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Wikipedia

Polio

Poliomyelitis, commonly shortened to polio, is an infectious disease caused by the poliovirus.[1] Approximately 70% of cases are asymptomatic; mild symptoms which can occur include sore throat and fever; in a proportion of cases more severe symptoms develop such as headache, neck stiffness, and paresthesia.[1][3] These symptoms usually pass within one or two weeks.[1] A less common symptom is permanent paralysis, and possible death in extreme cases.[1] Years after recovery, post-polio syndrome may occur, with a slow development of muscle weakness similar to that which the person had during the initial infection.[2]

Polio
Other namesPoliomyelitis, infantile paralysis, Heine-Medin disease
A man with a wasted right leg due to poliomyelitis
Pronunciation
SpecialtyNeurology, Infectious disease
SymptomsFever, sore throat[1]
ComplicationsMuscle weakness resulting in paralysis;[1] Post-polio syndrome[2]
TypesWild PV types 1,2 & 3; vaccine-derived PV[1]
CausesPoliovirus spread by fecal–oral route[1]
Risk factorsPoor hygiene
Diagnostic methodFinding the virus in the feces or antibodies in the blood[1]
PreventionPolio vaccine[3]
TreatmentNo treatment other than supportive care[3]
Frequency6 (wild) + 691 (vaccine-derived) in 2021[4]

Polio occurs naturally only in humans.[1] It is highly infectious, and is spread from person to person either through fecal-oral transmission[1][5] (e.g. poor hygiene, or by ingestion of food or water contaminated by human feces), or via the oral-oral route.[1] Those who are infected may spread the disease for up to six weeks even if no symptoms are present.[1] The disease may be diagnosed by finding the virus in the feces or detecting antibodies against it in the blood.[1]

Poliomyelitis has existed for thousands of years, with depictions of the disease in ancient art.[1] The disease was first recognized as a distinct condition by the English physician Michael Underwood in 1789,[1][6] and the virus that causes it was first identified in 1909 by the Austrian immunologist Karl Landsteiner.[7][8] Major outbreaks started to occur in the late 19th century in Europe and the United States,[1] and in the 20th century, it became one of the most worrying childhood diseases.[9] Following the introduction of polio vaccines in the 1950s polio incidence declined rapidly.[1]

Once infected, there is no specific treatment.[3] The disease can be prevented by the polio vaccine, with multiple doses required for lifelong protection.[3] There are two broad types of polio vaccine; an injected vaccine using inactivated poliovirus and an oral vaccine containing attenuated (weakened) live virus.[1] Through the use of both types of vaccine, incidence of wild polio has decreased from an estimated 350,000 cases in 1988[3] to 6 confirmed cases in 2021, confined to just three countries.[10] There are rare incidents of disease transmission and/or of paralytic polio associated with the attenuated oral vaccine and for this reason the injected vaccine is preferred.[11]

Signs and symptoms

Outcomes of poliovirus infection in children
Outcome Proportion of cases[1]
No symptoms 72%
Minor illness 24%
Nonparalytic aseptic
meningitis
1–5%
Paralytic poliomyelitis 0.1–0.5%
— Spinal polio 79% of paralytic cases
— Bulbospinal polio 19% of paralytic cases
— Bulbar polio 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 central nervous system (CNS), sometimes called abortive poliomyelitis, and a major illness involving the CNS, which may be paralytic or nonparalytic.[12] Adults are more likely to develop symptoms, including severe symptoms, than children.[1]

In most people with a normal immune system, a poliovirus infection is asymptomatic. In about 25% of cases, the infection produces minor symptoms which may include sore throat and low fever.[3] These symptoms are temporary and full recovery occurs within one or two weeks.[1][3]

In about 1 percent of infections the virus can migrate from the gastrointestinal tract into the central nervous system (CNS).[1] Most patients with CNS involvement develop nonparalytic aseptic meningitis, with symptoms of headache, neck, back, abdominal and extremity pain, fever, vomiting, stomach pain, lethargy, and irritability.[13][14][15] 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.[16] The weakness most often involves the legs, but may less commonly involve the muscles of the head, neck, and diaphragm.[1] Depending on the site of paralysis, paralytic poliomyelitis is classified as spinal, bulbar, or bulbospinal. In those who develop paralysis, between 2 and 10 percent die as the paralysis affects the breathing muscles.[3]

