View source for Poliomyelitis

{{DiseaseDisorder infobox |
  Name        = Poliomyelitis |
  Image       = Polio lores134.jpg|
  Image caption = A man with an [[Atrophy|atrophied]] right leg due to poliomyelitis.|
  ICD10       = {{ICD10|A|80||a|80}}, {{ICD10|B|91||b|90}} |
  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 |
}}
{{SI}}
{{CMG}}

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{{otheruses4|the disease|the virus which causes poliomyelitis|Poliovirus}}

==Overview==
'''Poliomyelitis''' (from the [[Greek language|Greek]] ''polio'' (πολίός), meaning ''gray'', ''myelon'' (µυЄλός), referring to the [[spinal cord]], and ''[[-itis]]'' denotes [[inflammation]]<ref name=Chamberlin_2005>{{cite book | author = Chamberlin SL, Narins B (eds.) | title = The Gale Encyclopedia of Neurological Disorders | publisher = Thomson Gale | location = Detroit | year = 2005 | pages = | isbn = 0-7876-9150-X}}</ref>) often called '''polio''' or '''infantile paralysis''', is an acute [[virus (biology)|viral]] [[infectious disease]] spread from person-to-person, primarily via the [[fecal-oral route]].<ref name=Harrison>{{cite book | author = Cohen JI | chapter = Chapter 175: Enteroviruses and Reoviruses | title = Harrison's Principles of Internal Medicine | editor = Kasper DL, Braunwald E, Fauci AS, ''et al'' (eds.)| edition = 16th ed. | publisher = McGraw-Hill Professional | year = 2004 | pages = 1144 | isbn = 0071402357 }}</ref> While roughly 90% of polio infections are [[asymptomatic]], affected individuals can exhibit a range of more severe symptoms if the virus enters the [[Blood|blood stream]].<ref name=Sherris>{{cite book | author = Ryan KJ, Ray CG (eds.) | chapter = Enteroviruses | title = Sherris Medical Microbiology | edition = 4th ed. | pages = 535–7 | publisher = McGraw Hill | year = 2004 | id = ISBN 0-8385-8529-9 }}</ref> In less than 1% of polio cases the virus enters the [[central nervous system]] (CNS), preferentially infecting and destroying [[motor neuron]]s.<ref name = PinkBook>{{cite book | author = Atkinson W, Hamborsky J, McIntyre L, Wolfe S (eds.) | chapter = Poliomyelitis. | title = Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book)  | edition = 10th ed. | pages = 101&ndash;14 | publisher = Public Health Foundation | location =Washington DC |year = 2007 | url = http://www.cdc.gov/vaccines/pubs/pinkbook/downloads/polio.pdf | format = PDF}}</ref> The destruction of motor neurons causes [[muscle]] weakness and ''[[Flaccid paralysis|acute flaccid paralysis]]''.

While polio-like symptoms have been identified in ancient cultures [[wiktionary:retrospective|retrospectively]], poliomyelitis was first recognized as a distinct condition by [[Jakob Heine]] in 1840.<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= |isbn=0-300-01324-8 | series = Yale studies in the history of science and medicine}}</ref> In the early 20th century much of the world experienced a dramatic increase in the number of polio cases, leading to a series of [[epidemic]]s. These epidemics&mdash;which left thousands of children and adults paralyzed&mdash;provided the impetus for a "Great Race" towards the development of an effective [[vaccine]]. The development of [[polio vaccine]]s by [[Jonas Salk]] (1952) and [[Albert Sabin]] (1962), are credited with reducing of the annual number of polio cases from many hundreds of thousands to around a thousand today.<ref name=Aylward_2006>{{cite journal |author=Aylward R |title=Eradicating polio: today's challenges and tomorrow's legacy |journal=Ann Trop Med Parasitol |volume=100 |issue=5-6 |pages=401-13 |year=2006 |pmid=16899145}}</ref> Recently, enhanced [[vaccination]] efforts led by the [[World Health Organization]], UNICEF and Rotary International may soon result in global eradication of the disease.<ref>{{cite journal |author=Heymann D |title=Global polio eradication initiative | url=http://www.scielosp.org/scielo.php?script=sci_arttext&pid=S0042-96862006000800006&lng=en&nrm=iso&tlng=en |journal=Bull. World Health Organ. |volume=84 |issue=8 |pages=595 |year=2006 |pmid=16917643 |doi=}}</ref>

==Cause==

[[Image:Polio EM PHIL 1875 lores.PNG|thumb|left|A [[Transmission electron microscopy|TEM]] [[micrograph]] of poliovirus.]]
{{main|Poliovirus}}
Poliomyelitis is caused by infection with [[poliovirus]], a human [[pathogen]] which cannot naturally infect other species.<ref name=Sherris />  A [[RNA virus|small RNA]] [[enterovirus]],<ref name=Harrison /> poliovirus is structurally very simple; it is composed of an [[RNA]] [[genome]] enclosed in a non-[[Viral envelope|enveloped]] [[capsid]].<ref name=Sherris />  There are three different [[serotype]]s of poliovirus, poliovirus type 1 (PV1), type 2 (PV2), and type 3 (PV3), each with a slightly different capsid protein. All three forms are extremely [[virulence|virulent]] and produce the same disease symptoms.<ref name=Sherris /> PV1 is the most commonly encountered form.

