caused by the [[Biology:Poliovirus|poliovirus]].<ref name = PinkBook2009/> In about 0.5 percent of cases there is [[Medicine:Muscle weakness|muscle weakness]] resulting in an inability to move.<ref name = PinkBook2009/> This can occur over a few hours to a few days.<ref name = PinkBook2009/><ref name=WHO2014/> The weakness most often involves the legs but may less commonly involve the muscles of the head, neck and diaphragm.<ref name = PinkBook2009/> Many people fully recover.<ref name = PinkBook2009/> In those with muscle weakness about 2 to 5 percent of children and 15 to 30 percent of adults die.<ref name=PinkBook2009>{{Citation | veditors = Hamborsky J, Kroger A, Wolfe C | chapter = Poliomyelitis | title = Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book) | edition = 13th | at = (chap.&nbsp;18) | publisher = Public Health Foundation | location = Washington DC | year = 2015 | chapter-url = https://www.cdc.gov/vaccines/pubs/pinkbook/polio.html | url = https://www.cdc.gov/vaccines/pubs/pinkbook/index.html | deadurl = no | archiveurl = https://web.archive.org/web/20161230001534/https://www.cdc.gov/vaccines/pubs/pinkbook/index.html | archivedate = 30 December 2016 | df = dmy-all }}.</ref> Another 25 percent of people have minor symptoms such as fever and a sore throat and up to 5 percent have [[Medicine:Headache|headache]], neck stiffness and pains in the arms and legs.<ref name = PinkBook2009/><ref name=WHO2014/> These people are usually back to normal within one or two weeks.<ref name = PinkBook2009/> In up to 70 percent of infections [[Medicine:Asymptomatic|there are no symptoms]].<ref name = PinkBook2009/> Years after recovery [[Medicine:Post-polio syndrome|post-polio syndrome]] may occur, with a slow development of muscle weakness similar to that which the person had during the initial infection.<ref name=NIH2014Post>{{cite web|title=Post-Polio Syndrome Fact Sheet|url=http://www.ninds.nih.gov/disorders/post_polio/detail_post_polio.htm|publisher=NIH|accessdate=4 November 2014|date=16 April 2014|deadurl=yes|archiveurl=https://web.archive.org/web/20110729090555/http://www.ninds.nih.gov/disorders/post_polio/detail_post_polio.htm|archivedate=29 July 2011}}</ref>

<!-- Cause and diagnosis -->
Poliovirus is usually spread from person to person through infected fecal matter entering the mouth.<ref name = PinkBook2009/> It may also be spread by food or water containing human feces and less commonly from infected [[Biology:Saliva|saliva]].<ref name = PinkBook2009/><ref name=WHO2014/> Those who are infected may spread the disease for up to six weeks even if no symptoms are present.<ref name = PinkBook2009/> The disease may be diagnosed by finding the virus in the [[Biology:Feces|feces]] or detecting [[Biology:Antibodies|antibodies]] against it in the blood.<ref name = PinkBook2009/> The disease only occurs naturally in humans.<ref name = PinkBook2009/>

<!-- Prevention, treatment and epidemiology -->
The disease is preventable with the [[Engineering:Polio vaccine|polio vaccine]]; however, multiple doses are required for it to be effective.<ref name=WHO2014/> The US Centers for Disease Control and Prevention recommends polio vaccination boosters for travelers and those who live in countries where the disease is occurring.<ref>{{cite web|title=Guidance to US Clinicians Regarding New WHO Polio Vaccination Requirements for Travel by Residents of and Long-term Visitors to Countries with Active Polio Transmission|url=http://emergency.cdc.gov/han/han00362.asp|website=CDC|accessdate=4 June 2014|date=2 June 2014|deadurl=yes|archiveurl=https://web.archive.org/web/20140604000158/http://emergency.cdc.gov/han/han00362.asp|archivedate=4 June 2014|df=dmy-all}}</ref> Once infected there is no specific treatment.<ref name=WHO2014/> In 2016, there were 37 cases of wild polio and 5 cases of vaccine-derived polio.<ref name=WHO2014>{{cite web|title=Poliomyelitis Fact sheet N°114|url=http://www.who.int/mediacentre/factsheets/fs114/en/|website=who.int|accessdate=3 November 2014|date=October 2014|deadurl=no|archiveurl=https://web.archive.org/web/20170418105535/http://www.who.int/mediacentre/factsheets/fs114/en/|archivedate=18 April 2017}}</ref><ref name="PolioThisWeek">{{cite web|url=http://polioeradication.org/polio-today/polio-now/this-week/|title=Polio This Week|last=|first=|date=|website=|publisher=Global Polio Eradication Initiative|access-date=9 January 2018}}</ref> This is down from 350,000 wild cases in 1988.<ref name=WHO2014/> In 2014 the disease was only spreading between people in Afghanistan, Nigeria, and {{wipe|Pakistan}}.<ref name=WHO2014/> In 2015 Nigeria had stopped the spread of wild poliovirus but it reoccurred in 2016.<ref>{{Cite web|title = WHO Removes Nigeria from Polio-Endemic List|url = http://www.who.int/mediacentre/news/releases/2015/nigeria-polio/en/|website = www.who.int|accessdate = 28 September 2015|deadurl = no|archiveurl = https://web.archive.org/web/20150927225439/http://www.who.int/mediacentre/news/releases/2015/nigeria-polio/en/|archivedate = 27 September 2015|df = dmy-all}}</ref><ref name=Nigeria2016>{{cite web|title=Government of Nigeria reports 2 wild polio cases, first since July 2014|url=http://www.who.int/mediacentre/news/releases/2016/nigeria-polio/en/|website=WHO|accessdate=15 August 2016|date=11 August 2016|deadurl=no|archiveurl=https://web.archive.org/web/20160815045938/http://www.who.int/mediacentre/news/releases/2016/nigeria-polio/en/|archivedate=15 August 2016}}</ref>

<!-- History, society and culture -->
Poliomyelitis has existed for thousands of years, with depictions of the disease in ancient art.<ref name = PinkBook2009/> The disease was first recognized as a distinct condition by the English [[Medicine:Physician|physician]] Michael Underwood in 1789<ref name = PinkBook2009/> and the virus that causes it was first identified in 1908 by the Austrian immunologist [[Biography:Karl Landsteiner|Karl Landsteiner]].<ref>{{cite book|editor-last1=Daniel|editor-first1=Thomas M.|editor-last2=Robbins|editor-first2=Frederick C.|title=Polio|date=1999|publisher=University of Rochester Press|location=Rochester, N.Y.|isbn=9781580460668|page=11|edition=1st|url=https://books.google.com/books?id=BTQKnkpN6qQC&pg=PA11|deadurl=no|archiveurl=https://web.archive.org/web/20160617223604/https://books.google.com/books?id=BTQKnkpN6qQC&pg=PA11|archivedate=17 June 2016}}</ref> Major [[Medicine:Epidemic|outbreak]]s started to occur in the late 19th century in Europe and the United States.<ref name = PinkBook2009/> In the 20th century it became one of the most worrying childhood diseases in these areas.<ref>{{cite book|editor-last1=Wheeler|editor-first1=Derek S.|editor-last2=Wong|editor-first2=Hector R.|editor-first3=Thomas P.|editor-last3=Shanley|title=Science and practice of pediatric critical care medicine|date=2009|publisher=Springer|location=London|isbn=9781848009219|pages=10–11|url=https://books.google.com/books?id=3p7jezlQ0zgC&pg=PA11|deadurl=no|archiveurl=https://web.archive.org/web/20160617234650/https://books.google.com/books?id=3p7jezlQ0zgC&pg=PA11|archivedate=17 June 2016}}</ref> The first polio vaccine was developed in the 1950s by Jonas Salk.<ref name=Aylward_2006>{{cite journal |author=Aylward R |title=Eradicating polio: today's challenges and tomorrow's legacy |journal=Annals of Tropical Medicine and Parasitology |volume=100 |issue=5–6 |pages=401–13 |year=2006 |pmid=16899145 | doi = 10.1179/136485906X97354}}</ref> It was hoped that [[Biology:Vaccination|vaccination]] efforts and early detection of cases would result in global [[Medicine:Poliomyelitis eradication|eradication]] of the disease by 2018.<ref>{{cite web|title=Global leaders support new six-year plan to deliver a polio-free world by 2018|url=http://www.who.int/mediacentre/news/releases/2013/polio_six_year_plan_20130425/en/|website=who.int|accessdate=4 November 2014|date=25 April 2013|deadurl=no|archiveurl=https://web.archive.org/web/20141018020329/http://www.who.int/mediacentre/news/releases/2013/polio_six_year_plan_20130425/en/|archivedate=18 October 2014}}</ref>

== Signs and symptoms ==
{| class = "wikitable" style = "float:right; font-size:90%; margin-left:15px"
|+'''Outcomes of poliovirus infection'''
|-
! style="background:#efefef;" | Outcome
! style="background:#efefef" | Proportion of cases<ref name = PinkBook2009/>
|-
| No symptoms
| style="text-align:center;"|72%
|-
| Minor illness
| style="text-align:center;"|24%
|-
|Nonparalytic aseptic<br /> meningitis
| style="text-align:center;"|1–5%
|-
|Paralytic poliomyelitis
| style="text-align:center;"|0.1–0.5%
|-
|— Spinal polio
| style="text-align:center;"|79% of paralytic cases
|-
|— Bulbospinal polio
| style="text-align:center;"|19% of paralytic cases
|-
|— Bulbar polio
| style="text-align:center;"|2% of paralytic cases
|}

The term "poliomyelitis" is used to identify the disease caused by any of the three serotypes of poliovirus. Two basic patterns of polio infection are described: a minor illness which does not involve the [[Biology:Central nervous system|central nervous system]] (CNS), sometimes called abortive poliomyelitis, and a major illness involving the CNS, which may be paralytic or nonparalytic.<ref>{{cite journal |vauthors=Falconer M, Bollenbach E |title=Late functional loss in nonparalytic polio |journal=American Journal of Physical Medicine & Rehabilitation |volume=79 |issue=1 |pages=19–23 |year=2000 |pmid=10678598 |doi=10.1097/00002060-200001000-00006}}</ref> In most people with a normal immune system, a poliovirus infection is [[Medicine:Subclinical infection|asymptomatic]]. Rarely, the infection produces minor symptoms; these may include upper [[Medicine:Respiratory tract|respiratory tract]] infection ([[Medicine:Pharyngitis|sore throat]] and fever), gastrointestinal disturbances (nausea, vomiting, [[Medicine:Abdominal pain|abdominal pain]], constipation or, rarely, diarrhea), and [[Biology:Influenza-like illness|influenza-like illness]].<ref name="PinkBook2009" />

The virus enters the central nervous system in about 1 percent of infections. Most patients with CNS involvement develop nonparalytic aseptic meningitis, with symptoms of headache, neck, back, abdominal and extremity pain, fever, vomiting, lethargy, and irritability.<ref name=Chamberlin_2005 /><ref name=Late>{{cite book | author=Leboeuf C | title=The late effects of Polio: Information For Health Care Providers. | url = http://www.health.qld.gov.au/polio/gp/GP_Manual.pdf| format=PDF | publisher=Commonwealth Department of Community Services and Health |year = 1992 |isbn=1-875412-05-0| accessdate=23 August 2008|archiveurl = https://web.archive.org/web/20080625212726/http://www.health.qld.gov.au/polio/gp/GP_Manual.pdf |archivedate = 25 June 2008|deadurl=yes}}</ref> About one to five in 1000 cases progress to paralytic disease, in which the muscles become weak, floppy and poorly controlled, and, finally, completely paralyzed; this condition is known as acute flaccid paralysis.<ref name=Henry1 />  Depending on the site of paralysis, paralytic poliomyelitis is classified as spinal, bulbar, or bulbospinal. [[Medicine:Encephalitis|Encephalitis]], an infection of the brain tissue itself, can occur in rare cases, and is usually restricted to infants. It is characterized by confusion, changes in mental status, headaches, fever, and, less commonly, [[Medicine:Seizure|seizure]]s and spastic paralysis.<ref name= Encephalitis>{{cite book |author1=Wood, Lawrence D. H. |author2=Hall, Jesse B. |author3=Schmidt, Gregory D. |title=Principles of Critical Care |edition=3rd |publisher=McGraw-Hill Professional |location= |year=2005 |page=870 |isbn=0-07-141640-4 }}</ref>

== Cause ==
{{main|Biology:Poliovirus}}
[[File:Polio EM PHIL 1875 lores.PNG|thumb|right|A [[Engineering:Transmission electron microscopy|TEM]] [[Micrograph|micrograph]] of poliovirus]]

Poliomyelitis is caused by infection with a member of the [[Biology:Genus|genus]] ''[[Biology:Enterovirus|Enterovirus]]'' known as [[Biology:Poliovirus|poliovirus]] (PV). This group of [[Biology:RNA virus|RNA virus]]es colonize the gastrointestinal tract<ref name=Harrison>{{cite book| author = Cohen JI| chapter = Chapter 175: Enteroviruses and Reoviruses| title = Harrison's Principles of Internal Medicine|editor1=Kasper DL |editor2=Braunwald E |editor3=Fauci AS |display-editors=etal | edition = 16th | publisher = McGraw-Hill Professional| year = 2004| page = 1144| isbn = 0-07-140235-7 }}</ref> — specifically the oropharynx and the [[Chemistry:Intestine|intestine]]. The incubation time (to the first signs and symptoms) ranges from three to 35 days, with a more common span of six to 20 days.<ref name="PinkBook2009" /> PV [[Biology:Pathogen|infects and causes disease]] in humans alone.<ref name=Sherris>{{cite book | veditors = Ryan KJ, Ray CG | chapter = Enteroviruses | title = Sherris Medical Microbiology | edition = 4th | pages = 535–7 | publisher = McGraw Hill | year = 2004 | isbn = 0-8385-8529-9 }}</ref> Its structure is very simple, composed of a single [[Biology:Sense (molecular biology)|(+) sense]] [[Biology:RNA|RNA]] [[Biology:Genome|genome]] enclosed in a protein shell called a [[Biology:Capsid|capsid]].<ref name=Sherris /> In addition to protecting the virus’s genetic material, the capsid proteins enable poliovirus to infect certain types of cells. Three serotypes 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 |author1=Katz, Samuel L. |author2=Gershon, Anne A. |author3=Krugman, Saul |author4=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 }}</ref> All three are extremely [[Biology:Virulence|virulent]] and produce the same disease symptoms.<ref name=Sherris /> PV1 is the most commonly encountered form, and the one most closely associated with paralysis.<ref name= Ohri/>