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, seizures and spastic paralysis.[17]

Cause

 
A TEM micrograph of poliovirus

Poliomyelitis is caused by infection with a member of the genus Enterovirus known as poliovirus (PV). This group of RNA viruses colonize the gastrointestinal tract[18] – specifically the oropharynx and the intestine. The incubation time (form the first signs and symptoms) ranges from three to 35 days, with a more common span of six to 20 days.[1] PV does not affect any species other than humans.[19] Its structure is quite simple, composed of a single (+) sense RNA genome enclosed in a protein shell called a capsid.[19] In addition to protecting the virus' genetic material, the capsid proteins enable poliovirus to infect certain types of cells. Three serotypes of poliovirus have been identified – wild poliovirus type 1 (WPV1), type 2 (WPV2), and type 3 (WPV3) – each with a slightly different capsid protein.[20] All three are extremely virulent and produce the same disease symptoms.[19] PV1 is the most commonly encountered form, and the one most closely associated with paralysis.[21] WPV2 was certified as eradicated in 2015 and WPV3 certified as eradicated in 2019.[22]

Individuals who are exposed to the virus, either through infection or by immunization via polio vaccine, develop immunity. In immune individuals, IgA antibodies against poliovirus are present in the tonsils and gastrointestinal tract and able to block virus replication; IgG and IgM antibodies against PV can prevent the spread of the virus to motor neurons of the central nervous system.[23] Infection or vaccination with one serotype of poliovirus does not provide immunity against the other serotypes, and full immunity requires exposure to each serotype.[23]

A rare condition with a similar presentation, nonpoliovirus poliomyelitis, may result from infections with enteroviruses other than poliovirus.[24]

The oral polio vaccine contains weakened viruses that can replicate. On rare occasions, these may be transmitted from the vaccinated person to other people, who may display symptoms of polio. In communities with good vaccine coverage transmission is limited, and the virus dies out. In communities with low vaccine coverage, this weakened virus may continue to circulate.[25] Polio arising from this cause is referred to as circulating vaccine-derived polio (cVDPV) in order to distinguish it from the natural or "wild" poliovirus (WPV).[26]

Transmission

Poliomyelitis is highly contagious via the fecal–oral (intestinal source) and the oral–oral (oropharyngeal source) routes.[23] In endemic areas, wild polioviruses can infect virtually the entire human population.[27] It is seasonal in temperate climates, with peak transmission occurring in summer and autumn.[23] These seasonal differences are far less pronounced in tropical areas.[27] The time between first exposure and first symptoms, known as the incubation period, is usually 6 to 20 days, with a maximum range of 3 to 35 days.[28] Virus particles are excreted in the feces for several weeks following initial infection.[28] The disease is transmitted primarily via the fecal–oral route, by ingesting contaminated food or water. It is occasionally transmitted via the oral–oral route,[21] a mode especially visible in areas with good sanitation and hygiene.[23] 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.[21]

Factors that increase the risk of polio infection or affect the severity of the disease include immune deficiency,[29] malnutrition,[30] physical activity immediately following the onset of paralysis,[31] skeletal muscle injury due to injection of vaccines or therapeutic agents,[32] and pregnancy.[33] Although the virus can cross the maternal-fetal barrier during pregnancy, the fetus does not appear to be affected by either maternal infection or polio vaccination.[34] Maternal antibodies also cross the placenta, providing passive immunity that protects the infant from polio infection during the first few months of life.[35]

Pathophysiology

 
A photomicrograph of the lumbar spinal cord depicting an infarct due to Polio Type III surrounding the anterior spinal artery

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 CD155, on the cell membrane.[36] The virus then hijacks the host cell's own machinery, and begins to 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 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.[37]

Known as 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.[38] In a small percentage of cases, it can spread and replicate in other sites, such as brown fat, the reticuloendothelial tissues, and muscle.[39] 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 meninges, the layers of tissue surrounding the brain, which is known as nonparalytic aseptic meningitis.[13] Penetration of the CNS provides no known benefit to the virus, and is quite possibly an incidental deviation of a normal gastrointestinal infection.[40] 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.[40]

Paralytic polio

 
Denervation of skeletal muscle tissue secondary to poliovirus infection can lead to paralysis.