==Transmission==

Poliomyelitis is a highly contagious disease which spreads easily via human-to-human contact.<ref name=Kew_2005>{{cite journal |author=Kew O, Sutter R, de Gourville E, Dowdle W, Pallansch M |title=Vaccine-derived polioviruses and the endgame strategy for global polio eradication |journal=Annu Rev Microbiol |volume=59 |issue= |pages=587-635 |year=2005 |pmid=16153180}}</ref> In [[endemic]] areas wild polioviruses can infect virtually the entire human population.<ref name=McGraw>{{cite book |author = Parker SP (ed.) | title = McGraw-Hill Concise Encyclopedia of Science & Technology |publisher=McGraw-Hill |location=New York |year=1998 | isbn=0-07-052659-1}}</ref> In temperate climates poliomyelitis is a seasonal disease, with periods of peak transmission in the summer and autumn and reduced levels during winter.<ref name=Kew_2005 /> In tropical areas seasonal differences in transmission are far less pronounced.<ref name=McGraw />

The incubation period of polio, from the time of first exposure to first symptoms, is 2-20 days, with a range of 3 to 35 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}}</ref> Following the initial poliovirus infection, virus particles are excreted in the [[feces]] for several weeks.<ref name=Racaniello /> The infection is [[Transmission (medicine)|transmitted]] via the [[fecal-oral route]]: poor hand washing allows the virus to remain on the hands after eating or using the bathroom. While the risk of transmission is highest seven to 10 days before and after the onset of symptoms, transmission is possible as long as the virus remains in the throat or feces.<ref name=Chamberlin_2005 />

Factors which increase the risk of polio infection or affect the severity of the disease include [[immune deficiency]],<ref>{{cite journal |author=Davis L, Bodian D, Price D, Butler I, Vickers J |title=Chronic progressive poliomyelitis secondary to vaccination of an immunodeficient child |journal=N Engl J Med |volume=297 |issue=5 |pages=241-5 |year=1977 |pmid = 195206}}</ref> [[malnutrition]],<ref>{{cite journal |author=Chandra R |title=Reduced secretory antibody response to live attenuated measles and poliovirus vaccines in malnourished children| url= http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=1131622|journal=Br Med J |volume=2 |issue=5971 |pages=583-5 |year=1975 |pmid=1131622}}</ref> [[tonsillectomy]],<ref>{{cite journal |author=Miller A |title=Incidence of poliomyelitis; the effect of tonsillectomy and other operations on the nose and throat | url= http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=12978882 |journal=Calif Med |volume=77 |issue=1 |pages=19-21 |year=1952 |pmid=12978882}}</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=J Am Med Assoc |volume=142 |issue=4 |pages=236-41 |year=1950 |pmid=15400610}}</ref> [[intramuscular injection]],<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=Bacteriol Rev |volume=24 |issue=4 |pages=341-52 |year=1960 |pmid=13697553}}</ref> and [[pregnancy]].<ref name=Evans_1960 /> During pregnancy, the virus can cross the [[placenta]], however it does not appear that the fetus is affected by either maternal infection with wild poliovirus, or by polio vaccination.<ref name=UK>{{cite book |author=Joint Committee on Vaccination and Immunisation (Salisbury A, Ramsay M, Noakes K (eds.) |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 = 313-329 |isbn = 0-11-322528-8}}</ref> Maternal [[antibodies]] to poliovirus are able to cross the [[placenta]], providing [[passive immunity]]  that protects the infant from polio infection during the first few months of life.<ref>{{cite journal |author=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=Med Microbiol Immunol |volume=190 |issue=4 |pages=167-72 |year=2002 |pmid=12005329}}</ref>

== Classification ==

{| class = "prettytable" style = "float:right; font-size:90%; margin-left:15px"
|+'''Forms of poliomyelitis'''
|-
! style="background:#efefef;" | Form
! style="background:#efefef" | Proportion of cases<ref name = PinkBook/>
|-
| Asymptomatic
| align="center" |90-95%
|-
| Minor illness
|align="center" |4-8%
|-
|Non-paralytic aseptic<br/> meningitis
| align="center" |1-2%
|-
|Paralytic poliomyelitis
| align="center" |0.1-0.5%
|-
|— Spinal Polio
|align="center" |79% of paralytic cases
|-
|— Bulbospinal Polio
|align="center" |19% of paralytic cases
|-
|— Bulbar Polio
|align="center" |2% of paralytic cases
|}

The term "poliomyelitis" is used to identify all conditions caused by any of three poliovirus [[serotype]]s. During the acute polio epidemics in the early 20th century, several categories of poliomyelitis were defined to classify the extent and seriousness of the disease.<ref>{{cite journal |author=Falconer M, Bollenbach E |title=Late functional loss in nonparalytic polio |journal=American journal of physical medicine & rehabilitation / Association of Academic Physiatrists |volume=79 |issue=1 |pages=19-23 |year=2000 |pmid=10678598}}</ref> Two basic patterns of polio infection are described:<!-- still current? --> a minor illness which does not involve the [[central nervous system]] (CNS), sometimes called ''abortive polio'', and a major illness involving the CNS, which may be paralytic or non-paralytic.  

In the majority of [[immunocompetent]] individuals (those with a normal [[immune system]]), a poliovirus infection is abortive, producing either no&ndash; or minor symptoms such as upper [[respiratory tract]] infection (sore throat and fever), [[gastrointestinal tract]] disturbances (nausea, vomiting, abdominal pain, constipation or, rarely, diarrhea), and [[influenza]]-like illnesses.<ref name=Baron>{{cite book | author =  Yin-Murphy M, Almond JW | chapter = Picornaviruses: The Enteroviruses: Polioviruses | title = Baron's Medical Microbiology'' (Baron S ''et al'', eds.)| edition = 4th ed. | publisher = Univ of Texas Medical Branch | year = 1996 | url= http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.2862 | isbn = 0-9631172-1-1 }}</ref>

In about 3% of poliovirus infections, the virus enters the [[central nervous system]]. In 1–2% of infections patients develop non-paralytic [[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/ | publisher=Commonwealth Department of Community Services and Health |year = 1992 |isbn=1-875412-05-0}}</ref>  

In approximately 1 in 200 to 1 in 1000 cases, poliovirus infection leads to the development of [[paralytic]] disease, in which the muscles become weak, floppy and poorly-controlled, and finally completely paralyzed; this condition is known as ''[[Flaccid paralysis|acute flaccid paralysis]]'' (AFP).<ref name=Henry1 />  Depending on the site of paralysis, paralytic poliomyelitis is classified as ''spinal'', ''bulbar'', or ''bulbospinal''.