Individuals who are exposed to the virus, either through infection or by [[Biology:Immunization|immunization]] with polio vaccine, develop [[Medicine:Immunity (medical)|immunity]].  In immune individuals, IgA [[Biology:Antibodies|antibodies]] against poliovirus are present in the [[Biology:Tonsil|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 [[Biology:Central nervous system|central nervous system]].<ref name=Kew_2005/> Infection or vaccination with one serotype of poliovirus does not provide immunity against the other serotypes, and full immunity requires exposure to each serotype.<ref name=Kew_2005/>

A rare condition with a similar presentation, nonpoliovirus poliomyelitis, may result from infections with nonpoliovirus [[Biology:Enterovirus|enterovirus]]es.<ref>{{cite journal |vauthors=Gorson KC, Ropper AH |title=Nonpoliovirus poliomyelitis simulating Guillain–Barré syndrome |journal=Archives of Neurology |volume=58 |issue=9 |pages=1460–4 |date=September 2001 |pmid=11559319 |doi=10.1001/archneur.58.9.1460 |url=http://archneur.jamanetwork.com/article.aspx?articleid=780244 |deadurl=no |archiveurl=https://web.archive.org/web/20130419074833/http://archneur.jamanetwork.com/article.aspx?articleid=780244 |archivedate=19 April 2013  }}</ref>

=== Transmission ===
Poliomyelitis is highly contagious via the fecal-oral (intestinal source) and the oral-oral (oropharyngeal source) routes.<ref name=Kew_2005>{{cite journal |vauthors=Kew O, Sutter R, de Gourville E, Dowdle W, Pallansch M |title=Vaccine-derived polioviruses and the endgame strategy for global polio eradication |journal=Annual Review of Microbiology |volume=59 |issue= |pages=587–635 |year=2005 |pmid=16153180 |doi=10.1146/annurev.micro.58.030603.123625}}</ref> In endemic areas, wild polioviruses can infect virtually the entire human population.<ref name=McGraw>{{cite book |editor = Parker SP | title = McGraw-Hill Concise Encyclopedia of Science & Technology |publisher=McGraw-Hill |location=New York |year=1998 | isbn=0-07-052659-1| page= 67}}</ref> It is seasonal in [[Earth:Temperate climate|temperate climate]]s, with peak transmission occurring in summer and autumn.<ref name=Kew_2005 /> These seasonal differences are far less pronounced in [[Earth:Tropical climate|tropical]] areas.<ref name=McGraw /> The time between first exposure and first symptoms, known as the [[Medicine:Incubation period|incubation period]], is usually 6 to 20&nbsp;days, with a maximum range of 3 to 35&nbsp;days.<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 |doi=10.1016/j.virol.2005.09.015}}</ref> Virus particles are excreted in the [[Biology:Feces|feces]] for several weeks following initial infection.<ref name=Racaniello /> The disease is [[Medicine:Transmission|transmitted]] primarily via the fecal-oral route, by ingesting contaminated food or water. It is occasionally transmitted via the oral-oral route,<ref name= Ohri>{{cite journal |last= Ohri |first=Linda K. |author2=Jonathan G. Marquess |year=1999 |title= Polio: Will We Soon Vanquish an Old Enemy? |journal= Drug Benefit Trends |volume= 11 |issue= 6|pages=41–54 |id= |url=http://www.medscape.com/viewarticle/416890 |accessdate= 23 August 2008 |archiveurl = https://web.archive.org/web/20040204232019/http://www.medscape.com/viewarticle/416890 |archivedate=4 February 2004 |deadurl=yes}} (Available free on [[Medicine:Medscape|Medscape]]; registration required.)</ref> a mode especially visible in areas with good sanitation and hygiene.<ref name=Kew_2005 /> Polio is most infectious between 7 and 10 days before and after the appearance of symptoms, but transmission is possible as long as the virus remains in the saliva or feces.<ref name= Ohri/>

Factors that increase the risk of polio infection or affect the severity of the disease include immune deficiency,<ref>{{cite journal |doi=10.1056/NEJM197708042970503 |vauthors=Davis L, Bodian D, Price D, Butler I, Vickers J |title=Chronic progressive poliomyelitis secondary to vaccination of an immunodeficient child |journal=New England Journal of Medicine |volume=297 |issue=5 |pages=241–5 |year=1977 |pmid = 195206}}</ref> [[Medicine:Malnutrition|malnutrition]],<ref>{{cite journal |author=Chandra R |title=Reduced secretory antibody response to live attenuated measles and poliovirus vaccines in malnourished children |pmc=1673535 |journal=British Medical Journal |volume=2 |issue=5971 |pages=583–5 |pmid=1131622 |date=14 June 1975 |doi=10.1136/bmj.2.5971.583}}</ref> physical activity immediately following the onset of paralysis,<ref>{{cite journal |author=Horstmann D |title=Acute poliomyelitis relation of physical activity at the time of onset to the course of the disease |journal=Journal of the American Medical Association |volume=142 |issue=4 |pages=236–41 |year=1950 |pmid=15400610 |doi=10.1001/jama.1950.02910220016004}}</ref> skeletal muscle injury due to [[Biology:Intramuscular injection|injection]] of vaccines or therapeutic agents,<ref>{{cite journal |vauthors=Gromeier M, Wimmer E |title=Mechanism of Injury-Provoked Poliomyelitis |pmc=110068 | journal=Journal of Virology |volume=72 |issue=6 |pages=5056–60 |year=1998 |pmid=9573275 }}</ref> and [[Medicine:Pregnancy|pregnancy]].<ref name=Evans_1960>{{cite journal |author=Evans C |title=Factors influencing the occurrence of illness during naturally acquired poliomyelitis virus infections |url=http://mmbr.asm.org/cgi/reprint/24/4/341.pdf |format=PDF |journal=Bacteriology Reviews |volume=24 |issue=4 |pages=341–52 |year=1960 |pmid=13697553 |pmc=441061 |deadurl=no |archiveurl=https://web.archive.org/web/20070621131041/http://mmbr.asm.org/cgi/reprint/24/4/341.pdf |archivedate=21 June 2007  }}</ref> Although the virus can cross the [[Biology:Placenta|maternal-fetal barrier]] during pregnancy, the fetus does not appear to be affected by either maternal infection or polio vaccination.<ref name=UK>{{cite book |veditors=((Joint Committee on Vaccination and Immunisation)), Salisbury A, Ramsay M, Noakes K |title=Chapter 26:Poliomyelitis. ''in:'' Immunisation Against Infectious Disease, 2006 |url=http://www.immunisation.nhs.uk/files/GB_26_polio.pdf |format=PDF |publisher=Stationery Office |location=Edinburgh |year=2006 |pages=313–29 |isbn=0-11-322528-8 |deadurl=no |archiveurl=https://web.archive.org/web/20090326085852/http://www.immunisation.nhs.uk/files/GB_26_polio.pdf |archivedate=26 March 2009  }}</ref> Maternal antibodies also cross the [[Biology:Placenta|placenta]], providing [[Biology:Passive immunity|passive immunity]] that protects the infant from polio infection during the first few months of life.<ref>{{cite journal |vauthors=Sauerbrei A, Groh A, Bischoff A, Prager J, Wutzler P |title=Antibodies against vaccine-preventable diseases in pregnant women and their offspring in the eastern part of Germany |journal=Medical Microbiology and Immunology |volume=190 |issue=4 |pages=167–72 |year=2002 |pmid=12005329 |doi=10.1007/s00430-001-0100-3}}</ref>

As a precaution against infection, public [[Earth:Swimming pool|swimming pool]]s were often closed in affected areas during poliomyelitis epidemics.

== Pathophysiology ==
[[File:Polio spine.png|thumb|left|A blockage of the lumbar anterior spinal cord artery due to polio (PV3)]]

Poliovirus enters the body through the mouth, infecting the first cells with which it comes in contact — the pharynx and intestinal mucosa. It gains entry by binding to an immunoglobulin-like receptor, known as the poliovirus receptor or [[Biology:CD155|CD155]], on the cell membrane.<ref name=He>{{cite journal |vauthors=He Y, Mueller S, Chipman P, etal |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=Journal of Virology |volume=77 |issue=8 |pages=4827–35 |year=2003 |pmid=12663789 |doi=10.1128/JVI.77.8.4827-4835.2003 |pmc=152153 |deadurl=no |archiveurl=https://web.archive.org/web/20070905211036/http://jvi.asm.org/cgi/content/full/77/8/4827?view=long&pmid=12663789 |archivedate=5 September 2007  }}</ref> The virus then hijacks the [[Biology:Host|host cell's]] own machinery, and begins to [[Biology:Viral replication|replicate]]. Poliovirus divides within gastrointestinal cells for about a week, from where it spreads to the tonsils (specifically the follicular dendritic cells residing within the tonsilar germinal centers), the intestinal lymphoid tissue including the [[Biology:Microfold cell|M cells]] of Peyer's patches, and the deep cervical and mesenteric lymph nodes, where it multiplies abundantly. The virus is subsequently absorbed into the bloodstream.<ref name=Baron>{{cite book| vauthors = Yin-Murphy M, Almond JW| chapter = Picornaviruses: The Enteroviruses: Polioviruses| title = Baron's Medical Microbiology| editor = Baron S| display-editors = etal| edition = 4th| publisher = Univ of Texas Medical Branch| year = 1996| url = https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.2862| isbn = 0-9631172-1-1| deadurl = no| archiveurl = https://web.archive.org/web/20081207154734/http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.2862| archivedate = 7 December 2008| df = dmy-all}}</ref>

Known as [[Medicine:Viremia|viremia]], the presence of a virus in the bloodstream enables it to be widely distributed throughout the body. Poliovirus can survive and multiply within the blood and lymphatics for long periods of time, sometimes as long as 17 weeks.<ref>{{cite web | author = Todar K | title = Polio | work = Ken Todar's Microbial World | publisher = University of Wisconsin – Madison | year = 2006 | url = http://textbookofbacteriology.net/themicrobialworld/Polio.html | accessdate = 23 April 2007 | deadurl = yes | archiveurl = https://web.archive.org/web/20100427041918/http://textbookofbacteriology.net/themicrobialworld/Polio.html | archivedate = 27 April 2010 | df = dmy-all }}</ref> In a small percentage of cases, it can spread and replicate in other sites, such as brown fat, the reticuloendothelial tissues, and muscle.<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 |doi=10.1126/science.123.3209.1151}}</ref> This sustained replication causes a major viremia, and leads to the development of minor influenza-like symptoms. Rarely, this may progress and the virus may invade the central nervous system, provoking a local inflammatory response. In most cases, this causes a self-limiting inflammation of the [[Medicine:Meninges|meninges]], the layers of tissue surrounding the [[Biology:Human brain|brain]], which is known as nonparalytic aseptic meningitis.<ref name=Chamberlin_2005 /> Penetration of the CNS provides no known benefit to the virus, and is quite possibly an incidental deviation of a normal gastrointestinal infection.<ref name= Mueller>{{cite journal |vauthors=Mueller S, Wimmer E, Cello J |title=Poliovirus and poliomyelitis: a tale of guts, brains, and an accidental event |journal=Virus Research |volume=111 |issue=2 |pages=175–93 |year=2005 |pmid = 15885840 | doi = 10.1016/j.virusres.2005.04.008}}</ref> The mechanisms by which poliovirus spreads to the CNS are poorly understood, but it appears to be primarily a chance event—largely independent of the age, gender, or socioeconomic position of the individual.<ref name=Mueller />

=== Paralytic polio ===
[[File:PHIL 2767 Poliovirus Myotonic dystrophic changes.jpg|thumb|right|Denervation of [[Biology:Skeletal muscle|skeletal muscle]] tissue secondary to poliovirus infection can lead to paralysis.]]

In around 1 percent of infections, poliovirus spreads along certain nerve fiber pathways, preferentially replicating in and destroying motor neurons within the [[Biology:Spinal cord|spinal cord]], brain stem, or [[Biology:Motor cortex|motor cortex]]. This leads to the development of paralytic poliomyelitis, the various forms of which (spinal, bulbar, and bulbospinal) vary only with the amount of neuronal damage and inflammation that occurs, and the region of the CNS affected.

The destruction of neuronal cells produces [[Medicine:Lesion|lesion]]s within the spinal ganglia; these may also occur in the [[Biology:Reticular formation|reticular formation]], vestibular nuclei, [[Biology:Cerebellar vermis|cerebellar vermis]], and deep cerebellar nuclei.<ref name=Mueller />  Inflammation associated with [[Biology:Neuron|nerve cell]] destruction often alters the color and appearance of the gray matter in the spinal column, causing it to appear reddish and swollen.<ref name=Chamberlin_2005/> Other destructive changes associated with paralytic disease occur in the [[Biology:Forebrain|forebrain]] region, specifically the [[Biology:Hypothalamus|hypothalamus]] and [[Biology:Thalamus|thalamus]].<ref name=Mueller /> The molecular mechanisms by which poliovirus causes paralytic disease are poorly understood.