In around one percent of infections, poliovirus spreads along certain nerve fiber pathways, preferentially replicating in and destroying motor neurons within the spinal cord, brain stem, or 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 lesions within the spinal ganglia; these may also occur in the reticular formation, vestibular nuclei, cerebellar vermis, and deep cerebellar nuclei.[40] 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.[13] Other destructive changes associated with paralytic disease occur in the forebrain region, specifically the hypothalamus and thalamus.[40] 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, muscle pain, loss of superficial and deep reflexes, 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.[41]

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.[42] In children under five years of age, paralysis of one leg is most common; in adults, extensive paralysis of the chest and abdomen also affecting all four limbs – quadriplegia – is more likely.[43] 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.[44]

Spinal polio

 
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) 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.[16] Virus invasion causes inflammation of the nerve cells, leading to damage or destruction of motor neuron ganglia. When spinal neurons die, Wallerian degeneration takes place, leading to weakness of those muscles formerly innervated by the now-dead neurons.[45] With the destruction of nerve cells, the muscles no longer receive signals from the brain or spinal cord; without nerve stimulation, the muscles atrophy, becoming weak, floppy and poorly controlled, and finally completely paralyzed.[16] Maximum paralysis progresses rapidly (two to four days), and usually involves fever and muscle pain. Deep tendon reflexes are also affected, and are typically absent or diminished; sensation (the ability to feel) in the paralyzed limbs, however, is not affected.[46]

The extent of spinal paralysis depends on the region of the cord affected, which may be cervical, thoracic, or lumbar.[47] The virus may affect muscles on both sides of the body, but more often the paralysis is asymmetrical.[37] Any limb or combination of limbs may be affected – one leg, one arm, or both legs and both arms. Paralysis is often more severe proximally (where the limb joins the body) than distally (the fingertips and toes).[37]

Bulbar polio

 
The location and anatomy of the bulbar region (in orange)

Making up about two percent of cases of paralytic polio, bulbar polio occurs when poliovirus invades and destroys nerves within the bulbar region of the brain stem.[1] The bulbar region is a white matter pathway that connects the cerebral cortex to the brain stem. The destruction of these nerves weakens the muscles supplied by the cranial nerves, producing symptoms of encephalitis, and causes difficulty breathing, speaking and swallowing.[15] Critical nerves affected are the glossopharyngeal nerve (which partially controls swallowing and functions in the throat, tongue movement, and taste), the vagus nerve (which sends signals to the heart, intestines, and lungs), and the accessory nerve (which controls upper neck movement). Due to the effect on swallowing, secretions of mucus may build up in the airway, causing suffocation.[41] Other signs and symptoms include facial weakness (caused by destruction of the trigeminal nerve and facial nerve, which innervate the cheeks, tear ducts, gums, and muscles of the face, among other structures), double vision, difficulty in chewing, and abnormal respiratory rate, depth, and rhythm (which may lead to respiratory arrest). Pulmonary edema and shock are also possible and may be fatal.[47]

Bulbospinal polio

Approximately 19 percent of all paralytic polio cases have both bulbar and spinal symptoms; this subtype is called respiratory or bulbospinal polio.[1] 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 ventilator. It can lead to paralysis of the arms and legs and may also affect swallowing and heart functions.[48]

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.[49]

A laboratory diagnosis is usually made based on the recovery of poliovirus from a stool sample or a swab of the pharynx. Antibodies to poliovirus can be diagnostic, and are generally detected in the blood of infected patients early in the course of infection.[1] Analysis of the patient's cerebrospinal fluid (CSF), which is collected by a lumbar puncture ("spinal tap"), reveals an increased number of white blood cells (primarily lymphocytes) and a mildly elevated protein level. Detection of virus in the CSF is diagnostic of paralytic polio but rarely occurs.[1]

If poliovirus is isolated from a patient experiencing acute flaccid paralysis, it is further tested through oligonucleotide mapping (genetic fingerprinting), or more recently by PCR amplification, to determine whether it is "wild type" (that is, the virus encountered in nature) or "vaccine type" (derived from a strain of poliovirus used to produce polio vaccine).[50] 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 asymptomatic carriers exist.[51]

Prevention

Passive immunization

In 1950, William Hammon at the University of Pittsburgh purified the gamma globulin component of the blood plasma of polio survivors.[52] 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 clinical trial were promising; the gamma globulin was shown to be about 80 percent effective in preventing the development of paralytic poliomyelitis.[53] It was also shown to reduce the severity of the disease in patients who developed polio.[52] 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.[54]

Vaccine

 
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 and are effective in protecting individuals from disease.