In rare cases, [[encephalitis]] (an infection of the brain tissue itself) can occur. This form is usually restricted to infants and is characterized by confusion, changes in mental status, headaches, and fever; [[seizure]]s and [[spastic paralysis]] may also occur.<ref name= Encephalitis>{{cite book |author=Wood, Lawrence D. H.; Hall, Jesse B.; Schmidt, Gregory D. |title=Principles of Critical Care, Third Edition |publisher=McGraw-Hill Professional |location= |year=2005 |pages=870 |isbn=0-07-141640-4 |oclc= |doi=}}</ref>

== Mechanism ==
[[Image: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 it comes into contact with&mdash;[[follicular dendritic cell]]s residing within the [[germinal center]]s of the [[tonsils]] and intestinal [[M cell]]s&mdash;by binding to a [[Immunoglobulin|immunoglobulin-like]] receptor known as the ''poliovirus receptor'' ([[CD155]]) on the cell surface.<ref name=He>{{cite journal |author=He Y, Mueller S, Chipman P, ''et al'' |title=Complexes of poliovirus serotypes with their common cellular receptor, CD155 | url= http://jvi.asm.org/cgi/content/full/77/8/4827?view=long&pmid=12663789 |journal=J Virol |volume=77 |issue=8 |pages = 4827-35 |year=2003 |pmid = 12663789}}</ref> Once inside a human cell the virus hijacks the [[Host (biology)|host cell's]] own machinery, and begins to replicate. Poliovirus divides within gastrointestinal cells for about one week before penetrating the [[intestinal]] lining. Following penetration, the virus is absorbed into the [[blood]] via the [[mesentery]], and into the [[lymphatic system]] via the [[Peyer's patches]].

Once the virus enters the bloodstream it becomes a ''[[viremia]]'' and is 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  | date = 2006 | url = http://www.bact.wisc.edu/themicrobialworld/Polio.html  | accessdate = 2007-04-23}}</ref> In a small percentage of cases the virus spreads and replicates 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}}</ref> This sustained replication causes a secondary major viremia, and leads to the development of minor influenza-like symptoms.

Rarely, the major viremia progresses and the virus invades the central nervous system (CNS), causing a local [[inflammatory]] response. In most cases this causes a self limiting inflammation of the [[meninges]], the layers of tissue surrounding the [[brain]], causing non-paralytic ''[[aseptic meningitis]]''.<ref name=Chamberlin_2005 /> Penetration of the CNS provides no known benefit to the virus, and is quite possibly an "accidental" deviation of a normal gastrointestinal infection.<ref name= Mueller>{{cite journal |author=Mueller S, Wimmer E, Cello J |title=Poliovirus and poliomyelitis: a tale of guts, brains, and an accidental event |journal=Virus Res |volume=111 |issue=2 |pages=175-93 |year=2005 |pmid = 15885840}}</ref> The mechanisms by which poliovirus spreads to the CNS are poorly understood, but it appears to be primarily a chance event&mdash;largely independent of the age, gender, or socioeconomic position of the individual.<ref name=Mueller />

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

In approximately 1% of infections poliovirus spreads along certain nerve fiber pathways, preferentially replicating in and destroying [[motor neuron]]s within the [[spinal cord]], [[brain stem]], or [[motor cortex]], which leads to the development of paralytic poliomyelitis. The various forms of paralytic poliomyelitis (spinal, bulbar, and bulbospinal) vary only with the amount of neuronal damage and inflammation that occurs, and the region of the CNS that is affected. 

The destruction of neuronal cells produces [[lesion]]s within the [[Dorsal root ganglion|spinal ganglia]]; lesions can also be found in the [[reticular formation]], [[vestibular nuclei]], [[cerebellar vermis]], and deep [[cerebellar nuclei]].<ref name=Mueller />  Inflammation associated with 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 changes associated with paralytic disease occur in the [[hypothalamus]] and [[thalamus]].<ref name=Mueller /> The molecular mechanisms by which poliovirus causes paralytic disease are poorly understood. 

Early symptoms of paralytic polio include a high fever, headache, stiffness in the back and neck, asymmetrical weakness of various muscles, sensitivity to touch, difficulty swallowing, muscle pain, loss of superficial and deep [[reflex]]es, [[paresthesia]], irritability, constipation, or difficulty urinating. Paralysis generally develops 1 to 10 days after early symptoms begin, and progresses for 2 to 3 days. Paralysis is usually complete when the fever breaks.<ref name= Silverstein>{{cite book |author = 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 }}</ref> 

The likelihood of developing paralytic polio and the extent of paralysis increase with age. In children non-paralytic meningitis is the most likely consequence of CNS involvement, and paralysis occurs in only 1 in 1000 cases. In adults paralysis occurs in 1 in 75 cases.<ref name=Gawne_1995>{{cite journal | author = Gawne AC, Halstead LS | title = Post-polio syndrome: pathophysiology and clinical management | journal = Critical Review in Physical Medicine and Rehabilitation  | year = 1995 | volume = 7 | pages = 147–88 | url = http://www.ott.zynet.co.uk/polio/lincolnshire/library/gawne/ppspandcm-s00.html}}</ref> In children under 5 years of age paralysis of one leg is most common, while in adults extensive paralysis in the trunk and muscles of the [[chest]] and [[abdomen]] and affecting all four limbs—[[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=}}</ref> Paralysis rates also vary depending on the serotype of the infecting poliovirus. The highest rates of paralysis (1 in 200) are associated with poliovirus type 1, the lowest rates (1 in 2,000) are associated with type 2.<ref name=Nathanson>{{cite journal |author=Nathanson N, Martin J |title=The epidemiology of poliomyelitis: enigmas surrounding its appearance, epidemicity, and disappearance |journal=Am J Epidemiol |volume=110 |issue=6 |pages=672-92 |year=1979 |pmid=400274}}</ref> 

==== Spinal polio ====

[[Image:Polio spinal diagram.PNG|thumb|left|The location of [[motor neuron]]s in the [[Anterior horn (spinal cord)|anterior horn cells]] of the [[spinal column]].]] 