Early symptoms of paralytic polio include high fever, headache, stiffness in the back and neck, asymmetrical weakness of various muscles, sensitivity to touch, difficulty swallowing, [[Medicine:Myalgia|muscle pain]], loss of superficial and deep [[Biology:Reflex|reflex]]es, [[Unsolved:Paresthesia|paresthesia]] (pins and needles), irritability, constipation, or difficulty urinating. Paralysis generally develops one to ten days after early symptoms begin, progresses for two to three days, and is usually complete by the time the fever breaks.<ref name= Silverstein>{{cite book |vauthors=Silverstein A, Silverstein V, Nunn LS |title=Polio | series = Diseases and People | publisher=Enslow Publishers |location=Berkeley Heights, NJ |year=2001| isbn=0-7660-1592-0 |page= 12 }}</ref>

The likelihood of developing paralytic polio increases with age, as does the extent of paralysis. In children, nonparalytic meningitis is the most likely consequence of CNS involvement, and paralysis occurs in only one in 1000 cases. In adults, paralysis occurs in one in 75 cases.<ref name="Gawne_1995">{{cite journal|year=1995|title=Post-polio syndrome: pathophysiology and clinical management|url=http://www.poliosurvivorsnetwork.org.uk/archive/lincolnshire/library/gawne/ppspandcm.html|journal=Critical Review in Physical Medicine and Rehabilitation|volume=7|pages=147–88|vauthors=Gawne AC, Halstead LS|deadurl=yes|archiveurl=https://web.archive.org/web/20160630225919/http://www.poliosurvivorsnetwork.org.uk/archive/lincolnshire/library/gawne/ppspandcm.html|archivedate=30 June 2016|access-date=30 June 2016|df=dmy-all}} Reproduced online with permission by Lincolnshire Post-Polio Library; retrieved on 10 November 2007.</ref> In children under five years of age, paralysis of one leg is most common; in adults, extensive paralysis of the chest and [[Biology:Abdomen|abdomen]] also affecting all four limbs—[[Medicine:Quadriplegia|quadriplegia]]—is more likely.<ref name=Young>{{cite journal |author=Young GR |title=Occupational therapy and the postpolio syndrome |url=http://www.ott.zynet.co.uk/polio/lincolnshire/library/gryoung/otapps.html |journal=The American Journal of Occupational Therapy |volume=43 |issue=2 |pages=97–103 |year=1989 |pmid=2522741 |doi=10.5014/ajot.43.2.97 |deadurl=yes |archiveurl=https://web.archive.org/web/20070811122404/http://www.ott.zynet.co.uk/polio/lincolnshire/library/gryoung/otapps.html |archivedate=11 August 2007  }}</ref> Paralysis rates also vary depending on the serotype of the infecting poliovirus; the highest rates of paralysis (one in 200) are associated with poliovirus type 1, the lowest rates (one in 2,000) are associated with type 2.<ref name=Nathanson>{{cite journal |vauthors=Nathanson N, Martin J |title=The epidemiology of poliomyelitis: enigmas surrounding its appearance, epidemicity, and disappearance |journal=American Journal of Epidemiology |volume=110 |issue=6 |pages=672–92 |year=1979 |pmid=400274 |doi=10.1093/oxfordjournals.aje.a112848}}</ref>

==== Spinal polio ====
[[File:Polio spinal diagram-en.svg|thumb|left|The location of motor neurons in the anterior horn cells of the spinal column]]

Spinal polio, the most common form of paralytic poliomyelitis, results from viral invasion of the motor neurons of the anterior horn cells, or the ventral (front) [[Biology:Grey matter|grey matter]] section in the spinal column, which are responsible for movement of the muscles, including those of the trunk, limbs, and the intercostal muscles.<ref name= Henry1>{{cite book |vauthors=Frauenthal HW, Manning JV | title = Manual of infantile paralysis, with modern methods of treatment.| publisher = Philadelphia Davis | year = 1914| pages= 79–101 |url= https://books.google.com/?id=piyLQnuT-1YC&printsec=titlepage | oclc= 2078290}}</ref> Virus invasion causes inflammation of the nerve cells, leading to damage or destruction of motor neuron [[Biology:Ganglion|ganglia]]. When spinal neurons die, [[Medicine:Wallerian degeneration|Wallerian degeneration]] takes place, leading to weakness of those muscles formerly innervated by the now-dead neurons.<ref>{{Cite web|url = http://phil.cdc.gov/phil/details.asp?pid=2760|title = A photomicrograph of the thoracic spinal cord depicting degenerative changes due to Polio Type III.|date = 18 March 2005|accessdate = 24 January 2014|website = Public Health Image Library (PHIL)|publisher = Centers for Disease Control and Prevention|last = Karp|first = Dr.|deadurl = no|archiveurl = https://web.archive.org/web/20140202193927/http://phil.cdc.gov/phil/details.asp?pid=2760|archivedate = 2 February 2014|df = dmy-all}}</ref> With the destruction of nerve cells, the muscles no longer receive signals from the brain or spinal cord; without nerve stimulation, the muscles [[Medicine:Atrophy|atrophy]], becoming weak, floppy and poorly controlled, and finally completely paralyzed.<ref name=Henry1 /> Maximum paralysis progresses rapidly (two to four days), and usually involves fever and muscle pain. Deep [[Biology:Stretch reflex|tendon]] [[Biology:Reflex|reflex]]es are also affected, and are typically absent or diminished; [[Philosophy:Sense|sensation]] (the ability to feel) in the paralyzed limbs, however, is not affected.<ref>{{cite web|url = https://www.cdc.gov/vaccines/pubs/surv-manual/chpt12-polio.html|title = Chapter 12: Poliomyelitis|date = 13 April 2013|accessdate = 24 January 2014|website = Manual for the Surveillance of Vaccine-Preventable Diseases (5th Edition, 2012)|publisher = Centers for Disease Control and Prevention|last = Wallace|first2 = M. Stephen|last2 = Oberste|first = Gregory S|deadurl = no|archiveurl = https://web.archive.org/web/20140128113623/http://www.cdc.gov/vaccines/pubs/surv-manual/chpt12-polio.html|archivedate = 28 January 2014|df = dmy-all}}</ref>

The extent of spinal paralysis depends on the region of the cord affected, which may be [[Medicine:Neck|cervical]], thoracic, or [[Biology:Lumbar|lumbar]].<ref name=Guide>{{cite book |title=Professional Guide to Diseases (Professional Guide Series) |publisher=Lippincott Williams & Wilkins |location=Hagerstown, MD |year= 2005|pages=243–5 |isbn=1-58255-370-X }}</ref> The virus may affect muscles on both sides of the body, but more often the paralysis is [[Asymmetry|asymmetrical]].<ref name=Baron /> Any limb or combination of limbs may be affected—one leg, one arm, or both legs and both arms.  Paralysis is often more severe [[Biology:Anatomical terms of location#Proximal distal|proximally]] (where the limb joins the body) than [[Biology:Anatomical terms of location#Proximal distalDistally|distally]] (the fingertips and toes).<ref name=Baron />

==== Bulbar polio ====
[[File:Brain bulbar region.svg|thumb|right|The location and anatomy of the bulbar region (in orange)]]

Making up about 2 percent of cases of paralytic polio, bulbar polio occurs when poliovirus invades and destroys nerves within the bulbar region of the brain stem.<ref name = PinkBook2009 /> The bulbar region is a [[Biology:White matter|white matter]] pathway that connects the [[Biology:Cerebral cortex|cerebral cortex]] to the brain stem. The destruction of these nerves weakens the muscles supplied by the cranial nerves, producing symptoms of [[Medicine:Encephalitis|encephalitis]], and causes difficulty breathing, speaking and swallowing.<ref name=Late /> Critical nerves affected are the [[Biology:Glossopharyngeal nerve|glossopharyngeal nerve]] (which partially controls swallowing and functions in the throat, tongue movement, and taste), the [[Biology:Vagus nerve|vagus nerve]] (which sends signals to the heart, intestines, and lungs), and the [[Biology:Accessory nerve|accessory nerve]] (which controls upper neck movement). Due to the effect on swallowing, secretions of [[Biology:Mucus|mucus]] may build up in the airway, causing suffocation.<ref name = Silverstein /> Other signs and symptoms include facial weakness (caused by destruction of the [[Biology:Trigeminal nerve|trigeminal nerve]] and [[Biology:Facial nerve|facial nerve]], which innervate the cheeks, tear ducts, gums, and muscles of the face, among other structures), [[Medicine:Diplopia|double vision]], difficulty in chewing, and abnormal [[Respiratory rate|respiratory rate]], depth, and rhythm (which may lead to [[Medicine:Respiratory arrest|respiratory arrest]]). [[Medicine:Pulmonary edema|Pulmonary edema]] and [[Medicine:Shock (circulatory)|shock]] are also possible and may be fatal.<ref name=Guide/>

==== Bulbospinal polio ====
Approximately 19 percent of all paralytic polio cases have both bulbar and spinal symptoms; this subtype is called respiratory or bulbospinal polio.<ref name="PinkBook2009" /> Here, the virus affects the upper part of the cervical spinal cord (cervical vertebrae C3 through C5), and paralysis of the diaphragm occurs. The critical nerves affected are the phrenic nerve (which drives the diaphragm to inflate the lungs) and those that drive the muscles needed for swallowing. By destroying these nerves, this form of polio affects breathing, making it difficult or impossible for the patient to breathe without the support of a [[Medicine:Medical ventilator|ventilator]]. It can lead to paralysis of the arms and legs and may also affect swallowing and heart functions.<ref name= Hoyt/>

== Diagnosis ==
Paralytic poliomyelitis may be clinically suspected in individuals experiencing acute onset of flaccid paralysis in one or more limbs with decreased or absent tendon reflexes in the affected limbs that cannot be attributed to another apparent cause, and without sensory or cognitive loss.<ref>{{cite journal |title=Case definitions for infectious conditions under public health surveillance. Centers for Disease Control and Prevention |url=ftp://ftp.cdc.gov/pub/Publications/mmwr/rr/rr4610.pdf |format=PDF |journal=Morbidity and Mortality Weekly Report |volume=46 |issue=RR–10 |pages=26–7 |year=1997 |pmid=9148133 |deadurl=no |archiveurl=https://web.archive.org/web/20090810151022/http://ftp.cdc.gov/pub/Publications/mmwr/rr/rr4610.pdf |archivedate=10 August 2009  }}</ref>

A laboratory diagnosis is usually made based on recovery of poliovirus from a stool sample or a swab of the pharynx. [[Biology:Antibody|Antibodies]] to poliovirus can be diagnostic, and are generally detected in the blood of infected patients early in the course of infection.<ref name="PinkBook2009" /> Analysis of the patient's [[Biology:Cerebrospinal fluid|cerebrospinal fluid]] (CSF), which is collected by a [[Medicine:Lumbar puncture|lumbar puncture]] ("spinal tap"), reveals an increased number of [[Biology:White blood cell|white blood cell]]s (primarily [[Biology:Lymphocyte|lymphocyte]]s) and a mildly elevated protein level. Detection of virus in the CSF is diagnostic of paralytic polio, but rarely occurs.<ref name = PinkBook2009/>

If poliovirus is isolated from a patient experiencing acute flaccid paralysis, it is further tested through [[Chemistry:Oligonucleotide|oligonucleotide]] mapping (genetic fingerprinting), or more recently by [[Biology:Polymerase chain reaction|PCR]] amplification, to determine whether it is "[[Biology:Wild type|wild type]]" (that is, the virus encountered in nature) or "vaccine type" (derived from a strain of poliovirus used to produce polio vaccine).<ref>{{cite journal |author=Chezzi C |title=Rapid diagnosis of poliovirus infection by PCR amplification |pmc=229102 | journal=[[Biology:Journal of Clinical Microbiology|Journal of Clinical Microbiology]] |volume=34 |issue=7 |pages=1722–5 |pmid=8784577 |date=July 1996}}</ref>  It is important to determine the source of the virus because for each reported case of paralytic polio caused by wild poliovirus, an estimated 200 to 3,000  other contagious [[Medicine:Asymptomatic carrier|asymptomatic carrier]]s exist.<ref>{{cite journal |author= Gawande A |title = The mop-up: eradicating polio from the planet, one child at a time | work = The New Yorker | issn = 0028-792X | pages = 34–40 | date = 12 January 2004}}</ref>

== Prevention ==
=== Passive immunization ===
In 1950, William Hammon at the University of Pittsburgh purified the [[Biology:Gamma globulin|gamma globulin]] component of the [[Biology:Blood plasma|blood plasma]] of polio survivors.<ref name=Hammon_1955>{{cite journal |author=Hammon W |title=Passive immunization against poliomyelitis |journal=Monograph Series. World Health Organization |volume=26 |issue= |pages=357–70 |year = 1955 |pmid=14374581}}</ref>  Hammon proposed the gamma globulin, which contained antibodies to poliovirus, could be used to halt poliovirus infection, prevent disease, and reduce the severity of disease in other patients who had contracted polio. The results of a large [[Engineering:Clinical trial|clinical trial]] were promising; the gamma globulin was shown to be about 80 percent effective in preventing the development of paralytic poliomyelitis.<ref>{{cite journal |vauthors=Hammon W, Coriell L, Ludwig E, etal |title=Evaluation of Red Cross gamma globulin as a prophylactic agent for poliomyelitis. 5. Reanalysis of results based on laboratory-confirmed cases |journal=Journal of the American Medical Association |volume=156 |issue=1 |pages=21–7 |year=1954 |pmid=13183798 |doi=10.1001/jama.1954.02950010023009}}</ref> It was also shown to reduce the severity of the disease in patients who developed polio.<ref name=Hammon_1955 /> Due to the limited supply of blood plasma gamma globulin was later deemed impractical for widespread use and the medical community focused on the development of a polio vaccine.<ref name=Rinaldo>{{cite journal |author=Rinaldo C |title=Passive Immunization Against Poliomyelitis: The Hammon Gamma Globulin Field Trials, 1951–1953 |journal=American Journal of Public Health |volume=95 |issue=5 |pages=790–9 |year=2005 |pmid=15855454 |doi=10.2105/AJPH.2004.040790 |pmc=1449257}}</ref>

=== Vaccine ===
{{main|Engineering:Polio vaccine}}
[[File:Poliodrops.jpg|thumb|right|A child receiving an oral polio vaccine]]

Two types of vaccine are used throughout the world to combat polio. Both types induce immunity to polio, efficiently blocking person-to-person transmission of wild poliovirus, thereby protecting both individual vaccine recipients and the wider community (so-called [[Medicine:Herd immunity|herd immunity]]).<ref name=Fine>{{cite journal |vauthors=Fine P, Carneiro I |title=Transmissibility and persistence of oral polio vaccine viruses: implications for the global poliomyelitis eradication initiative |url=http://aje.oxfordjournals.org/cgi/reprint/150/10/1001 |journal=American Journal of Epidemiology |volume=150 |issue=10 |pages=1001–21 |date=15 November 1999 |pmid=10568615 |doi=10.1093/oxfordjournals.aje.a009924 |deadurl=no |archiveurl=https://web.archive.org/web/20071012201750/http://aje.oxfordjournals.org/cgi/reprint/150/10/1001 |archivedate=12 October 2007  }}</ref>