The first candidate polio vaccine, based on one serotype of a live but 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.[55] 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.[56]

The second polio virus vaccine was developed in 1952 by Jonas Salk at the University of Pittsburgh, and announced to the world on 12 April 1955.[57][58] 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.[23] After two doses of inactivated poliovirus vaccine (given by injection), 90 percent or more of individuals develop protective antibody to all three serotypes of poliovirus, and at least 99 percent are immune to poliovirus following three doses.[1]

Subsequently, Albert Sabin developed another live, oral polio vaccine (OPV). It was produced by the repeated passage of the virus through nonhuman cells at subphysiological temperatures.[59] 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.[60] 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.[1] Human trials of Sabin's vaccine began in 1957,[61] and in 1958 it was selected, in competition with the live vaccines of Koprowski and other researchers, by the US National Institutes of Health.[56] Licensed in 1962,[61] it rapidly became the only polio vaccine used worldwide.[56]

OPV efficiently blocks person-to-person transmission of wild poliovirus by oral-oral and fecal-oral routes, thereby protecting both individual vaccine recipients and the wider community (herd immunity).[62] IPV confers good immunity but is less effective at preventing spread of wild poliovirus by the fecal-oral route.[63]

 
Wild polio vs cVDVP cases (2000–2019)

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 endemic), it has been the vaccine of choice for controlling poliomyelitis in many countries.[64] 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.[28] 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.[65] Most 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.[66]

Treatment

There is no cure for polio, but there are treatments. 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.[67] Treatment of polio often requires long-term rehabilitation, including occupational therapy, physical therapy, braces, corrective shoes and, in some cases, orthopedic surgery.[47]

Portable ventilators 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 worn over the chest and abdomen.[68]

Other historical treatments for polio include hydrotherapy, electrotherapy, massage and passive motion exercises, and surgical treatments, such as tendon lengthening and nerve grafting.[16]

Sister Elizabeth Kenny's Kenny regimen is now the hallmark for the treatment of paralytic polio.[69]

Prognosis

 
A girl with genu recurvatum 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.[70] 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.[70] Half the patients with spinal polio recover fully; one-quarter recover with mild disability, and the remaining quarter are left with severe disability.[71] The degree of both acute paralysis and residual paralysis is likely to be proportional to the degree of viremia, and inversely proportional to the degree of immunity.[40] Spinal polio is rarely fatal.[41]

Without respiratory support, consequences of poliomyelitis with respiratory involvement include suffocation or pneumonia from aspiration of secretions.[68] Overall, 5 to 10 percent of patients with paralytic polio die due to the paralysis of muscles used for breathing. The case fatality rate (CFR) varies by age: 2 to 5 percent of children and up to 15 to 30 percent of adults die.[1] Bulbar polio often causes death if respiratory support is not provided;[48] with support, its CFR ranges from 25 to 75 percent, depending on the age of the patient.[1][72] When intermittent positive pressure ventilation is available, the fatalities can be reduced to 15 percent.[73]

Recovery

Many cases of poliomyelitis result in only temporary paralysis.[16] Generally in these cases, nerve impulses return to the paralyzed muscle within a month, and recovery is complete in six to eight months.[70] The 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.[74] Paralysis remaining after one year is likely to be permanent, although some recovery of muscle strength is possible up to 18 months after infection.[70]

One mechanism involved in recovery is nerve terminal sprouting, in which remaining brainstem and spinal cord motor neurons develop new branches, or axonal sprouts.[75] These sprouts can reinnervate orphaned muscle fibers that have been denervated by acute polio infection,[76] restoring the fibers' capacity to contract and improving strength.[77] Terminal sprouting may generate a few significantly enlarged motor neurons doing work previously performed by as many as four or five units:[42] 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 myofiber hypertrophy – enlargement of muscle fibers through exercise and activity – and transformation of type II muscle fibers to type I muscle fibers.[76][78]