Spinal polio is the most common form of paralytic poliomyelitis. This form of the disease results from viral invasion of the [[motor neuron]]s of the [[Anterior horn (spinal cord)|anterior horn cells]], or the [[ventral]] (front) [[gray matter]] section in the [[spinal column]], which are responsible for movement of the [[muscle]]s, including the [[trunk]], [[limb]] and [[intercostal muscle]]s.<ref name= Henry1>{{cite book | author = Frauenthal HWA, Manning JVV | title = Manual of infantile paralysis, with modern methods of treatment. Pathology: p. 79-101 | publisher = Philadelphia Davis | year = 1914| url= http://books.google.com/books?vid=029ZCFMPZ0giNI1KiG6E&id=piyLQnuT-1YC&printsec=titlepage | oclc=  2078290}}</ref> 

Poliovirus invasion causes inflammation of the nerve cells, and results in damage or destruction of [[motor neuron]] [[ganglion|ganglia]]. When spinal neurons die ''[[Wallerian degeneration]]'' takes place, resulting in weakness of those muscles formerly [[innervate]]d by the now dead neurons.<ref name=Cono /> With the destruction of nerve cells, the muscles no longer receive signals from the brain or spinal cord; without nerve stimulation, the muscles begin to [[atrophy]], becoming weak, floppy and poorly controlled, and finally completely paralyzed.<ref name=Henry1 /> Progression to maximum paralysis is rapid (two to four days), and is usually associated with fever and muscle pain.<ref name= Cono>{{cite book | author = Cono J, Alexander LN | chapter = Chapter 10, Poliomyelitis. | title = Vaccine Preventable Disease Surveillance Manual | edition = 3rd ed. | pages = p. 10–1 | publisher = Centers for Disease Control and Prevention | year = 2002 | url = http://www.cdc.gov/nip/publications/surv-manual/chpt10_polio.pdf  | format = PDF}}</ref> Deep [[tendon]] [[reflexes]] are also affected and are usually absent or diminished; [[sensation]] (the ability to feel) however, is not affected in the paralyzed limbs.<ref name=Cono /> 

The extent of spinal paralysis depends on the part of the spinal cord affected, which may be [[cervical]], [[thoracic]], or [[lumbar]].<ref name=Guide>{{cite book |author= |title=Professional Guide to Diseases (Professional Guide Series) |publisher=Lippincott Williams & Wilkins |location=Hagerstwon, MD |year= 2005|pages=243-245 |isbn=1-58255-370-X |oclc= |doi=}}</ref> The virus may affect muscles on both sides of the body, but more often the paralysis is asymmetric and affects unbalanced parts of the body.<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 [[proximal]]ly (where the limb joins the body) than [[distal]]ly (i.e. the [[fingertip]]s and [[toe]]s).<ref name=Baron />

==== Bulbar polio ====

[[Image:Brain bulbar region.PNG|thumb|right|The location and anatomy of the bulbar region (in orange).]]

''Bulbar polio'' is a form of paralytic poliomyelitis which occurs when poliovirus invades and destroys nerves within the [[bulbar]] region of the [[brain stem]]. This form of the disease occurs in approximately 2% of cases of paralytic polio.<ref name = PinkBook />

The bulbar region is a [[white matter]] pathway which connects the [[cerebral cortex]] to the [[brainstem]]. In bulbar polio the destruction of these nerves weakens the muscles supplied by the [[cranial nerve]]s, producing symptoms of [[encephalitis]], and causing breathing, speaking and swallowing to become difficult.<ref name=Late /> Critical nerves affected are the [[glossopharyngeal nerve]], which in part controls swallowing and functions in the throat, tongue movement and taste; the [[vagus nerve]] that sends signals to the heart, intestines, and lungs and the [[accessory nerve]] that controls upper neck movement. Due to the effect on swallowing, secretions of [[mucus]] may build up in the airway causing suffocation.<ref name = Silverstein /> Other signs and symptoms of bulbar polio include: facial weakness caused by destruction of the [[trigeminal nerve]] and facial nerve which innervate cheeks, [[tear duct]]s, gums, and muscles of the face, among others; [[diplopia|double vision]], difficulty in chewing, and abnormal respiratory rate, depth, and rhythm, which may lead to [[respiratory arrest]]. [[Pulmonary edema]] and [[Shock (medical)|shock]] are also possible, and may be fatal.<ref name=Guide/><ref name=Mayo>{{cite web |author = Mayo Clinic Staff | date=2005-05-19 | url = http://www.mayoclinic.com/health/polio/DS00572/DSECTION=2 | title = Polio: Signs and symptoms | publisher = Mayo Foundation for Medical Education and Research (MFMER)| accessdate=2007-02-26}}</ref> 

Nineteen percent of all paralytic polio cases appear as a combination of the symptoms of both bulbar and spinal polio, this form of the disease is called  ''respiratory polio'' or ''bulbospinal polio''.<ref name= PinkBook /> In bulbospinal cases, the virus affects the upper part of the [[Cervical vertebrae|cervical spinal cord]] (C3-4-5), and paralysis of the [[Thoracic diaphragm|diaphragm]] occurs. The critical nerves affected are the [[phrenic nerve]] (the nerve driving the diaphragm to inflate the [[lungs]]) and the innervation of 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 [[respirator]]. It can lead to paralysis of the arms and legs and may also affect swallowing and heart functions.<ref name= Mayo/>

==Prognosis==

Patients with abortive polio infections recover completely. In those patients that develop 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 nerve cells affected by polio are completely destroyed, paralysis will be permanent; cells that are not destroyed but lose function temporarily may recover within 4–6 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/educa/August2004_HistoricalPerspective_Neumann.pdf  | format = PDF | journal=The Journal of orthopaedic and sports physical therapy |volume=34 |issue=8 |pages=479-92 |year=2004 |pmid=15373011}}</ref>  Fifty percent of patients with spinal polio recover fully, 25% recover with mild disability and 25% are left with a severe disability.<ref>{{cite book |author=Cuccurullo SJ |title=Physical Medicine and Rehabilitation Board Review |url= http://www.ncbi.nlm.nih.gov/books/bv.fcgi?&rid=physmedrehab.table.8357 | 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 [[viraemia]], and inversely proportional to the degree of [[immunity (medical)|immunity]].<ref name= Mueller>{{cite journal |author=Mueller S, Wimmer E, Cello J |title=Poliovirus and poliomyelitis: a tale of guts, brains, and an accidental event |journal=Virus Res |volume=111 |issue=2 |pages=175-93 |year=2005 |id=PMID 15885840}}</ref> Spinal polio is rarely fatal.<ref name=Silverstein />

[[Image:Polio sequelle.jpg|thumb|A child displaying a deformity of her right leg due to polio.]]