The first candidate [[Engineering:Polio vaccine|polio vaccine]], based on one serotype of a live but [[Medicine:Attenuated vaccine|attenuated (weakened) virus]], was developed by the virologist Hilary Koprowski. Koprowski's prototype vaccine was given to an eight-year-old boy on 27 February 1950.<ref>{{cite web |url=http://www.historyofvaccines.org/content/timelines/polio |title=Interview with Hilary Koprowski, sourced at History of Vaccines website |first=Hilary |last=Koprowski |date=15 October 2010 |accessdate=15 October 2010 |publisher=College of Physicians of Philadelphia |deadurl=no |archiveurl=http://arquivo.pt/wayback/20160515175017/http://www.historyofvaccines.org/content/timelines/polio |archivedate=15 May 2016  }}</ref> Koprowski continued to work on the vaccine throughout the 1950s, leading to large-scale trials in the then Belgian Congo and the vaccination of seven million children in Poland against serotypes PV1 and PV3 between 1958 and 1960.<ref name=Sanofi>{{cite web|url=http://www.polio.info/polio-eradication/front/templates/index.jsp?siteCode=POLIO&codeRubrique=34&lang=EN |title=Archived copy |accessdate=1 November 2011 |deadurl=unfit |archiveurl=https://web.archive.org/web/20071007095443/http://www.polio.info/polio-eradication/front/templates/index.jsp?siteCode=POLIO&codeRubrique=34&lang=EN |archivedate=7 October 2007 }} Accessed 16 December 2009.</ref>

The second inactivated polio virus vaccine was developed in 1952 by Jonas Salk at the University of Pittsburgh, and announced to the world on 12 April 1955.<ref name=Spice>{{cite news |author=Spice B |title=Tireless polio research effort bears fruit and indignation |url=http://www.post-gazette.com/pg/05094/482468.stm |work=The Salk vaccine: 50 years later/ second of two parts |publisher=Pittsburgh Post-Gazette |date=4 April 2005 |accessdate=23 August 2008 |deadurl=no |archiveurl=https://web.archive.org/web/20080905022100/http://www.post-gazette.com/pg/05094/482468.stm |archivedate=5 September 2008  }}</ref> The Salk vaccine, or inactivated poliovirus vaccine, is based on poliovirus grown in a type of monkey kidney [[Biology:Tissue culture|tissue culture]] ([[Biology:Vero cell|vero cell]] [[Biology:Cell culture|line]]), which is chemically inactivated with formalin.<ref name=Kew_2005 /> After two doses of inactivated poliovirus vaccine (given by [[Medicine:Injection|injection]]), 90 percent or more of individuals develop protective antibody to all three [[Biology:Serotype|serotype]]s of poliovirus, and at least 99 percent are immune to poliovirus following three doses.<ref name = PinkBook2009 />

Subsequently, Albert Sabin developed another live, oral polio vaccine. It was produced by the repeated passage of the virus through nonhuman cells at subphysiological temperatures.<ref name=Sabin_1973>{{cite journal |vauthors=Sabin AB, Boulger LR | title = History of Sabin attenuated poliovirus oral live vaccine strains | journal = Journal of Biological Standardization | year = 1973 | volume = 1 | pages = 115–8 |doi=10.1016/0092-1157(73)90048-6 | issue = 2}}</ref> The attenuated poliovirus in the Sabin vaccine replicates very efficiently in the gut, the primary site of wild poliovirus infection and replication, but the vaccine strain is unable to replicate efficiently within [[Biology:Nervous system|nervous system]] tissue.<ref>{{cite journal |vauthors=Sabin A, Ramos-Alvarez M, Alvarez-Amezquita J, etal |title=Live, orally given poliovirus vaccine. Effects of rapid mass immunization on population under conditions of massive enteric infection with other viruses |journal=Journal of the American Medical Association |volume=173 |issue= 14|pages=1521–6 |year=1960 |pmid =14440553 |doi=10.1001/jama.1960.03020320001001}}</ref> A single dose of Sabin's oral polio vaccine produces immunity to all three poliovirus serotypes in about 50 percent of recipients. Three doses of live-attenuated oral vaccine produce protective antibody to all three poliovirus types in more than 95 percent of recipients.<ref name="PinkBook2009" /> [[Engineering:Clinical trial|Human trials]] of Sabin's vaccine began in 1957,<ref name=ScienceOdyssey>{{cite web | title = A Science Odyssey: People and Discoveries | publisher = PBS | year = 1998 | url = https://www.pbs.org/wgbh/aso/databank/entries/dm52sa.html | accessdate = 23 August 2008 | deadurl = no | archiveurl = https://web.archive.org/web/20080726075448/http://www.pbs.org/wgbh/aso/databank/entries/dm52sa.html | archivedate = 26 July 2008 | df = dmy-all }}</ref> and in 1958 it was selected, in competition with the live vaccines of Koprowski and other researchers, by the US National Institutes of Health.<ref name=Sanofi/> Licensed in 1962,<ref name=ScienceOdyssey/> it rapidly became the only polio vaccine used worldwide.<ref name=Sanofi/>
[[File:Number of wild polio and cVDPV cases since 2000.png|thumb|Wild polio vs cVDVP cases]]
Because the oral polio vaccine is inexpensive, easy to administer, and produces excellent immunity in the intestine (which helps prevent infection with wild virus in areas where it is [[Medicine:Endemic (epidemiology)|endemic]]), it has been the vaccine of choice for controlling poliomyelitis in many countries.<ref name="Peds">{{cite journal |title=Poliomyelitis prevention: recommendations for use of inactivated poliovirus vaccine and live oral poliovirus vaccine. American Academy of Pediatrics Committee on Infectious Diseases |url=http://pediatrics.aappublications.org/cgi/content/full/99/2/300 |journal=Pediatrics |volume=99 |issue=2 |pages=300–5 |year=1997 |pmid=9024465 |doi=10.1542/peds.99.2.300 |deadurl=no |archiveurl=https://web.archive.org/web/20070930165356/http://pediatrics.aappublications.org/cgi/content/full/99/2/300 |archivedate=30 September 2007  }}</ref> On very rare occasions (about one case per 750,000 vaccine recipients), the attenuated virus in the oral polio vaccine reverts into a form that can paralyze.<ref name="Racaniello" />  In 2017, cases caused by vaccine-derived poliovirus (cVDPV) outnumbered wild poliovirus cases for the first time, due to wild polio cases hitting record lows and relaxed vaccination levels.<ref>{{Cite web|url=https://sphcm.med.unsw.edu.au/infectious-diseases-blog/eradication-polio-syria-being-left-behind|title=Eradication of polio – Is Syria being left behind? {{!}} School of Public Health and Community Medicine|website=sphcm.med.unsw.edu.au|language=en|access-date=2018-10-06}}</ref> Most [[Finance:Developed country|industrialized countries]] have switched to inactivated polio vaccine, which cannot revert, either as the sole vaccine against poliomyelitis or in combination with oral polio vaccine.<ref>{{cite web |url=http://www.who.int/ith/vaccines/2007_routine_use/en/index11.html |title=WHO: Vaccines for routine use |accessdate=23 August 2008 |page= 12|work= International travel and health|archiveurl = https://web.archive.org/web/20080606170542/http://www.who.int/ith/vaccines/2007_routine_use/en/index11.html |archivedate = 6 June 2008|deadurl=yes}}</ref>  

== Treatment ==
There is no [[Medicine:Cure|cure]] for polio. The focus of modern treatment has been on providing relief of symptoms, speeding recovery and preventing complications. Supportive measures include antibiotics to prevent infections in weakened muscles, analgesics for pain, moderate exercise and a nutritious diet.<ref name=Daniel>{{cite book |author1=Daniel, Thomas M. |author2=Robbins, Frederick C. |title=Polio |publisher=University of Rochester Press |location=Rochester, N.Y., USA |year= 1997 |pages= 8–10 |isbn=1-58046-066-6 }}</ref> Treatment of polio often requires long-term rehabilitation, including [[Medicine:Occupational therapy|occupational therapy]], [[Medicine:Physical therapy|physical therapy]], braces, corrective shoes and, in some cases, orthopedic surgery.<ref name=Guide />

Portable [[Engineering:Ventilator|ventilator]]s may be required to support breathing. Historically, a noninvasive, negative-pressure ventilator, more commonly called an [[Engineering:Iron lung|iron lung]], was used to artificially maintain respiration during an acute polio infection until a person could breathe independently (generally about one to two weeks). Today, many polio survivors with permanent respiratory paralysis use modern jacket-type negative-pressure ventilators worn over the chest and abdomen.<ref name= Goldberg />

Other historical treatments for polio include [[Unsolved:Hydrotherapy|hydrotherapy]], [[Chemistry:Electrotherapy|electrotherapy]], massage and passive motion exercises, and surgical treatments, such as tendon lengthening and nerve grafting.<ref name=Henry1 />

== Prognosis ==
[[File:Polio sequelle.jpg|thumb|A girl with a deformity of her right leg due to polio]]
Patients with abortive polio infections recover completely. In those who develop only aseptic meningitis, the symptoms can be expected to persist for two to ten days, followed by complete recovery.<ref name=Neumann/> In cases of spinal polio, if the affected nerve cells are completely destroyed, paralysis will be permanent; cells that are not destroyed, but lose function temporarily, may recover within four to six weeks after onset.<ref name=Neumann>{{cite journal |author=Neumann D |title=Polio: its impact on the people of the United States and the emerging profession of physical therapy |url=http://www.post-polio.org/edu/hpros/Aug04HistPersNeumann.pdf |format=PDF |journal=The Journal of Orthopaedic and Sports Physical Therapy |volume=34 |issue=8 |pages=479–92 |year=2004 |pmid=15373011 |doi=10.2519/jospt.2004.0301 |deadurl=no |archiveurl=https://web.archive.org/web/20080910165631/http://www.post-polio.org/edu/hpros/Aug04HistPersNeumann.pdf |archivedate=10 September 2008  }} Reproduced online with permission by Post-Polio Health International; retrieved on 10 November 2007.</ref> Half the patients with spinal polio recover fully; one-quarter recover with mild disability, and the remaining quarter are left with severe disability.<ref>{{cite book |author=Cuccurullo SJ |title=Physical Medicine and Rehabilitation Board Review |url=https://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=physmedrehab.table.8357 |archive-url=https://web.archive.org/web/20071012215404/http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=physmedrehab.table.8357 |dead-url=yes |archive-date=12 October 2007 |publisher=Demos Medical Publishing |year=2004 |isbn=1-888799-45-5  }}</ref> The degree of both acute paralysis and residual paralysis is likely to be proportional to the degree of [[Medicine:Viremia|viremia]], and inversely proportional to the degree of [[Medicine:Immunity (medical)|immunity]].<ref name= Mueller/> Spinal polio is rarely fatal.<ref name=Silverstein />

Without respiratory support, consequences of poliomyelitis with [[Biology:Respiration (physiology)|respiratory]] involvement include suffocation or [[Medicine:Aspiration pneumonia|pneumonia from aspiration of secretions]].<ref name= Goldberg>{{cite journal |author=Goldberg A |title=Noninvasive mechanical ventilation at home: building upon the tradition |doi=10.1378/chest.121.2.321 |journal=Chest |volume=121 |issue=2 |pages=321–4 |year=2002 |pmid=11834636}}</ref> Overall, 5 to 10 percent of patients with paralytic polio die due to the paralysis of muscles used for breathing. The [[Medicine:Case fatality rate|case fatality rate]] (CFR) varies by age: 2 to 5 percent of children and up to 15 to 30 percent of adults die.<ref name="PinkBook2009" />  Bulbar polio often causes death if respiratory support is not provided;<ref name= Hoyt /> with support, its CFR ranges from 25 to 75 percent, depending on the age of the patient.<ref name="PinkBook2009" /><ref>{{cite journal |vauthors=Miller AH, Buck LS |title=Tracheotomy in bulbar poliomyelitis |pmc=1520308 |journal=California Medicine |volume=72 |issue=1 |pages=34–6 |year=1950 |pmid=15398892 }}</ref> When intermittent positive pressure ventilation is available, the fatalities can be reduced to 15 percent.<ref name=Wackers>{{cite journal| author = Wackers, G.| title = Constructivist Medicine| version = PhD-thesis| publisher = Maastricht: Universitaire Pers Maastricht| year = 1994| url = http://www.fdcw.unimaas.nl/personal/WebSitesMWT/Wackers/proefschrift.html#h4| accessdate = 4 January 2008| deadurl = yes| archiveurl = https://web.archive.org/web/20071223223131/http://www.fdcw.unimaas.nl/personal/WebSitesMWT/Wackers/proefschrift.html#h4| archivedate = 23 December 2007| df = dmy-all}}</ref>

=== Recovery ===
Many cases of poliomyelitis result in only temporary paralysis.<ref name=Henry1 /> Nerve impulses return to the formerly paralyzed muscle within a month, and recovery is usually complete in six to eight months.<ref name=Neumann /> The [[Biology:Neurophysiology|neurophysiological]] processes involved in recovery following acute paralytic poliomyelitis are quite effective; muscles are able to retain normal strength even if half the original motor neurons have been lost.<ref>{{cite journal |vauthors=Sandberg A, Hansson B, Stålberg E |title=Comparison between concentric needle EMG and macro EMG in patients with a history of polio |journal=Clinical Neurophysiology |volume=110 |issue=11 |pages=1900–8 |year=1999 |pmid=10576485 |doi=10.1016/S1388-2457(99)00150-9}}</ref> Paralysis remaining after one year is likely to be permanent, although modest recoveries of muscle strength are possible 12 to 18 months after infection.<ref name=Neumann />