In addition to these physiological processes, the body can compensate for residual paralysis in other ways. Weaker muscles can be used at a higher than usual intensity relative to the muscle's maximal capacity, little-used muscles can be developed, and ligaments can enable stability and mobility.[78]

Complications

Residual complications of paralytic polio often occur following the initial recovery process.[15] 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 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 Achilles tendons at the back of the foot retract and the foot cannot take on a normal position. People with polio that develop equinus foot cannot walk properly because they cannot put their heels on the ground. A similar situation can develop if the arms become paralyzed.[79]

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).[79] Osteoporosis and increased likelihood of bone fractures may occur. An intervention to prevent or lessen length disparity can be to perform an epiphysiodesis on the distal femoral and proximal tibial/fibular condyles, so that limb's growth is artificially stunted, and by the time of 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 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.[48][80] Complications from prolonged immobility involving the lungs, kidneys and heart include pulmonary edema, aspiration pneumonia, urinary tract infections, kidney stones, paralytic ileus, myocarditis and cor pulmonale.[48][80]

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,[81] notably new muscle weakness and extreme fatigue. This condition is known as post-polio syndrome (PPS) or post-polio sequelae.[77] The symptoms of PPS are thought to involve a failure of the oversized motor units created during the recovery phase of the paralytic disease.[82][83] 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.[77] Post-polio syndrome is not an infectious process, and persons experiencing the syndrome do not shed poliovirus.[1]

Orthotics

 
Orthosis with stance phase control knee joint

Paralysis, length differences and deformations of the lower extremities can lead to a hindrance when walking with compensation mechanisms that lead to a severe impairment of the gait pattern. In order to be able to stand and walk safely and to improve the gait pattern, orthotics can be included in the therapy concept. Today, modern materials and functional elements enable the orthosis to be specifically adapted to the requirements resulting from the patient's gait. Mechanical stance phase control knee joints may secure the knee joint in the early stance phases and release again for knee flexion when the swing phase is initiated. With the help of an orthotic treatment with a stance phase control knee joint, a natural gait pattern can be achieved despite mechanical protection against unwanted knee flexion. In these cases, locked knee joints are often used, which have a good safety function, but do not allow knee flexion when walking during swing phase. With such joints, the knee joint remains mechanically blocked during the swing phase. Patients with locked knee joints must swing the leg forward with the knee extended even during the swing phase. This only works if the patient develops compensatory mechanisms, e.g. by raising the body's center of gravity in the swing phase (Duchenne limping) or by swinging the orthotic leg to the side (circumduction).[84][85][86]

Epidemiology

Reported polio cases in 2019'[87][88]
 
Country Wild
cases
Circulating
vaccine-
derived
cases (cVDPV)
Transmission
status
Type
  Pakistan 147 22 endemic WPV1
cVDPV2
  Afghanistan 29 0 endemic WPV1
  Angola 0 129 cVDPV only cVDPV2
  DRC 0 86 cVDPV only cVDPV2
  CAR 0 19 cVDPV only cVDPV2
  Ghana 0 18 cVDPV only cVDPV2
  Nigeria 0 18 cVDPV only cVDPV2
  Philippines 0 15 cVDPV only cVDPV1
cVDPV2
  Ethiopia 0 12 cVDPV only cVDPV2
  Chad 0 9 cVDPV only cVDPV2
  Benin 0 8 cVDPV only cVDPV2
  Togo 0 8 cVDPV only cVDPV2
  Myanmar 0 6 cVDPV only cVDPV1
  Somalia 0 3 cVDPV only cVDPV2
  Malaysia 0 3 cVDPV only cVDPV1
  Zambia 0 2 cVDPV only cVDPV2
  Burkina Faso 0 1 cVDPV only cVDPV2
  China 0 1 cVDPV only cVDPV2
  Niger 0 1 cVDPV only cVDPV2
  Yemen 0 3 cVDPV only cVDPV1
Total 175 365
 
The decade of the last recorded case of paralytic polio. Since the creation of this image, Nigeria has been certified free of wild polio as of August 2020 and one case was recorded in the US state of New York in July 2022.[89]