Without respiratory support, poliomyelitis with [[Respiration (physiology)|respiratory]] involvement is likely to result in [[suffocation]], or [[aspiration]] of secretions and resulting [[pneumonia]].<ref name= Goldberg>{{cite journal |author=Goldberg A |title=Noninvasive mechanical ventilation at home: building upon the tradition |url= http://www.chestjournal.org/cgi/content/full/121/2/321 |journal=Chest |volume=121 |issue=2 |pages=321-4 |year=2002 |id=PMID 11834636}}</ref> Overall 5–10% of patients with paralytic polio die due to the paralysis of muscles used for breathing. The mortality rate varies by age: 2%–5% of children, and up to 15%–30% of adults die.<ref name= PinkBook />  Without [[mechanical ventilation]], the bulbar form of paralytic poliomyelitis often results in death.<ref name= Mayo /> With respiratory support the mortality rate of bulbar polio ranges from 25% to 75%, depending on the age of the patient.<ref name=PinkBook />

===Recovery===

Many cases of poliomyelitis result in only temporary paralysis.<ref name=Henry1 /> Within a month, nerve impulses begin to return to the apparently paralyzed muscle; recovery is usually complete within six to eight months.<ref name=Neumann /> The [[neurophysiology|neurophysiological]] processes involved in recovery following acute paralytic poliomyelitis are quite effective; muscles are able to retain normal strength even after 50 percent of the original motor neurons have been lost.<ref>{{cite journal |author=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 : official journal of the International Federation of Clinical Neurophysiology |volume=110 |issue=11 |pages=1900-8 |year=1999 |pmid=10576485}}</ref> Paralysis remaining after one year is likely to be permanent, but 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 |author=Cashman NR, Covault J, Wollman RL, Sanes JR |title=Neural cell adhesion molecule in normal, denervated, and myopathic human muscle |journal=Ann. Neurol. |volume=21 |issue=5 |pages=481-9 |year=1987 |pmid=3296947}}</ref> These sprouts can [[reinnervate]] orphaned [[muscle fibers]] that have been denervated by acute polio infection,<ref name=Agre>{{cite journal |author=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}}</ref> restoring the capacity of muscle fibers to contract and improving strength.<ref>{{cite journal |author=Trojan DA, Cashman NR |title=Post-poliomyelitis syndrome |journal=Muscle Nerve |volume=31 |issue=1 |pages=6-19 |year=2005 |pmid=15599928}}</ref> Terminal sprouting may result in 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 ''[[Muscle hypertrophy|Myofiber hypertrophy]]''&mdash;enlargement of muscle fibers through exercise and activity&mdash;and transformation of [[Muscle fiber#Type II|type II muscle fibers]]  to [[Muscle fiber#Type I| type I muscle fibers]].<ref name = Grimby_1989>{{cite journal |author=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><ref name=Agre /> 

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

===Complications===

Residual complications of paralytic polio often result following the initial recovery process.<ref name= Late /> Muscle [[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 results when the muscles that pull the toes downward are working, but those that pull it upward are not, and foot naturally tends to drop toward the ground. If the problem is left untreated, the [[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 = 2007-07-31}}</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 [[scoliosis]]).<ref name= Aftereffects /> [[Osteoporosis]] and increased likelihood of [[bone fracture]]s may occur. Extended use of braces or wheelchairs may cause compression [[neuropathy]], as well as a loss of proper function of the [[veins]] in the legs, due to pooling of blood in paralyzed lower limbs.<ref name=MayoComps>{{cite web |author = Mayo Clinic Staff | date=2005-05-19 | url = http://www.mayoclinic.com/health/polio/DS00572/DSECTION=7  | title = Polio: Complications| publisher = Mayo Foundation for Medical Education and Research (MFMER)| accessdate=2007-02-26}}</ref>

Complications resulting from prolonged immobility involving the [[lungs]], [[kidney]]s and [[heart]] include [[pulmonary edema]], [[aspiration pneumonia]], [[urinary tract infection]]s, [[kidney stone]]s, [[paralytic ileus]], [[myocarditis]] and ''[[cor pulmonale]]''.<ref name=MayoComps />

=== Post-polio syndrome ===
{{main|Post-polio syndrome}}
Approximately one quarter of individuals who survive paralytic polio in childhood have developed additional symptoms decades after recovering from the acute poliovirus infection, notably muscle weakness, extreme fatigue, or paralysis. This condition is known as ''[[post-polio syndrome]]'' (PPS).<ref name=Cashman>{{cite journal |author=Trojan D, Cashman N |title=Post-poliomyelitis syndrome |journal=Muscle Nerve |volume=31 |issue=1 |pages=6-19 |year=2005 |pmid = 15599928}}</ref> The symptoms of PPS are thought to involve a failure of the over-sized motor units created during recovery from paralytic disease. PPS is observed in 28.5% of patients who had recovered from an acute polio infection.<ref name=Ramlow_1992>{{cite journal |author=Ramlow J, Alexander M, LaPorte R, Kaufmann C, Kuller L |title=Epidemiology of the post-polio syndrome |journal=Am. J. Epidemiol. |volume=136 |issue=7 |pages=769-86 |year=1992 |pmid=1442743}}</ref><ref name= Annals>{{cite journal |author=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=Ann Acad Med Singapore |volume=34 |issue=7 |pages=447-9 |year=2005 |pmid = 16123820}}</ref> Factors that increase the risk of PPS include the length of time since acute poliovirus infection, the presence of permanent residual impairment after recovery from the acute illness, and overuse and disuse of neurons.<ref name=Cashman /> Post-polio syndrome is not an infectious process, and persons experiencing the syndrome do not shed poliovirus.<ref name=PinkBook />