One mechanism involved in recovery is nerve terminal sprouting, in which remaining brainstem and spinal cord motor neurons develop new branches, or axonal sprouts.<ref>{{cite journal |vauthors=Cashman NR, Covault J, Wollman RL, Sanes JR |title=Neural cell adhesion molecule in normal, denervated, and myopathic human muscle |journal=Annals of Neurology |volume=21 |issue=5 |pages=481–9 |year=1987 |pmid=3296947 |doi=10.1002/ana.410210512}}</ref> These sprouts can reinnervate orphaned muscle fibers that have been denervated by acute polio infection,<ref name=Agre>{{cite journal |vauthors=Agre JC, Rodríquez AA, Tafel JA |title=Late effects of polio: critical review of the literature on neuromuscular function |journal=Archives of Physical Medicine and Rehabilitation |volume=72 |issue=11 |pages=923–31 |year=1991 |pmid=1929813 |doi=10.1016/0003-9993(91)90013-9}}</ref> restoring the fibers' capacity to contract and improving strength.<ref>{{cite journal |vauthors=Trojan DA, Cashman NR |title=Post-poliomyelitis syndrome |journal=Muscle Nerve |volume=31 |issue=1 |pages=6–19 |year=2005 |pmid=15599928 |doi=10.1002/mus.20259}}</ref> Terminal sprouting may generate a few significantly enlarged motor neurons doing work previously performed by as many as four or five units:<ref name=Gawne_1995 /> a single motor neuron that once controlled 200 muscle cells might control 800 to 1000 cells. Other mechanisms that occur during the rehabilitation phase, and contribute to muscle strength restoration, include [[Biology:Muscle hypertrophy|myofiber hypertrophy]]—enlargement of muscle fibers through exercise and activity—and transformation of type II muscle fibers to type I muscle fibers.<ref name=Agre /><ref name = Grimby_1989>{{cite journal |vauthors=Grimby G, Einarsson G, Hedberg M, Aniansson A |title=Muscle adaptive changes in post-polio subjects |journal=Scandinavian Journal of Rehabilitation Medicine |volume=21 |issue=1 |pages=19–26 |year=1989 |pmid=2711135}}</ref>

In addition to these physiological processes, the body possesses a number of compensatory mechanisms to maintain function in the presence of residual paralysis. These include the use of weaker muscles at a higher than usual intensity relative to the [[Biology:Muscle contraction#Contractions, by muscle type|muscle's maximal capacity]], enhancing athletic development of previously little-used muscles, and using [[Biology:Ligament|ligament]]s for stability, which enables greater mobility.<ref name = Grimby_1989 />

=== Complications ===
Residual complications of paralytic polio often occur following the initial recovery process.<ref name= Late /> Muscle [[Medicine:Paresis|paresis]] and paralysis can sometimes result in skeletal deformities, tightening of the joints and movement disability. Once the muscles in the limb become flaccid, they may interfere with the function of other muscles. A typical manifestation of this problem is equinus foot (similar to club foot). This deformity develops when the muscles that pull the toes downward are working, but those that pull it upward are not, and the foot naturally tends to drop toward the ground. If the problem is left untreated, the [[Medicine:Achilles tendon|Achilles tendon]]s at the back of the foot retract and the foot cannot take on a normal position. Polio victims that develop equinus foot cannot walk properly because they cannot put their heel on the ground. A similar situation can develop if the arms become paralyzed.<ref name= Aftereffects>{{cite web | author = Sanofi Pasteur | title = Poliomyelitis virus (picornavirus, enterovirus), after-effects of the polio, paralysis, deformations | work = Polio Eradication | url = http://www.polio.info/polio-eradication/front/index.jsp?siteCode=POLIO&lang=EN&codeRubrique=14 | accessdate = 23 August 2008|archiveurl = https://web.archive.org/web/20071007100336/http://www.polio.info/polio-eradication/front/index.jsp?siteCode=POLIO&lang=EN&codeRubrique=14 |archivedate = 7 October 2007|deadurl=yes}}</ref> In some cases the growth of an affected leg is slowed by polio, while the other leg continues to grow normally. The result is that one leg is shorter than the other and the person limps and leans to one side, in turn leading to deformities of the spine (such as [[Medicine:Scoliosis|scoliosis]]).<ref name= Aftereffects /> [[Medicine:Osteoporosis|Osteoporosis]] and increased likelihood of [[Medicine:Bone fracture|bone fracture]]s may occur. An intervention to prevent or lessen length disparity can be to perform an [[Medicine:Epiphysiodesis|epiphysiodesis]] on the distal femoral and proximal tibial/fibular condyles, so that limb's growth is artificially stunted, and by the time of [[Biology:Epiphyseal plate|epiphyseal (growth) plate]] closure, the legs are more equal in length. Alternatively, a person can be fitted with custom made footwear which corrects the difference in leg lengths. Other surgery to re-balance muscular agonist/antagonist imbalances may also be helpful.  Extended use of braces or wheelchairs may cause [[Medicine:Nerve compression syndrome|compression neuropathy]], as well as a loss of proper function of the [[Medicine:Vein|vein]]s in the legs, due to pooling of blood in paralyzed lower limbs.<ref name= Hoyt>{{cite book |author1=Hoyt, William Graves |author2=Miller, Neil |author3=Walsh, Frank |title=Walsh and Hoyt's clinical neuro-ophthalmology |publisher=Lippincott Williams & Wilkins |location=Hagerstown, MD |year=2005 |pages=3264–65 |isbn=0-7817-4814-3 }}</ref><ref name=MayoComps>{{cite web| author = Mayo Clinic Staff| date = 19 May 2005| url = http://www.mayoclinic.com/health/polio/DS00572/DSECTION=complications| title = Polio: Complications| publisher = Mayo Foundation for Medical Education and Research (MFMER)| accessdate = 26 February 2007| deadurl = no| archiveurl = https://web.archive.org/web/20080623225045/http://www.mayoclinic.com/health/polio/DS00572/DSECTION%3Dcomplications| archivedate = 23 June 2008| df = dmy-all}}</ref> Complications from prolonged immobility involving the lungs, kidneys and [[Biology:Heart|heart]] include [[Medicine:Pulmonary edema|pulmonary edema]], [[Medicine:Aspiration pneumonia|aspiration pneumonia]], [[Medicine:Urinary tract infection|urinary tract infection]]s, kidney stones, paralytic ileus, [[Medicine:Myocarditis|myocarditis]] and cor pulmonale.<ref name= Hoyt/><ref name=MayoComps />

=== Post-polio syndrome ===
{{main|Medicine:Post-polio syndrome}}
Between 25 percent and 50 percent of individuals who have recovered from paralytic polio in childhood can develop additional symptoms decades after recovering from the acute infection,<ref name="NINDS Post-Polio Syndrome Fact Sheet">{{cite web |url=http://www.ninds.nih.gov/disorders/post_polio/detail_post_polio.htm |title=Post-Polio Syndrome Fact Sheet: National Institute of Neurological Disorders and Stroke (NINDS) |work= |accessdate=2 August 2011 |deadurl=yes |archiveurl=https://web.archive.org/web/20110729090555/http://www.ninds.nih.gov/disorders/post_polio/detail_post_polio.htm |archivedate=29 July 2011  }}</ref> notably new muscle weakness and extreme fatigue. This condition is known as [[Medicine:Post-polio syndrome|post-polio syndrome]] (PPS) or post-polio sequelae.<ref name=Cashman>{{cite journal |vauthors=Trojan D, Cashman N |title=Post-poliomyelitis syndrome |journal=Muscle Nerve |volume=31 |issue=1 |pages=6–19 |year=2005 |pmid=15599928 |doi=10.1002/mus.20259}}</ref> The symptoms of PPS are thought to involve a failure of the oversized motor units created during the recovery phase of the paralytic disease.<ref name=Ramlow_1992>{{cite journal |vauthors=Ramlow J, Alexander M, LaPorte R, Kaufmann C, Kuller L |title=Epidemiology of the post-polio syndrome |journal=American Journal of Epidemiology |volume=136 |issue=7 |pages=769–86 |year=1992 |pmid=1442743 |doi=10.1093/aje/136.7.769}}</ref><ref name=Annals>{{cite journal |vauthors=Lin K, Lim Y |title=Post-poliomyelitis syndrome: case report and review of the literature |url=http://www.annals.edu.sg/pdf/34VolNo7200508/V34N7p447.pdf |format=PDF |journal=Annals of the Academy of Medicine, Singapore |volume=34 |issue=7 |pages=447–9 |year=2005 |pmid=16123820 |deadurl=no |archiveurl=https://web.archive.org/web/20070307110123/http://www.annals.edu.sg/pdf/34VolNo7200508/V34N7p447.pdf |archivedate=7 March 2007  }}</ref>  Contributing factors that increase the risk of PPS include aging with loss of neuron units, the presence of a permanent residual impairment after recovery from the acute illness, and both overuse and disuse of neurons. PPS is a slow, progressive disease, and there is no specific treatment for it.<ref name=Cashman /> Post-polio syndrome is not an infectious process, and persons experiencing the syndrome do not shed poliovirus.<ref name="PinkBook2009" />

==Epidemiology==
{| class="wikitable" style="float:right; font-size:85%; margin-left:15px"
| colspan=5 |<center>'''Reported polio cases in 2017'''<ref name="WHO2017Cases">{{cite web|url = http://apps.who.int/immunization_monitoring/en/diseases/poliomyelitis/case_count.cfm|title = Polio Case Count|date = 27 December 2017|accessdate = 27 December 2017|publisher = [[Organization:World Health Organization|World Health Organization]]}}</ref><ref name="PolioThisWeek"/>
[[File:Polio worldwide 2017.svg|center|350px]]
</center>
|-
! Country !! Wild<br />cases !! Circulating<br />vaccine-<br />derived<br />cases !! Transmission<br />status !! Type(s)
|-
|{{flag|Afghanistan}}
|14
|0
|{{color|#f00|endemic}}
|{{color|#f00|WPV1}}
|-
|{{flag|Pakistan}}
|8
|0
|{{color|#f00|endemic}}
|{{color|#f00|WPV1}}
|-
|{{flag|Democratic Republic of the Congo|name=DRC}}
|0
|17
|{{color|#00f|cVDPV only}}
|{{color|#00f|cVDPV2}}
|-
|{{Flag|Syria}}
|0
|74
|{{color|#00f|cVDPV only}}
|{{color|#00f|cVDPV2}}
|-
| '''Total''' ||22||91|| ||
|}

Following the widespread use of poliovirus vaccine in the mid-1950s, the incidence of poliomyelitis declined dramatically in many industrialized countries. A global effort to eradicate polio began in 1988, led by the [[Organization:World Health Organization|World Health Organization]], UNICEF, and The Rotary Foundation.<ref>{{cite web|last1=Vaught|first1=Maureen|title=Polio Vaccine Celebrates 60th Anniversary|url=https://www.rotary.org/en/polio-vaccine-celebrates-60th-anniversary|website=Rotary International|accessdate=11 November 2015|date=10 April 2015|deadurl=no|archiveurl=https://web.archive.org/web/20151117023228/https://www.rotary.org/en/polio-vaccine-celebrates-60th-anniversary|archivedate=17 November 2015}}</ref> These efforts have reduced the number of annual diagnosed cases by 99.9 percent; from an estimated 350,000 cases in 1988 to a low of 483 cases in 2001, after which it remained at a level of about 1,000 – 2000 cases per year for a number of years.<ref name=eradication>{{cite journal |title=Update on vaccine-derived polioviruses |journal=MMWR. Morbidity and Mortality Weekly Report |volume=55 |issue=40 |pages=1093–7 |year=2006 |pmid=17035927 |author1= Centers for Disease Control and Prevention (CDC)}}</ref><ref name=morbidity>{{cite journal |title=Progress toward interruption of wild poliovirus transmission—worldwide, January 2007 – April 2008 |journal=MMWR. Morbidity and Mortality Weekly Report |volume=57 |issue=18 |pages=489–94 |date=May 2008 |pmid=18463607 |doi= |url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5718a4.htm |author=Centers for Disease Control and Prevention (CDC) |deadurl=no |archiveurl=https://web.archive.org/web/20170619054233/https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5718a4.htm |archivedate=19 June 2017  }}</ref> In 2015, cases decreased to 98 and further decreased in 2016 to 37 wild cases and 5 circulating vaccine-derived cases, but increased in 2017 to 22 wild cases and 91 circulating vaccine-derived cases.<ref name="WHO2017Cases"/><ref name="WhoIntCaseCount">{{cite web |url=https://extranet.who.int/polis/public/CaseCount.aspx |title=Archived copy |accessdate=10 January 2015 |deadurl=no |archiveurl=https://web.archive.org/web/20150402165939/https://extranet.who.int/polis/public/CaseCount.aspx |archivedate=2 April 2015  }}</ref><ref name="WHO2015casecount">{{cite web|url = http://apps.who.int/immunization_monitoring/en/diseases/poliomyelitis/case_count.cfm|title = Polio Case Count|date = 18 July 2016|accessdate = 18 July 2016|publisher = [[Organization:World Health Organization|World Health Organization]]|deadurl = no|archiveurl = https://web.archive.org/web/20140816115613/http://apps.who.int/immunization_monitoring/en/diseases/poliomyelitis/case_count.cfm|archivedate = 16 August 2014|df = dmy-all}}</ref><ref>{{cite web|title=Progress Toward Eradication of Polio — Worldwide, January 2011 – March 2013|url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6217a4.htm|website=Centers for Disease Control and Prevention|accessdate=11 November 2015|date=3 May 2013|deadurl=no|archiveurl=https://web.archive.org/web/20151117022756/http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6217a4.htm|archivedate=17 November 2015}}</ref>
Polio is one of only two diseases currently the subject of a global [[Biology:Eradication of infectious diseases|eradication program]], the other being Guinea worm disease.<ref>{{cite web|last1=Akst|first1=Jef|title=Driven to Extinction|url=http://www.the-scientist.com/?articles.view/articleNo/43382/title/Driven-to-Extinction/|website=The Scientist|accessdate=11 November 2015|date=1 July 2015|deadurl=no|archiveurl=https://web.archive.org/web/20151118224852/http://www.the-scientist.com/?articles.view%2FarticleNo%2F43382%2Ftitle%2FDriven-to-Extinction%2F|archivedate=18 November 2015}}</ref> So far, the only diseases completely eradicated by humankind are [[Medicine:Smallpox|smallpox]], declared so, in 1980,<ref name=WHO_smallpox>{{cite web|title=Smallpox |work=WHO Factsheet |url=http://www.who.int/mediacentre/factsheets/smallpox/en/ |accessdate=23 August 2008 |deadurl=yes |archiveurl=https://web.archive.org/web/20070921235036/http://www.who.int/mediacentre/factsheets/smallpox/en/ |archivedate=21 September 2007 |df= }}</ref><ref>{{cite web|title=The Smallpox Eradication Programme – SEP (1966–1980)|url=http://www.who.int/features/2010/smallpox/en/|website=WHO|accessdate=11 November 2015|deadurl=no|archiveurl=https://web.archive.org/web/20151109123858/http://www.who.int/features/2010/smallpox/en/|archivedate=9 November 2015}}</ref> and [[Biology:Rinderpest|rinderpest]], likewise, in 2011.<ref>{{cite web|title=No more deaths from rinderpest|url=http://www.oie.int/for-the-media/press-releases/detail/article/no-more-deaths-from-rinderpest/|website=OIE|accessdate=11 November 2015|date=25 May 2011|deadurl=no|archiveurl=https://web.archive.org/web/20150924072257/http://www.oie.int/for-the-media/press-releases/detail/article/no-more-deaths-from-rinderpest/|archivedate=24 September 2015}}</ref>
A number of eradication milestones have already been reached, and several regions of the world have been certified polio-free.