Eradication

Following the widespread use of poliovirus vaccine in the mid-1950s, new cases of poliomyelitis declined dramatically in many industrialized countries. A global effort to eradicate polio - the Global Polio Eradication Initiative - began in 1988, led by the World Health Organization, UNICEF, and The Rotary Foundation.[90] Polio is one of only two diseases currently the subject of a global eradication program, the other being Guinea worm disease.[91] So far, the only diseases completely eradicated by humankind are smallpox, declared eradicated in 1980,[92][93] and rinderpest, declared eradicated in 2011.[94] In April 2012, the World Health Assembly declared that the failure to completely eradicate polio would be a programmatic emergency for global public health, and that it "must not happen."[95]

These efforts have hugely reduced the number of cases; 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.[96][97]

By 2015, polio was believed to remain naturally spreading in only two countries, Pakistan and Afghanistan,[98][99][100][101] although it continued to cause outbreaks in other nearby countries due to hidden or reestablished transmission.[102] Between 2016 and 2020 worldwide cases of wild polio (mostly in these countries) remained below 200 per year, with only 6 confirmed cases in 2021.[10]

Circulating vaccine-derived polioviruses

The oral polio vaccine, while highly effective, has the disadvantage that it comprises a live virus which has been attenuated so that it cannot cause severe illness. The vaccine virus is excreted in the stool, and in under-immunized communities it can spread from person to person. This is known as circulating vaccine-derived poliovirus (cVDPV).

With prolonged transmission of this kind the weakened virus can mutate and revert to a form that causes illness and paralysis. Cases of cVDPV now exceed wild-type cases, making it desirable to discontinue the use of the oral polio vaccine as soon as safely possible and instead use other types of polio vaccines.[11][103]

Afghanistan and Pakistan

The last remaining region with wild polio cases are the South Asian countries Afghanistan and Pakistan.

During 2011, the CIA ran a fake hepatitis vaccination clinic in Abbottabad, Pakistan in an attempt to locate Osama bin Laden. This destroyed trust in vaccination programs in the region.[104][105] There were attacks and deaths among vaccination workers; 66 vaccinators were killed in 2013 and 2014.[106][107] In Afghanistan, the Taliban banned house-to-house polio vaccination between 2018 and 2021.[108] These factors have set back efforts to eliminate polio by means of vaccination in these countries.[109]

In Afghanistan, 80 cases of polio were reported from 35 districts during 2011. Incidence over the subsequent 10 years has declined to just 4 cases in 2 districts during 2021.[110][111]

In Pakistan, cases dropped by 97 percent from 2014 to 2018;[112] reasons include 440 million dirham support from the United Arab Emirates to vaccinate more than ten million children,[107][113] changes in the military situation, and arrests of some of those who attacked polio workers.[114][115] During 2021 only one case of wild polio was detected in Pakistan.[10]

Americas

The Americas were declared polio-free in 1994.[116] The last known case was a boy in Peru in 1991.[117] The US Centers for Disease Control and Prevention recommends polio vaccination boosters for travelers and those who live in countries where the disease is endemic.[118]

In July 2022, the US state of New York reported a polio case for the first time in almost a decade in the country. Health officials said the person, an unvaccinated young adult who had not recently travelled abroad, first showed symptoms a month earlier and eventually developed paralysis; this was subsequently attributed to a vaccine-derived strain of the virus.[119] In October, the CDC reported detection of vaccine-derived virus in wastewater samples collected from five New York counties.[120][121]

Western Pacific

In 2000, polio was declared to have been officially eliminated in 37 Western Pacific countries, including China and Australia.[122][123]

Despite eradication ten years earlier, an outbreak was confirmed in China in September 2011, involving a strain common in Pakistan.[124]

In September 2019, the Department of Health of the Philippines declared a polio outbreak in the country after a single case in a 3-year-old girl.[125] The outbreak was declared to be ended during June 2021.[126] In December 2019, acute poliomyelitis was confirmed in an infant in Sabah state, Borneo, Malaysia.[127] Subsequently, a further three polio cases were reported, with the last case reported in January 2020. Prior to this, Malaysia had been declared polio-free in 2000. WHO declared an end to the outbreak in September 2021.[128] Both outbreaks were found to be linked instances of vaccine-derived poliomyelitis.[129]

Europe

Europe was declared polio-free in 2002.[130]