== Diagnosis ==

A laboratory diagnosis of poliomyelitis is usually made based on recovery of poliovirus from the stool or [[pharynx]]. Neutralizing [[antibodies]] to poliovirus can be diagnostic and are generally detected in the blood of infected patients early in the course of infection.<ref name=PinkBook /> Analysis of the patient's [[cerebrospinal fluid]] (CSF), which is collected by a [[lumbar puncture]] ("spinal tap") reveals an increased number of [[white blood cell]]s (primarily [[lymphocyte]]s) and a mildly elevated protein level.<ref name=MayoScreen>{{cite web |author = Mayo Clinic Staff | date=2005-05-19 | url = http://www.mayoclinic.com/health/polio/DS00572/DSECTION=6 | title = Polio: Screening and diagnosis | publisher = Mayo Foundation for Medical Education and Research (MFMER)| accessdate=2007-02-26}}</ref> Detection of virus from the CSF is diagnostic of paralytic polio, but rarely occurs.

If poliovirus is isolated from a patient experiencing acute flaccid paralysis it is further tested, using [[oligonucleotide]] mapping ([[genetic fingerprint]]ing), or more recently by [[PCR]] amplification, to determine if the virus is “wild type” (that is, the virus encountered in nature) or vaccine type (is 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 |url= http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=8784577| journal=J Clin Microbiol |volume=34 |issue=7 |pages=1722-5 |year=1996 |pmid=8784577}}</ref>  For each reported case of paralytic polio caused by wild poliovirus, it is estimated that another 200 to 3,000 contagious [[asymptomatic carrier]]s exist.<ref>{{cite journal |authorlink = Atul Gawande |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 = 2004-01-12 | accessdate = 2007-05-13}}</ref> Therefore, isolation of wild poliovirus constitutes a [[public health]] emergency, and appropriate efforts to control the spread of the disease must be initiated immediately.<ref name= Cono/>

== Treatment ==
[[Image:Womanonsideinlung.jpg|thumb|left|A modern negative pressure ventilator (iron lung).]]

No cure for polio exists, and the focus of modern polio treatment has been on increasing comfort, 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=MayoTreat>{{cite web |author = Mayo Clinic Staff | date=2005-05-19 | url =http://www.mayoclinic.com/health/polio/DS00572/DSECTION=8  | title = Polio: Treatment| publisher = Mayo Foundation for Medical Education and Research (MFMER)| accessdate=2007-02-26}}</ref> Treatment of polio also often requires long-term rehabilitation including [[physical therapy]], braces, corrective shoes and, in some cases, [[orthopedic surgery]].<ref name=Guide />

Portable [[ventilator]]s may be required to support breathing. Historically, a noninvasive negative-pressure ventilator (more commonly called an ''[[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 that are worn over the [[chest]] and [[abdomen]].<ref name= Goldberg />

Other [[History of poliomyelitis#Historical treatments|historical treatments for polio]] have included [[hydrotherapy]], [[electrotherapy]] and surgical treatments such as tendon lengthening and nerve grafting.<ref name=Henry1 /> The use of devices such as rigid [[brace]]s and body casts&mdash;which tended to cause [[muscle atrophy]] due to the limited movement of the user&mdash;were also touted as effective treatments.<ref name = Oppewal>{{cite journal |author=Oppewal S |title=Sister Elizabeth Kenny, an Australian nurse, and treatment of poliomyelitis victims |journal=Image J Nurs Sch |volume=29 |issue=1 |pages=83-7 |year=1997 |pmid=9127546}}</ref> Massage, passive motion exercises, and [[vitamin C]] were also used to treat polio victims, with varying degrees of success.<ref name= Henry1/><ref>{{cite journal | author = Klenner FR | title=The Treatment of Poliomyelitis and Other Virus Diseases with Vitamin C | url= http://www.orthomed.com/polio.htm | journal=Southern Medicine & Surgery | volume=111 | issue=7 | year = 1949 }}</ref>

==Prevention==
=== Antibody serum ===

In 1950 [[William Hammon]] at the University of Pittsburgh isolated a [[serum]] from the [[blood]] of polio survivors.<ref name=Hammon_1955>{{cite journal |author=Hammon W |title=Passive immunization against poliomyelitis |journal=Monogr Ser World Health Organ |volume=26 |issue= |pages=357-70 |year = 1955 |pmid=14374581}}</ref>  Hammon proposed that the serum, 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 [[clinical trial]] were promising; the serum was shown to be about 80% effective in preventing the development of paralytic poliomyelitis.<ref>{{cite journal |author=Hammon W, Coriell L, Ludwig E, ''et al'' |title=Evaluation of Red Cross gamma globulin as a prophylactic agent for poliomyelitis. 5. Reanalysis of results based on laboratory-confirmed cases |journal=J Am Med Assoc |volume=156 |issue=1 |pages=21-7 |year=1954 |pmid=13183798}}</ref> The serum was also shown to reduce the severity of the disease in patients that developed polio.<ref name=Hammon_1955 /> The antibody approach was later deemed impractical for widespread use, however, due in large part to the limited supply of blood plasma, and the medical community turned its focus to 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=Am J Public Health |volume=95 |issue=5 |pages=790-9 |year=2005 |pmid=15855454}}</ref>
[[Image:Poliodrops.jpg|thumb|right|A child receives oral polio vaccine.]]

=== Vaccine ===
{{main|Polio vaccine}}

Two polio vaccines are used throughout the world to combat [[polio]]. Both vaccines 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 ''[[herd immunity]]'').<ref name=Fine>{{cite journal |author=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=Am J Epidemiol |volume=150 |issue=10 |pages=1001-21 |year=1999 |pmid=10568615}}</ref> 

The first polio vaccine was developed in 1952 by [[Jonas Salk]] at the University of Pittsburgh, and announced to the world on April 12, 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 |format= |work=The Salk vaccine: 50 years later- second of two parts |publisher= Pittsburgh Post-Gazette|date= April 04, 2005 |accessdate= 2007-04-30 }}</ref> The Salk vaccine, or ''inactivated poliovirus vaccine'' (IPV), is based on poliovirus grown in a type of monkey [[kidney]] tissue culture ([[Vero cell]] line), which is chemically-inactivated with [[formalin]].<ref name=Kew_2005 /> After two doses of IPV, ninety percent or more of individuals develop protective antibody to all three [[serotype]]s of poliovirus, and at least 99% are immune to poliovirus following three doses.<ref name = PinkBook /> IPV is currently the vaccine of choice in most countries.