A concern is the presence of circulating vaccine-derived polioviruses. The oral polio vaccine is not perfect: while the genetic characteristics are carefully balanced to maximize efficacy and minimize virulence, it is possible for the polio virus in the oral vaccine to mutate.  As a result, persons given the oral polio vaccine can acquire acute or chronic infections; or can transmit (circulate) mutated virus to other people. It is likely that circulating vaccine-derived poliovirus cases will exceed wild-type cases in the near future, making it desirable to discontinue use of the oral polio vaccine as soon as safely possible.<ref name="circulating">{{cite web |author1=Olen M. Kew |author2=Peter F. Wright |author3=Vadim I. Agol |author4=Francis Delpeyroux |author5=Hiroyuki Shimizu |author6=Neal Nathanson |author7=Mark A. Pallansch |title=Circulating vaccine-derived polioviruses: current state of knowledge |publisher=Bulletin of the World Health Organization |date=24 October 2003 |url=http://www.scielosp.org/scielo.php?pid=S0042-96862004000100006&script=sci_arttext&tlng=es |accessdate=28 October 2015 |deadurl=no |archiveurl=https://web.archive.org/web/20160304191154/http://www.scielosp.org/scielo.php?pid=S0042-96862004000100006&script=sci_arttext&tlng=es |archivedate=4 March 2016  }}</ref>

In April 2012, the World Health Assembly declared the completion of polio eradication a programmatic emergency for global public health.<ref>{{cite book |author=World Health Assembly |year=2012 |title=Poliomyelitis: intensification of the global eradication initiative. Agenda item A65/20 |url=http://apps.who.int/gb/ebwha/pdf_files/wha65/A65_20-en.pdf |location=Geneva, Switzerland |publisher=World Health Organization |isbn= |accessdate=7 December 2013 |deadurl=no |archiveurl=https://web.archive.org/web/20131109143313/http://apps.who.int/gb/ebwha/pdf_files/WHA65/A65_20-en.pdf |archivedate=9 November 2013  }}</ref>

===Americas===

The [[Earth:Americas|Americas]] were declared polio-free in 1994.<ref name=MMWR_1994>{{cite journal | title = International Notes Certification of Poliomyelitis Eradication—the Americas, 1994 | journal = MMWR. Morbidity and Mortality Weekly Report  | publisher = Centers for Disease Control and Prevention | volume = 43 | issue = 39 | pages = 720–2 | year = 1994 | url = https://www.cdc.gov/mmwr/preview/mmwrhtml/00032760.htm | pmid = 7522302 | author1 = Centers for Disease Control and Prevention (CDC) | deadurl = no | archiveurl = https://web.archive.org/web/20170521163051/https://www.cdc.gov/mmwr/preview/mmwrhtml/00032760.htm | archivedate = 21 May 2017 | df = dmy-all }}</ref>

In June 2018, it was reported that first polio case in Venezuela in 30 years had occurred, in the state of Delta Amacuro.<ref>{{cite web|url=https://www.telegraph.co.uk/news/2018/06/10/venezuela-hit-first-case-polio-since-1989-country-falls-deeper/|title=Venezuela crisis: first case of Polio since 1989 as instability deepens|first=Cody|last=Weddle|date=10 June 2018|publisher=|via=www.telegraph.co.uk}}</ref> Laboratory testing confirmed that the incident was in fact not caused by polio.<ref>{{cite web|url=http://polioeradication.org/news-post/update-on-suspected-polio-case-in-venezuela/|title=GPEI-Update on suspected polio case in Venezuela|website=polioeradication.org}}</ref>

===Western Pacific===

In 2000 polio was declared to have been officially eliminated in 37 Western Pacific countries, including China and Australia.<ref name=Pacific>{{cite journal | author = | title = General News. Major Milestone reached in Global Polio Eradication: Western Pacific Region is certified Polio-Free | journal = Health Education Research | year = 2001 | volume = 16 | issue = 1 | page = 109 | url = http://her.oxfordjournals.org/cgi/reprint/16/1/109.pdf | format = PDF | doi = 10.1093/her/16.1.109 | deadurl = no | archiveurl = https://web.archive.org/web/20070621131041/http://her.oxfordjournals.org/cgi/reprint/16/1/109.pdf | archivedate = 21 June 2007 | df = dmy-all }}</ref><ref name="D'Souza_2002">{{cite journal |vauthors=D'Souza R, Kennett M, Watson C |title=Australia declared polio free |journal=Communicable Diseases Intelligence |volume=26 |issue=2 |pages=253–60 |year=2002 |pmid=12206379}}</ref>

Despite eradication ten years before, an outbreak was confirmed in China in September 2011 involving a strain prevalent in neighboring Pakistan.<ref>{{cite news | url=http://www.cnn.com/2011/09/21/health/china-polio-outbreak/index.html | work=CNN | title=New polio outbreak hits China - CNN.com | date=21 September 2011 | deadurl=no | archiveurl=https://web.archive.org/web/20120101174601/http://www.cnn.com/2011/09/21/health/china-polio-outbreak/index.html | archivedate=1 January 2012 | df=dmy-all }}</ref>

===Europe===

[[Earth:Europe|Europe]] was declared polio-free in 2002.<ref name=WHO_Europe_2002>{{cite press release | title = Europe achieves historic milestone as Region is declared polio-free | publisher = European Region of the World Health Organization | date = 21 June 2002 | url = http://www.who.int/mediacentre/news/releases/releaseeuro02/en/index.html | accessdate = 23 August 2008 | deadurl = no | archiveurl = https://web.archive.org/web/20080916065107/http://www.who.int/mediacentre/news/releases/releaseeuro02/en/index.html | archivedate = 16 September 2008 | df = dmy-all }}</ref> On 1 September 2015, WHO confirmed 2 cases of circulating vaccine-derived poliovirus type 1 in Ukraine.<ref name=WHO_Europe_2015>{{cite web | title = Circulating vaccine-derived poliovirus – Ukraine | publisher = World Health Organization | url = http://www.who.int/csr/don/01-september-2015-polio/en/ | accessdate = 9 September 2015 | date = 1 September 2015 | deadurl = no | archiveurl = https://web.archive.org/web/20150908054032/http://www.who.int/csr/don/01-september-2015-polio/en/ | archivedate = 8 September 2015 | df = dmy-all }}</ref>

===South-East Asia===

The last case of polio in the region was in India in January 2011.<ref>{{cite web| url =http://www.searo.who.int/entity/immunization/topics/polio/eradication/sea-polio-free/en/| title =Polio-free certification: WHO South-East Asia| publisher =WHO| date =27 March 2014| accessdate =27 March 2014| deadurl =no| archiveurl =https://web.archive.org/web/20140327032034/http://www.searo.who.int/entity/immunization/topics/polio/eradication/sea-polio-free/en/| archivedate =27 March 2014| df =dmy-all}}</ref>  Since January 2011, there have been no reported cases of the wild polio infections in India, and in February 2012 the country was taken off the WHO list of polio endemic countries. It was reported that if there are no cases of wild polio in the country for two more years, it would be declared as a polio-free country.<ref>{{cite news|last=Ray|first=Kalyan|title=India wins battle against dreaded polio|newspaper=Deccan Herald|date=26 February 2012}}</ref><ref>{{cite news|title=India polio-free for a year: ‘First time in history we’re able to put up such a map’|url=http://www.telegraphindia.com/1120226/jsp/frontpage/story_15181357.jsp|accessdate=26 February 2012|newspaper=The Telegraph|date=26 February 2012|location=Calcutta, India|deadurl=no|archiveurl=https://web.archive.org/web/20120227220101/http://www.telegraphindia.com/1120226/jsp/frontpage/story_15181357.jsp|archivedate=27 February 2012}}</ref>

On 27 March 2014 the WHO announced the eradication of poliomyelitis in the South-East Asia Region, which includes eleven countries: Bangladesh, Bhutan, North Korea, {{wipe|India}}, Indonesia, [[History:Maldives|Maldives]], Myanmar, Nepal, Sri Lanka, Thailand and Timor-Leste.<ref name="eradication1">{{cite web| url =http://www.searo.who.int/mediacentre/releases/2014/pr1569/en/| title =WHO South-East Asia Region certified polio-free| publisher =WHO| date =27 March 2014| accessdate =27 March 2014| deadurl =no| archiveurl =https://web.archive.org/web/20140327235218/http://www.searo.who.int/mediacentre/releases/2014/pr1569/en/| archivedate =27 March 2014| df =dmy-all}}</ref> With the addition of this region, 80 per cent of the world population lives in polio-free regions.<ref name="eradication1"/>

===Syria===

In 2015, polio was believed to remain [[Medicine:Endemic (epidemiology)|naturally spreading]] in only two countries, {{wipe|Pakistan}} and Afghanistan,<ref name=eradication1/><ref name=GlobalPolio2015>{{cite web|title=Wild poliovirus type 1 and Circulating vaccine-derived poliovirus cases|url=http://www.polioeradication.org/dataandmonitoring/poliothisweek.aspx|website=Global Polio Eradication Initiative|accessdate=26 December 2015|date=23 December 2015|deadurl=no|archiveurl=https://web.archive.org/web/20151224045950/http://www.polioeradication.org/Dataandmonitoring/Poliothisweek.aspx|archivedate=24 December 2015}}</ref><ref>{{cite web |url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6139a4.htm |title=Progress Toward Poliomyelitis Eradication — Afghanistan and Pakistan, January 2011 – August 2012 |date=19 October 2012 |website=CDC |publisher=Centers for Disease Control and Prevention |accessdate=7 December 2013 |deadurl=no |archiveurl=https://web.archive.org/web/20131212113209/http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6139a4.htm |archivedate=12 December 2013  }}</ref><ref>{{cite journal|author=Fine PEM|title=Polio: Measuring the protection that matters most|journal=Journal of Infectious Diseases|year=2009|volume=200|issue=5|pmid=19624277|pages=673–675|doi=10.1086/605331}}</ref> although it continued to cause epidemics in other nearby countries due to hidden or reestablished transmission.<ref>Wild Poliovirus case list 2000-2010; data in WHO/HQ as of 9 November 2010 {{cite web |url=http://www.polioeradication.org/tabid/167/iid/80/Default.aspx |title=Archived copy |accessdate=17 November 2010 |deadurl=yes |archiveurl=https://web.archive.org/web/20101222075237/http://www.polioeradication.org/tabid/167/iid/80/Default.aspx |archivedate=22 December 2010  }}</ref>

In [[Place:Syria|Syria]] difficulties in executing immunization programs in the ongoing civil war led to a return of polio, probably in 2012,<ref>{{cite web|url=https://www.bbc.com/news/magazine-26734465|title=Polio in Syria: An outbreak that threatens the Middle East|work=BBC News|deadurl=no|archiveurl=https://web.archive.org/web/20150703194812/http://www.bbc.com/news/magazine-26734465|archivedate=3 July 2015}}</ref> acknowledged by the WHO in 2013.<ref>{{cite news | url=http://www.dnaindia.com/health/report-syria-polio-cases-spread-to-damascus-and-aleppo-who-1925221 | work=DNA | title=Syria polio cases spread to Damascus and Aleppo – WHO | date=26 November 2013 | accessdate=26 November 2013 | deadurl=no | archiveurl=https://web.archive.org/web/20131128140419/http://www.dnaindia.com/health/report-syria-polio-cases-spread-to-damascus-and-aleppo-who-1925221 | archivedate=28 November 2013 | df=dmy-all }}</ref><ref>{{cite news|url = http://edition.cnn.com/2013/10/29/health/syria-polio/index.html|title = WHO: Polio cases confirmed in Syria|date = 29 October 2013|last = Watkins|first = Tom|newspaper = CNN.com|accessdate = 24 January 2014|deadurl = no|archiveurl = https://web.archive.org/web/20140203121111/http://edition.cnn.com/2013/10/29/health/syria-polio/index.html|archivedate = 3 February 2014|df = dmy-all}}</ref> 15 cases were confirmed among children in [[Place:Syria|Syria]] between October and November 2013 in Deir Ezzor. Later, two more cases, one each in rural [[Place:Damascus|Damascus]] and Aleppo, were identified. It was the first outbreak in Syria since 1999. Doctors and international public health agencies report more than 90 cases of polio in Syria, with fears of contagion in rebel areas from lack of sanitation and safe-water services.<ref name=Suppressed>{{cite journal|last=Sparrow|first=Annie|title=Syria’s Polio Epidemic: The Suppressed Truth|journal=New York Review|date=20 February 2014|url=http://www.nybooks.com/articles/archives/2014/feb/20/syrias-polio-epidemic-suppressed-truth/?insrc=hpma|accessdate=23 January 2014|quote=Ninety or so afflicted children may sound like a small number, but they are only a tiny manifestation of an enormous problem, since for each crippled child up to one thousand more are silently infected. Polio is so contagious that a single case is considered a public health emergency. Ninety cases could mean some 90,000 people infected, each a carrier invisibly spreading the disease to others for weeks on end.|deadurl=no|archiveurl=https://web.archive.org/web/20140125214019/http://www.nybooks.com/articles/archives/2014/feb/20/syrias-polio-epidemic-suppressed-truth/?insrc=hpma|archivedate=25 January 2014}}</ref> In May 2014, the World Health Organization declared polio's renewed spread a world health emergency.<ref name="newscientist.com">{{cite web|url=https://www.newscientist.com/article/dn25518-global-emergency-declared-as-polio-cases-surge.html|title=Global emergency declared as polio cases surge|author=Debora MacKenzie|work=New Scientist|deadurl=no|archiveurl=https://web.archive.org/web/20150426133736/http://www.newscientist.com/article/dn25518-global-emergency-declared-as-polio-cases-surge.html|archivedate=26 April 2015}}</ref><ref name="BBC">{{cite news | url=https://www.bbc.co.uk/news/world-27284389# | title=World facing polio health emergency | work=BBC | date=5 May 2014 | accessdate=5 May 2014 | deadurl=no | archiveurl=https://web.archive.org/web/20140506001219/http://www.bbc.co.uk/news/world-27284389 | archivedate=6 May 2014 | df=dmy-all }}</ref>