Southeast Asia

The last case of polio in the region was in India (part of the WHO's South-East Asia Region) in January 2011.[131] 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.[132][133]

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, India, Indonesia, Maldives, Myanmar, Nepal, Sri Lanka, Thailand and Timor-Leste.[98] With the addition of this region, 80 per cent of the world population was considered to be living in polio-free regions.[98]

Middle East

In Syria difficulties in executing immunization programs in the ongoing civil war led to a return of polio, probably in 2012,[134] acknowledged by the WHO in 2013.[135][136] 15 cases were confirmed among children in Syria between October and November 2013 in Deir Ezzor. Later, two more cases, one each in rural 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.[137] A vaccination campaign in Syria operated literally under fire and led to the deaths of several vaccinators,[138] but returned vaccination coverage to pre-war levels.[139]

An outbreak of vaccine-derived polio was confirmed in 2017 in eastern Syria.[140][141] Syria is currently free of polio, but is consider "at risk".[142]

Africa

 
Polio vaccination in Egypt

In 2003 in northern Nigeria – a country which at that time was considered provisionally polio free – a fatwa was issued declaring that the polio vaccine was designed to render children sterile.[143] 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.[144][145] Local traditional and religious leaders and polio survivors worked to revive the campaign,[146] and Nigeria was removed from the polio-endemic list in September 2015 after more than a year without any cases,[147] only to be restored to the list in 2016 when two cases were detected.[148]

Africa was declared free of wild polio in August 2020, although cases of circulating vaccine-derived poliovirus type 2 continue to appear in several countries.[149]

A single case of wild polio which was detected in Malawi in February 2022, and another in Mozambique in May 2022 were both of a strain imported from Pakistan and do not affect the African region's wild poliovirus-free certification status.[150][151]

History

 
An Egyptian stele thought to represent a person with polio, 18th Dynasty (1403–1365 BC)

The effects of polio have been known since prehistory; Egyptian paintings and carvings depict otherwise healthy people with withered limbs, and young children walking with canes.[152] 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".[153] The work of physicians Jakob Heine in 1840 and Karl Oskar Medin in 1890 led to it being known as Heine–Medin disease.[154] 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 sanitation of the time resulted in constant exposure to the virus, which enhanced a natural immunity within the population. In developed countries during the late 19th and early 20th centuries, improvements were made in community sanitation, including better 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.[155]

Small localized paralytic polio epidemics began to appear in Europe and the United States around 1900.[156] 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.[157] Accordingly, the rate of paralysis and death due to polio infection also increased during this time.[156] 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.[158] Intensive care medicine has its origin in the fight against polio.[159] Most hospitals in the 1950s had limited access to iron lungs 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 Copenhagen by Danish anesthesiologist Bjørn Ibsen, were the precursors of modern intensive care units (ICU). (A year later, Ibsen would establish the world's first dedicated ICU.)[160]

The polio epidemics not only altered the lives of those who survived them, but also brought profound cultural changes, spurring grassroots fund-raising campaigns that would revolutionize medical philanthropy, and giving rise to the modern field of 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.[161] In 1977, there were 254,000 persons living in the United States who had been paralyzed by polio.[162] According to doctors and local polio support groups, some 40,000 polio survivors with varying degrees of paralysis were living 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 in 2001.[161] 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.[163]

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.[164][165]

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 Global Polio Eradication Initiative (GPEI) in 1988. Since then, GPEI has reduced polio worldwide by 99 percent.[166]

Etymology

The term derives from the Ancient Greek poliós (πολιός), meaning "grey", myelós (µυελός "marrow"), referring to the grey matter of the spinal cord, and the suffix -itis, which denotes inflammation,[13] 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 polioencephalitis, resulting in inability to breathe, requiring mechanical assistance such as an 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.[167][168] Pocapavir (a capsid inhibitor) and V-7404 (a protease inhibitor) may speed up viral clearance and are being studied for this purpose.[169]