Eight years after Salk's success, [[Albert Sabin]] developed an ''oral polio vaccine'' (OPV) using live but weakened ([[attenuated]]) virus, produced by the repeated passage of the virus through non-human cells at sub-[[physiological]] temperatures.<ref name=Sabin_1973>{{cite journal | author = Sabin AB, Boulger LR | title = History of Sabin attenuated poliovirus oral live vaccine strains | journal = J Biol Stand | year = 1973 | volume = 1 | pages = 115–8 }}</ref> [[Clinical trial|Human trials]] of Sabin's vaccine began in 1957 and it was licensed in 1962.<ref>{{cite web | title = A Science Odyssey: People and Discoveries | publisher = PBS | year = 1998 | url = http://www.pbs.org/wgbh/aso/databank/entries/dm52sa.html | accessdate = 2007-08-14}}</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 [[nervous system]] tissue.<ref>{{cite journal |author=Sabin A, Ramos-Alvarez M, Alvarez-Amezquita J, ''et al'' |title=Live, orally given poliovirus vaccine. Effects of rapid mass immunization on population under conditions of massive enteric infection with other viruses |journal=JAMA |volume=173 |issue= |pages=1521-6 |year=1960 |pmid =14440553}}</ref> OPV produces excellent immunity in the [[intestine]], which helps prevent infection with wild virus in areas where the virus is [[Endemic (epidemiology)|endemic]].<ref name=Peds>{{cite journal |author= |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}}</ref> A single dose of oral polio vaccince produces immunity to all three poliovirus serotypes in approximately 50% of recipients. Three doses of live-attenuated OPV produce protective antibody to all three poliovirus types in more than 95% of recipients.<ref name=PinkBook />

== Eradication ==
{{main|Poliomyelitis eradication}}

Following the widespread use of poliovirus vaccine in the mid-1950s, the incidence of poliomyelitis declined rapidly in many industrialized countries. A global effort to eradicate polio began in 1988 and was led by the [[World Health Organization]], UNICEF, and The Rotary Foundation.<ref name= Watch>{{cite web| last =  Mastny| first = Lisa | title = Eradicating Polio: A Model for International Cooperation |publisher =  Worldwatch Institute | date = January 25, 1999 | url = http://www.worldwatch.org/node/1644 | accessdate =  2007-02-02}}</ref> These efforts have reduced 99% of annual diagnosed cases from an estimated 350,000 cases in 1988 to fewer than 2,000 cases in 2006.<ref name=eradication>{{cite journal |author= |title=Update on vaccine-derived polioviruses |journal=MMWR Morb Mortal Wkly Rep |volume=55 |issue=40 |pages=1093-7 |year=2006 |pmid=17035927}}</ref> Should eradication be successful it will represent only the second time mankind has ever completely eliminated a disease. The first such disease was [[smallpox]], which was officially eradicated in 1979.<ref name=WHO_smallpox>{{cite web | title=Smallpox | work=WHO Factsheet | url=http://www.who.int/mediacentre/factsheets/smallpox/en/ | accessdate = 2006-09-23}}</ref> 

A number of eradication milestones have already been reached, and several regions of the world have been certified polio-free. The Americas were declared polio-free in 1994.<ref name=MMWR_1994>{{cite journal| author= | title = International Notes Certification of Poliomyelitis Eradication -- the Americas, 1994 | journal =  Morbidity and Mortality Weekly Report |  publisher = Centers for Disease Control and Prevention | volume= 43 | issue= 39 | pages = 720-722 | year=1994 | url = http://www.cdc.gov/mmwr/preview/mmwrhtml/00032760.htm | pmid = 7522302 }}</ref> In 2000  polio was officially eradicated in 36 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 Educ Res | year = 2001 | volume = 16 | issue = 1 | pages = p. 109 | url= http://her.oxfordjournals.org/cgi/reprint/16/1/109.pdf  | format = PDF}}</ref><ref name="D'Souza_2002">{{cite journal |author=D'Souza R, Kennett M, Watson C |title=Australia declared polio free |journal=Commun Dis Intell |volume=26 |issue=2 |pages=253-60 |year=2002 |pmid=12206379}}</ref> Europe was declared polio-free in 2002.<ref name=WHO_Europe_2002>{{cite news | title = Europe achieves historic milestone as Region is declared polio-free | work = Press release | pages =  |  publisher = European Region of the World Health Organization | date = 2002-06-21 | url = http://www.euro.who.int/mediacentre/PR/2002/20020620_1 | accessdate = 2007-02-02 }}</ref> Today, polio remains endemic in just four countries: Nigeria, India, Pakistan, and Afghanistan.<ref name=eradication/>