A vaccination campaign in Syria operated literally under fire and led to the deaths of several vaccinators,<ref>{{cite web|url=http://news.nationalgeographic.com/2015/03/150305-polio-syria-iraq-islamic-state-refugees-vaccination-virus-jihad/|title=Fighting Polio Amid the Chaos of Syria’s Civil War|author=Photographs Hosam Katan, Reuters|publisher=|deadurl=no|archiveurl=https://web.archive.org/web/20160105100254/http://news.nationalgeographic.com/2015/03/150305-polio-syria-iraq-islamic-state-refugees-vaccination-virus-jihad/|archivedate=5 January 2016}}</ref> but returned vaccination coverage to pre-war levels.<ref>{{cite news | url=https://www.reuters.com/article/2015/01/28/mideast-crisis-syria-polio-idUSL6N0V70ZW20150128 | work=Reuters | first=Sylvia | last=Westall | title=Polio immunisation rate in Syria close to pre-war level -WHO | date=28 January 2015 | deadurl=no | archiveurl=https://web.archive.org/web/20150924212925/http://www.reuters.com/article/2015/01/28/mideast-crisis-syria-polio-idUSL6N0V70ZW20150128 | archivedate=24 September 2015 | df=dmy-all }}</ref> No new cases have been reported since January 2014; vaccination continues, and Iraq is also being closely monitored.<ref>{{cite web|url=http://medicalxpress.com/news/2015-01-polio-cases-syria-year.html|title=No new polio cases in Syria reported for a year: WHO|publisher=|deadurl=no|archiveurl=https://web.archive.org/web/20150804211016/http://medicalxpress.com/news/2015-01-polio-cases-syria-year.html|archivedate=4 August 2015}}</ref><ref>{{cite news | url=http://www.huffingtonpost.com/2015/01/29/polio-vaccines-syria_n_6562368.html | work=Huffington Post | title=WHO: Syria Had Only 1 Recorded Polio Case Last Year | date=29 January 2015 | deadurl=no | archiveurl=https://web.archive.org/web/20150924212152/http://www.huffingtonpost.com/2015/01/29/polio-vaccines-syria_n_6562368.html | archivedate=24 September 2015 | df=dmy-all }}</ref>

===Africa===

In 2003 in northern Nigeria—a country which at that time was considered provisionally polio free—a [[Religion:Fatwa|fatwa]] was issued declaring that the polio vaccine was designed to render children sterile.<ref>{{cite web|url = http://www.unicef.org/cbsc/index_49534.html|title = Polio Eradication Efforts in Nigeria and India|accessdate = 25 December 2013|website = UNICEF|deadurl = no|archiveurl = https://web.archive.org/web/20131225195534/http://www.unicef.org/cbsc/index_49534.html|archivedate = 25 December 2013|df = dmy-all}}</ref> Subsequently, polio reappeared in Nigeria and spread from there to several other countries. In 2013, nine health workers administering polio vaccine were targeted and killed by gunmen on motorcycles in Kano, but this was the only attack.<ref>{{cite web|url=https://www.bbc.co.uk/news/world-africa-21381773|title=Nigeria polio vaccinators shot dead in Kano|work=BBC News|deadurl=no|archiveurl=https://web.archive.org/web/20141228034024/http://www.bbc.co.uk/news/world-africa-21381773|archivedate=28 December 2014}}</ref><ref>{{cite news | url=https://www.bbc.co.uk/news/world-africa-33650543 | work=BBC News | title=Nigeria marks one year without recorded polio case | date=24 July 2015 | deadurl=no | archiveurl=https://web.archive.org/web/20150724162448/http://www.bbc.co.uk/news/world-africa-33650543 | archivedate=24 July 2015 | df=dmy-all }}</ref> Local traditional and religious leaders and polio survivors worked to revive the campaign,<ref name="reuters.com">{{cite news | url=https://www.reuters.com/article/2015/07/23/us-health-polio-nigeria-idUSKCN0PX2RF20150723 | work=Reuters | title=Nigeria marks polio-free year, raising global eradication hopes | date=23 July 2015 | deadurl=no | archiveurl=https://web.archive.org/web/20151119091530/http://www.reuters.com/article/2015/07/23/us-health-polio-nigeria-idUSKCN0PX2RF20150723 | archivedate=19 November 2015 | df=dmy-all }}</ref> and Nigeria has not had a polio case since 24 July 2014. In September 2015, Nigeria was removed from the polio-endemic list.<ref>{{cite news | url=http://www.who.int/mediacentre/news/releases/2015/nigeria-polio/en/ | work=WHO | title=WHO Removes Nigeria from Polio-Endemic List | date=26 September 2015 | accessdate=8 January 2016 | deadurl=no | archiveurl=https://web.archive.org/web/20160119165136/http://www.who.int/mediacentre/news/releases/2015/nigeria-polio/en/ | archivedate=19 January 2016 | df=dmy-all }}</ref>  In 2016 two cases recurred.<ref name=Nigeria2016/>

In 2013 the Center for Disease Control received reports of 183 cases of polio in Somalia, 14 in Kenya and 8 cases in the Somali Region of Ethiopia,<ref name=cdcp>{{cite web|title=Polio in Somalia, Kenya, Ethiopia|url=http://wwwnc.cdc.gov/travel/notices/alert/polio-somalia-kenya|work=22 January 2014|publisher=Centers for Disease Control and Prevention|accessdate=23 January 2014|deadurl=no|archiveurl=https://web.archive.org/web/20140202195113/http://wwwnc.cdc.gov/travel/notices/alert/polio-somalia-kenya|archivedate=2 February 2014}}</ref> but Africa had no confirmed cases of wild poliovirus (WPV) in 2015.<ref name = GlobalPolio2015/> A case of circulating vaccine-derived poliovirus type 2 was detected in Siguiri in Guinea's Kankan region, in August 2014.<ref name="gpe2015">{{cite news|url=http://www.polioeradication.org/mediaroom/newsstories/Circulating-vaccine-derived-poliovirus-in-Mali-/tabid/526/news/1280/Default.aspx|title=Circulating vaccine-derived poliovirus in Mali|work=The Global Polio Eradication Initiative|accessdate=9 September 2015|date=9 September 2015|deadurl=yes|archiveurl=https://web.archive.org/web/20150914022123/http://www.polioeradication.org/mediaroom/newsstories/Circulating-vaccine-derived-poliovirus-in-Mali-/tabid/526/news/1280/Default.aspx|archivedate=14 September 2015}}</ref> In September 2015, a case of circulating vaccine-derived poliovirus in Mali was confirmed by the WHO.<ref name=gpe2015 /> In 2017, it was reported that separate new outbreaks caused by circulating vaccine-derived poliovirus type 2 had occurred in southern and east-central provinces in the Democratic Republic of the Congo.<ref>{{cite web|last=Herriman|first=Robert|title=Polio update: Two circulating vaccine-derived poliovirus type 2 outbreaks reported in Democratic Republic of the Congo|publisher=Outbreak News Today|url=http://outbreaknewstoday.com/polio-update-two-cvdpv2-outbreaks-reported-democratic-republic-congo-39590/|date=25 May 2017|accessdate=25 May 2017|deadurl=no|archiveurl=https://web.archive.org/web/20170525194827/http://outbreaknewstoday.com/polio-update-two-cvdpv2-outbreaks-reported-democratic-republic-congo-39590/|archivedate=25 May 2017}}</ref>

===Afghanistan and Pakistan===

This is the last remaining region with wild polio cases. Both major sides of the Afghan civil war support polio vaccination<ref>{{cite news | url=https://www.bbc.co.uk/news/world-asia-26121732 | work=BBC News | title=Afghanistan polio: First case in Kabul since 2001 | date=11 February 2014 | deadurl=no | archiveurl=https://web.archive.org/web/20150409175500/http://www.bbc.co.uk/news/world-asia-26121732 | archivedate=9 April 2015 | df=dmy-all }}</ref> and polio rates are declining rapidly in Afghanistan, with 19 cases in 2015<ref name = GlobalPolio2015/><ref name="reuters.com"/> and 13 in 2016.<ref name="cases2016">{{cite news|title=Polio in Afghanistan: 'Americans bomb our children daily, why would they care?'|url=https://www.theguardian.com/global-development/2017/apr/10/polio-afghanistan-taliban-health-chief-americans-bomb-children|author=Sune Engel Rasmussen|date=10 April 2017|publisher=The Guardian|deadurl=no|archiveurl=https://web.archive.org/web/20170412093358/https://www.theguardian.com/global-development/2017/apr/10/polio-afghanistan-taliban-health-chief-americans-bomb-children|archivedate=12 April 2017}}</ref>

In {{wipe|Pakistan}} there were 53 cases in 2015, the highest number for any country,<ref name = GlobalPolio2015/><ref name="reuters.com"/> and 20 in 2016.<ref name="cases2016"/> Vaccination in Pakistan is hindered by conflict and organizational problems. The militant [[Religion:Tehrik-i-Taliban Pakistan|Pakistani Taliban]] claims vaccination is a Western plot to sterilise local children.<ref name=BBC2016/> 66 vaccinators were killed in 2013 and 2014.<ref>{{cite web|url=http://www.thenational.ae/world/south-asia/pakistans-fight-against-polio-clashes-with-battle-against-taliban#page2|title=Pakistan's fight against polio clashes with battle against Taliban – The National|author=Taimur Khan|publisher=|deadurl=no|archiveurl=https://web.archive.org/web/20150928122419/http://www.thenational.ae/world/south-asia/pakistans-fight-against-polio-clashes-with-battle-against-taliban#page2|archivedate=28 September 2015}}</ref><ref name="thenational.ae">{{cite web|url=http://www.thenational.ae/uae/health/uae-polio-campaign-vaccinates-millions-of-pakistani-children|title=UAE polio campaign vaccinates millions of Pakistani children|author=The National staff|publisher=|deadurl=no|archiveurl=https://web.archive.org/web/20150910053250/http://www.thenational.ae/uae/health/uae-polio-campaign-vaccinates-millions-of-pakistani-children|archivedate=10 September 2015}}</ref> Cases have dropped by 70 percent in 2015; reasons include Dh440 million support from the [[Place:United Arab Emirates|United Arab Emirates]] to vaccinate more than ten million children,<ref name="thenational.ae"/><ref>{{cite web|url=http://www.thenational.ae/uae/health/17-million-children-to-be-vaccinated-against-polio-in-pakistan|title=17 million children to be vaccinated against polio in Pakistan|author=The National staff|publisher=|deadurl=no|archiveurl=https://web.archive.org/web/20150910054826/http://www.thenational.ae/uae/health/17-million-children-to-be-vaccinated-against-polio-in-pakistan|archivedate=10 September 2015}}</ref> changes in the military situation, and arrests of some of those who attacked polio workers.<ref name=BBC2016>{{Cite web|url=https://www.bbc.co.uk/news/world-asia-36300034|title=Pakistan could beat polio in months, says WHO|date=16 May 2016|website=BBC News|access-date=16 May 2016|deadurl=no|archiveurl=https://web.archive.org/web/20160516114003/http://www.bbc.co.uk/news/world-asia-36300034|archivedate=16 May 2016}}</ref><ref>{{cite web|url=https://www.bbc.com/news/world-asia-32996624|title=Polio in Pakistan: Drop of 70% recorded this year|work=BBC News|deadurl=no|archiveurl=https://web.archive.org/web/20150604035928/http://www.bbc.com/news/world-asia-32996624|archivedate=4 June 2015}}</ref>

== History ==
[[File:Polio Egyptian Stele.jpg|thumb|left|An [[Place:Egypt|Egypt]]ian [[Stele|stele]] thought to represent a polio victim, 18th Dynasty (1403–1365 BC)]]

The effects of polio have been known since [[History:Prehistory|prehistory]]; Egyptian paintings and carvings depict otherwise healthy people with withered limbs, and children walking with canes at a young age.<ref name=Paul_1971>{{cite book| author = Paul JR| title=A History of Poliomyelitis| publisher=Yale University Press| location= New Haven, Conn| year=1971| pages=16–18| isbn= 0-300-01324-8| series= Yale studies in the history of science and medicine}}</ref>  The first clinical description was provided by the English physician Michael Underwood in 1789, where he refers to polio as "a debility of the lower extremities".<ref name=Underwood_1789>{{cite book | last = Underwood | first = Michael | chapter = Debility of the lower extremities|title=A treatise on the diseases of children, with general directions for the management of infants from the birth (1789) | volume = 2 | publisher = J. Mathews | location=London | year = 1789 | pages = 88–91 | chapter-url=https://archive.org/stream/b21516728_0002#page/n103/mode/2up}}</ref> The work of physicians Jakob Heine in 1840 and Karl Oskar Medin in 1890 led to it being known as ''Heine–Medin disease''.<ref name=Pearce_2005>{{cite journal |author=Pearce J |title=Poliomyelitis (Heine-Medin disease) |journal=Journal of Neurology, Neurosurgery, and Psychiatry |volume=76 |issue=1 |page=128 |year=2005 |doi=10.1136/jnnp.2003.028548 | pmid=15608013 |pmc=1739337}}</ref> The disease was later called ''infantile paralysis'', based on its propensity to affect children.

Before the 20th century, polio infections were rarely seen in infants before six months of age, most cases occurring in children six months to four years of age. Poorer [[Engineering:Sanitation|sanitation]] of the time resulted in a constant exposure to the virus, which enhanced a natural [[Medicine:Immunity (medical)|immunity]] within the population. In developed countries during the late 19th and early 20th centuries, improvements were made in community sanitation, including better [[Earth:Sewage|sewage]] disposal and clean water supplies. These changes drastically increased the proportion of children and adults at risk of paralytic polio infection, by reducing childhood exposure and immunity to the disease.<ref name="Robertson_1993">{{cite web | author = Robertson S | title = Module 6: Poliomyelitis | work = The Immunological Basis for Immunization Series | publisher = World Health Organization. Geneva, Switzerland. | url = http://whqlibdoc.who.int/hq/1993/WHO_EPI_GEN_93.16_mod6.pdf?ua=1 | format = PDF | year = 1993 | accessdate = 23 August 2008 | deadurl = no | archiveurl = https://web.archive.org/web/20140202115733/http://whqlibdoc.who.int/hq/1993/WHO_EPI_GEN_93.16_mod6.pdf?ua=1 | archivedate = 2 February 2014 | df = dmy-all }}</ref>

Small localized paralytic polio [[Medicine:Epidemic|epidemic]]s began to appear in Europe and the United States around 1900.<ref name = Trevelyan>{{cite journal |vauthors=Trevelyan B, Smallman-Raynor M, Cliff A |title=The Spatial Dynamics of Poliomyelitis in the United States: From Epidemic Emergence to Vaccine-Induced Retreat, 1910–1971 |pmc=1473032 |journal=Annals of the Association of American Geographers |volume=95 |issue=2 |pages=269–93 |year=2005 |pmid=16741562 |doi=10.1111/j.1467-8306.2005.00460.x}}</ref> Outbreaks reached [[Finance:Pandemic|pandemic]] proportions in Europe, North America, Australia, and New Zealand during the first half of the 20th century. By 1950, the peak age incidence of paralytic poliomyelitis in the United States had shifted from infants to children aged five to nine years, when the risk of paralysis is greater; about one-third of the cases were reported in persons over 15 years of age.<ref name=Melnick_1990>{{cite book | author = Melnick JL | title = Poliomyelitis. In: Tropical and Geographical Medicine | edition = 2nd | publisher = McGraw-Hill | year =1990 | pages = 558–76 | isbn = 0-07-068328-X }}</ref> Accordingly, the rate of paralysis and death due to polio infection also increased during this time.<ref name = Trevelyan/> In the United States, the 1952 polio epidemic became the worst outbreak in the nation's history.  Of the nearly 58,000 cases reported that year, 3,145 died and 21,269 were left with mild to disabling paralysis.<ref name="Zamula">{{cite journal |author = Zamula E |title = A New Challenge for Former Polio Patients |url = https://www.questia.com/library/1G1-10942759/a-new-challenge-for-former-polio-patients |journal = FDA Consumer |volume = 25 |issue = 5 |pages = 21–5 |year = 1991 |deadurl = no |archiveurl = https://web.archive.org/web/20140220034400/http://www.questia.com/library/1G1-10942759/a-new-challenge-for-former-polio-patients |archivedate = 20 February 2014 |df = dmy-all }}</ref> [[Medicine:Intensive care medicine|Intensive care medicine]] has its origin in the fight against polio.<ref>{{cite web|url=https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B7CdB217pf6yN2QxOGI5NTUtZWIzYS00N2NhLWFhODQtOGZjMjdhZTlkZGE5&hl=de |title= Louise Reisner-Sénélar (2009) The Danish anaesthesiologist Björn Ibsen a pioneer of long-term ventilation on the upper airways}}</ref> Most hospitals in the 1950s had limited access to [[Engineering:Iron lung|iron lung]]s for patients unable to breathe without mechanical assistance. Respiratory centers designed to assist the most severe polio patients, first established in 1952 at the Blegdam Hospital of [[Place:Copenhagen|Copenhagen]] by {{wipe|Denmark}} [[Medicine:Anesthesia|anesthesiologist]] [[Biography:Bjørn Aage Ibsen|Bjørn Ibsen]], were the harbingers of subsequent [[Medicine:Intensive care unit|intensive care unit]]s (ICU). (A year later, Ibsen would establish the world's first dedicated ICU.)<ref>{{cite journal|author=Pincock S |title=Bjørn Aage Ibsen|journal=The Lancet|editor=Elsevier|year=2007|volume=370|issue=9598|page=1538|doi=10.1016/S0140-6736(07)61650-X|url=http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(07)61650-X/fulltext?version=printerFriendly}}</ref>

The polio epidemics not only altered the lives of those who survived them, but also brought profound cultural changes, spurring [[Social:Grassroots|grassroots]] fund-raising campaigns that would revolutionize medical philanthropy, and giving rise to the modern field of [[Medicine:Physical therapy|rehabilitation therapy]]. As one of the largest disabled groups in the world, polio survivors also helped to advance the modern disability rights movement through campaigns for the social and civil rights of the disabled. The World Health Organization estimates that there are 10 to 20 million polio survivors worldwide.<ref name=NewsDesk>{{cite web | title = After Effects of Polio Can Harm Survivors 40 Years Later | publisher = March of Dimes | url = http://www.marchofdimes.org/news/after-effects-of-polio-can-harm-survivors-40-years-later.aspx | date = 1 June 2001 | accessdate = 14 November 2014 | deadurl = no | archiveurl = https://web.archive.org/web/20141225210413/http://www.marchofdimes.org/news/after-effects-of-polio-can-harm-survivors-40-years-later.aspx | archivedate = 25 December 2014 | df = dmy-all }}</ref> In 1977 there were 254,000 persons living in the United States who had been paralyzed by polio.<ref>{{cite journal |vauthors=Frick NM, Bruno RL | title = Post-polio sequelae: physiological and psychological overview | journal = Rehabilitation Literature | volume = 47 | issue = 5–6 | pages = 106–11 | year = 1986 | pmid = 3749588 }}</ref> According to doctors and local polio support groups, some 40,000 polio survivors with varying degrees of paralysis live in Germany, 30,000 in Japan, 24,000 in France, 16,000 in Australia, 12,000 in Canada and 12,000 in the United Kingdom.<ref name= NewsDesk/> Many notable individuals have survived polio and often credit the prolonged immobility and residual paralysis associated with polio as a driving force in their lives and careers.<ref>{{cite book |author=Richard L. Bruno |title=The Polio Paradox: Understanding and Treating "Post-Polio Syndrome" and Chronic Fatigue |publisher=Warner Books |location=New York |year=2002 |pages= 105–6|isbn=0-446-69069-4 }}</ref>

The disease was very well publicized during the polio epidemics of the 1950s, with extensive media coverage of any scientific advancements that might lead to a cure. Thus, the scientists working on polio became some of the most famous of the century. Fifteen scientists and two laymen who made important contributions to the knowledge and treatment of poliomyelitis are honored by the Polio Hall of Fame, which was dedicated in 1957 at the Roosevelt Warm Springs Institute for Rehabilitation in Warm Springs, Georgia, US. In 2008 four organizations (Rotary International, the World Health Organization, the U.S. Centers for Disease Control and UNICEF) were added to the Hall of Fame.<ref>{{cite news | first=Winston | last=Skinner | title=Four added to Polio Hall of Fame at Warm Springs | date=15 November 2008 | publisher= | url=http://www.times-herald.com/Local/Four-added-to-Polio-Hall-of-Fame-at-Warm-Springs-589785 | work=The Times-Herald (Newnan, GA) | pages= | accessdate=29 May 2009 | deadurl=yes | archiveurl=https://web.archive.org/web/20100328073707/http://www.times-herald.com/Local/Four-added-to-Polio-Hall-of-Fame-at-Warm-Springs-589785 | archivedate=28 March 2010 | df=dmy-all }}</ref><ref>{{cite news | title=CDC Inducted into Polio Hall of Fame | date=23 January 2009 | publisher= | url =https://www.cdc.gov/news/2009/01/polio_hof/ | work =CDC In the News | pages = | accessdate = |archiveurl=https://web.archive.org/web/20150924132112/https://www.cdc.gov/news/2009/01/polio_hof/|archivedate=24 September 2015}}</ref>

World Polio Day (24 October) was established by Rotary International to commemorate the birth of Jonas Salk, who led the first team to develop a vaccine against poliomyelitis. Use of this inactivated poliovirus vaccine and subsequent widespread use of the oral poliovirus vaccine developed by Albert Sabin led to establishment of the [[Organization:Global Polio Eradication Initiative|Global Polio Eradication Initiative]] (GPEI) in 1988. Since then, GPEI has reduced polio worldwide by 99 percent.<ref>{{cite web |url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6141a6.htm |title=Announcement: World Polio Day — 24 October 2012 |date=19 October 2012 |website=CDC |publisher=Centers for Disease Control and Prevention |accessdate=7 December 2013 |deadurl=no |archiveurl=https://web.archive.org/web/20131212113105/http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6141a6.htm |archivedate=12 December 2013  }}</ref>

===Etymology===
The term derives from the [[Social:Ancient Greek|Ancient Greek]] {{transl|grc|''poliós''}} ({{lang|grc|πολιός}}), meaning "grey", {{transl|grc|''myelós''}} ({{lang|grc|µυελός}} “marrow”), referring to the grey matter of the [[Biology:Spinal cord|spinal cord]], and the suffix ''-itis'', which denotes [[Medicine:Inflammation|inflammation]],<ref name=Chamberlin_2005>{{cite book | veditors = Chamberlin SL, Narins B | title = The Gale Encyclopedia of Neurological Disorders | publisher = Thomson Gale | location = Detroit | year = 2005 | pages = 1859–70| isbn = 0-7876-9150-X}}</ref> i.e., inflammation of the spinal cord’s grey matter, although a severe infection can extend into the brainstem and even higher structures, resulting in polio''encephal''itis, producing a lack of ability to breathe that requires mechanical assistance such as an [[Engineering:Iron lung|iron lung]].

==Research==
The Poliovirus Antivirals Initiative was launched in 2007 with the aim of developing antiviral medications for polio, but while several promising candidates were identified, none have progressed beyond Phase II clinical trials.<ref>{{cite journal|last1=Thibaut|first1=HJ|last2=De Palma|first2=AM|last3=Neyts|first3=J|title=Combating enterovirus replication: state-of-the-art on antiviral research.|journal=Biochemical Pharmacology|date=15 January 2012|volume=83|issue=2|pages=185–92|pmid=21889497|doi=10.1016/j.bcp.2011.08.016}}</ref><ref>{{cite journal|last1=McKinlay|first1=MA|last2=Collett|first2=MS|last3=Hincks|first3=JR|last4=Oberste|first4=MS|last5=Pallansch|first5=MA|last6=Okayasu|first6=H|last7=Sutter|first7=RW|last8=Modlin|first8=JF|last9=Dowdle|first9=WR|title=Progress in the development of poliovirus antiviral agents and their essential role in reducing risks that threaten eradication.|journal=Journal of Infectious Diseases|date=1 November 2014|volume=210 Suppl 1|pages=S447-53|pmid=25316866|doi=10.1093/infdis/jiu043}}</ref>

==See also==
*[[Medicine:Poliomyelitis eradication|Poliomyelitis eradication]]
*[[Engineering:Polio vaccine|Polio vaccine]]
*Social Mobilisation Network (SMNet)

== References ==
{{Reflist}}

== Further reading ==
* {{cite book|author = Kluger Jefferey|title=Splendid Solution - Jonas Salk and the Conquest of Polio |url= https://books.google.com/?id=PE6rXNMlwmkC&printsec=frontcover&dq=Splendid+Solution+-+Jonas+Salk+and+the+Conquest+of+Polio&cd=1#v=onepage&q |publisher=G. P. Putnam's Sons|location=New York |year=2004 |pages= |isbn=0-399-15216-4 }}
* {{cite book |author=Oshinsky, David M. |title=Polio: an American story |publisher=Oxford University Press |location=Oxford |year=2005 |pages= |isbn=0-19-515294-8 |url= https://books.google.com/?id=cTliwSU62KIC&printsec=frontcover&dq=polio&cd=2#v=onepage&q |oclc= |doi= |accessdate=}}
* {{cite book |author1=Shaffer, Mary M. |author2=Bernard Seytre |title=The death of a disease: a history of the eradication of poliomyelitis |publisher=Rutgers University Press |location=New Brunswick, N.J |year=2005 |pages= |isbn=0-8135-3677-4 |url= https://books.google.com/?id=iKidtL80imMC&printsec=frontcover&dq=polio&q=polio |oclc= |doi= |accessdate=}}
* {{cite book |author=Shell, Marc |title=Polio and its aftermath: the paralysis of culture |publisher=Harvard University Press |location=Cambridge |year=2005 |pages= |isbn=0-674-01315-8 |url= https://books.google.com/?id=yk40sRCHF7IC&printsec=frontcover&dq=polio&cd=50#v=onepage&q |oclc= |doi= |accessdate=}}
* {{cite book |author=Wilson, Daniel J. |title=Living with polio: the epidemic and its survivors |publisher=University of Chicago Press |location=Chicago |year=2005 |pages= |isbn=0-226-90103-3 |url= https://books.google.com/?id=Ejvjfo_K-IQC&printsec=frontcover&dq=polio&cd=3#v=onepage&q |oclc= |doi= |accessdate=}}
* {{cite book |author1=Wilson, Daniel J. |author2=Julie Silver |title=Polio voices: an oral history from the American polio epidemics and worldwide eradication efforts |publisher=Praeger |location=New York |year=2007 |pages= |isbn=0-275-99492-9 |url= https://books.google.com/?id=RomvGee67tUC&printsec=frontcover&dq=polio&cd=13&q |oclc= |doi= |accessdate=}}

== External links ==
* {{dmoz|Health/Conditions_and_Diseases/Infectious_Diseases/Viral/Poliomyelitis/}}
{{Medical condition classification and resources

|ICD10          = {{ICD10|A|80||a|80}}, {{ICD10|B|91||b|90}}, {{ICD10|P|35.8||p|35}}
|ICD9           = {{ICD9|045}}, {{ICD9|138}}
|DiseasesDB     = 10209
|MedlinePlus    = 001402
|eMedicineSubj  = ped
|eMedicineTopic = 1843
|eMedicine_mult = {{eMedicine2|pmr|6}}
|MeshName       = Poliomyelitis
|MeshNumber     = C02.182.600.700
}}


{{Viral diseases}}
{{CNS diseases of the nervous system}}


[[Category:RTTID]]

{{Sourceattribution|Poliomyelitis|1}}