== History ==
{{main|History of poliomyelitis}}
[[Image:Polio Egyptian Stele.jpg|thumb|right|An Egyptian stele thought to represent a polio victim. 18th Dynasty (1403 - 1365 BC).]]
The effects of a polio infection have been known since prehistory: Ancient Egypt paintings and carvings depict otherwise healthy people with withered limbs, and children walking with canes at a young age.<ref name= Sass>{{cite book |author = Sass Ej, Gottfried G, Sorem, A (eds.) | title = Polio's legacy: an oral history | publisher = University Press of America |location=Washington, D.C |year=1996 |isbn=0-7618-0144-8 |url=http://www.cloudnet.com/~edrbsass/poliotimeline.htm}}</ref> The first clinical description of poliomyelitis was provided by the British physician Michael Underwood in 1789&mdash;he refers to polio as “a debility of the lower extremities".<ref name=Underwood_1789>{{cite book | last = Underwood | first = Michael | title = Debility of the lower extremities. ''In:'' A treatise on the dieases <nowiki>[sic]</nowiki> of children, with general directions for the management of infants from the birth (1789) | volume = 2 | publisher = Philadelphia: Printed by T. Dobson, no. 41, South Second-Street | year = 1793 | pages = pp. 254&ndash;6 | series = Early American Imprints, 1st series, no. 26291 (filmed); Copyright 2002 by the American Antiquarian Society | url=http://catalog.mwa.org/cgi-bin/Pwebrecon.cgi?v1=1&ti=1,1&Search%5FArg=Underwood%2C%20Michael&Search%5FCode=OPAU&CNT=10&PID=23682&SEQ=20070223225426&SID=1 | format = fee required | accessdate = 2007-02-23 }}</ref> The work of physicians [[Jakob Heine]] in 1840 and Karl Oskar Medin in 1890 led to the disease being known as ''Heine-Medin disease''.<ref name=Pearce_2005>{{cite journal |author=Pearce J |title=Poliomyelitis (Heine-Medin disease) |journal=J Neurol Neurosurg Psychiatry |volume=76 |issue=1 |pages=128 |year=2005 |url=http://jnnp.bmj.com/cgi/content/full/76/1/128 | format = fee required | pmid=15608013}}</ref><ref name= Sass/> The disease was later called ''infantile paralysis'', based on its propensity to affect children. 

Prior to the 20th century, polio infections were rarely seen in infants before 6 months of age and most cases occurred in children 6 months to 4 years of age.<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://www.who.int/vaccines-documents/DocsPDF-IBI-e/mod6_e.pdf | format = PDF | date = 1993 | accessdate = 2007-05-08}}</ref> Poorer [[sanitation]] of the time resulted in a constant exposure to the virus, which enhanced a natural [[immunity (medical)|immunity]] within the population. In developed countries during the late 19th and early 20th centuries, improvements were made in community sanitation, including improved sewage disposal and clean water supplies. These changes also drastically increased the proportion of children and adults at risk of paralytic polio infection, by reducing childhood exposure and immunity to the disease. 

Around 1900, small, localized paralytic polio [[epidemic]]s began to appear in Europe and the United States.<ref name = Trevelyan>{{cite journal |author=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| url= http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=16741562 |journal=Ann Assoc Am Geogr |volume=95 |issue=2 |pages=269-293 |year=2005 |pmid=16741562}}</ref> Outbreaks reached [[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 ed. | publisher = McGraw-Hill | year =1990  | pages = p. 558-576 | isbn = 007068328X }}</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 would be 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= http://www.fda.gov/bbs/topics/CONSUMER/CON00006.html |journal= FDA Consumer |volume = 25 |issue = 5 |pages = 21-5 |year=1991}}</ref>

The polio epidemics changed not only the lives of those who survived them, but also affected profound cultural changes: the emergence of grassroots fund-raising campaigns that would revolutionize medical philanthropy, the rise of [[Physical therapy|rehabilitation therapy]] and—through campaigns for the social and civil rights of the [[disabled]]—polio survivors helped to spur the modern [[disability rights movement]]. Today polio survivors are one of the largest disabled groups in the world. 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.com/aboutus/791_1718.asp | date = 2001-06-01 | accessdate = 2007-08-07}}</ref> In 1977 there were 254,000 persons living in the United States who had been paralyzed by polio.<ref>{{cite journal | author = 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 | doi = | accessdate = 2007-06-04}}</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/>

== See also ==

*[[Polio Hall of Fame]]

== Notes and references ==

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== Further reading ==
<div class="references-small" style="-moz-column-count:2; column-count:2;">
*{{cite book | author = Frauenthal HWA, Manning JVV | title = Manual of infantile paralysis, with modern methods of treatment: Pathology. | publisher = Davis | location = Philadelphia| year = 1914| url= http://books.google.com/books?vid=029ZCFMPZ0giNI1KiG6E&id=piyLQnuT-1YC&printsec=titlepage | pages = pp. 79-101 | oclc = 2078290}} (Full text available from Google Books, with hundreds of pictures.)

* {{cite book |author = Huckstep RL |title=Poliomyelitis: a guide for developing countries - including appliances and rehabilitation for the disabled |url= http://www.worldortho.com/index.php?option=com_content&task=view&id=522&Itemid=267 |publisher=Churchill Livingstone |location=Edinburgh |year=1975 |pages= |isbn=0443013128 |oclc= |doi=}} (A look at the modern polio patient and polio treatment techniques.)
</div>

== External links ==
{{commonscat|Polio}}

;General:
* [http://americanhistory.si.edu/polio/index.htm What ever happened to Polio?] An exhibit from the Smithsonian National Museum of American History.
* [http://www.healthheritageresearch.com/MCPlague.html The Middle-Class Plague: Epidemic Polio and the Canadian State.]
* [http://archives.cbc.ca/IDD-1-75-363/science_technology/polio/ CBC Digital Archives - Polio: Combating the Crippler] Video and Radio reports related to Polio.
* [http://rnzcgp.org.nz/news/nzfp/June1999/orrc.htm Poliovirus in New Zealand 1915-1997]
* [http://www.scq.ubc.ca/?p=45 Polio: A Virus' Struggle] - an amusing yet educational graphic novella from the Science Creative Quarterly (in [[pdf]] format).

'''People and polio'''

* [http://www.paho.org/English/DPI/Number2_article8.htm Fermín: Making Polio History] An article about Luis Fermín Tenorio Cortez, the last case of polio reported in the Americas.
* [http://www.johnprestwich.btinternet.co.uk/40-years-a-layabout.htm A UK Polio survivor] - An account of John Prestwich who lived 50 years in an iron lung.
* [http://www.post-polio.org/ Post-Polio Health International]

<br>
{{Viral diseases}}
{{SIB}}

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[[uk:Поліомієліт]]
[[zh:小兒麻痺]]



[[Category:Poliomyelitis|*]]
[[Category:Infectious disease]]

[[pl:Choroba Heinego-Medina]]
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