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Further reading

External video
  Presentation by David Oshinsky on Polio, June 21, 2006, C-SPAN
  Presentation by Oshinsky on Polio, October 8, 2006, C-SPAN
  • Kluger Jefferey (2004). Splendid Solution: Jonas Salk and the Conquest of Polio. New York: G. P. Putnam's Sons. ISBN 978-0-399-15216-0.
  • Oshinsky DM (2005). Polio: An American story. Oxford: Oxford University Press. ISBN 978-0-19-515294-4. polio.
  • Shaffer MM, Bernard S (2005). The death of a disease: a history of the eradication of poliomyelitis. New Brunswick, NJ: Rutgers University Press. ISBN 978-0-8135-3677-4.
  • Shell M (2005). Polio and its aftermath: the paralysis of culture. Cambridge: Harvard University Press. ISBN 978-0-674-01315-5. polio.
  • Wilson DJ (2005). Living with polio: the epidemic and its survivors. Chicago: University of Chicago Press. ISBN 978-0-226-90103-9.
  • Wilson DJ, Silver J (2007). Polio voices: an oral history from the American polio epidemics and worldwide eradication efforts. New York: Praeger. ISBN 978-0-275-99492-1.

External links

  •   Media related to Polio at Wikimedia Commons
  •   Quotations related to Polio at Wikiquote
  •   The dictionary definition of polio at Wiktionary
  • Polio at Curlie

polio, myelitis, redirects, here, virus, virus, other, uses, disambiguation, myelitis, commonly, shortened, polio, infectious, disease, caused, poliovirus, approximately, cases, asymptomatic, mild, symptoms, which, occur, include, sore, throat, fever, proporti. Poliomyelitis redirects here For the virus see Poliovirus For other uses see Polio disambiguation Poliomyelitis commonly shortened to polio is an infectious disease caused by the poliovirus 1 Approximately 70 of cases are asymptomatic mild symptoms which can occur include sore throat and fever in a proportion of cases more severe symptoms develop such as headache neck stiffness and paresthesia 1 3 These symptoms usually pass within one or two weeks 1 A less common symptom is permanent paralysis and possible death in extreme cases 1 Years after recovery post polio syndrome may occur with a slow development of muscle weakness similar to that which the person had during the initial infection 2 PolioOther namesPoliomyelitis infantile paralysis Heine Medin diseaseA man with a wasted right leg due to poliomyelitisPronunciation ˌ p oʊ l i oʊ ˌ m aɪ e ˈ l aɪ t ɪ s SpecialtyNeurology Infectious diseaseSymptomsFever sore throat 1 ComplicationsMuscle weakness resulting in paralysis 1 Post polio syndrome 2 TypesWild PV types 1 2 amp 3 vaccine derived PV 1 CausesPoliovirus spread by fecal oral route 1 Risk factorsPoor hygieneDiagnostic methodFinding the virus in the feces or antibodies in the blood 1 PreventionPolio vaccine 3 TreatmentNo treatment other than supportive care 3 Frequency6 wild 691 vaccine derived in 2021 4 Polio occurs naturally only in humans 1 It is highly infectious and is spread from person to person either through fecal oral transmission 1 5 e g poor hygiene or by ingestion of food or water contaminated by human feces or via the oral oral route 1 Those who are infected may spread the disease for up to six weeks even if no symptoms are present 1 The disease may be diagnosed by finding the virus in the feces or detecting antibodies against it in the blood 1 Poliomyelitis has existed for thousands of years with depictions of the disease in ancient art 1 The disease was first recognized as a distinct condition by the English physician Michael Underwood in 1789 1 6 and the virus that causes it was first identified in 1909 by the Austrian immunologist Karl Landsteiner 7 8 Major outbreaks started to occur in the late 19th century in Europe and the United States 1 and in the 20th century it became one of the most worrying childhood diseases 9 Following the introduction of polio vaccines in the 1950s polio incidence declined rapidly 1 Once infected there is no specific treatment 3 The disease can be prevented by the polio vaccine with multiple doses required for lifelong protection 3 There are two broad types of polio vaccine an injected vaccine using inactivated poliovirus and an oral vaccine containing attenuated weakened live virus 1 Through the use of both types of vaccine incidence of wild polio has decreased from an estimated 350 000 cases in 1988 3 to 6 confirmed cases in 2021 confined to just three countries 10 There are rare incidents of disease transmission and or of paralytic polio associated with the attenuated oral vaccine and for this reason the injected vaccine is preferred 11 Contents 1 Signs and symptoms 2 Cause 2 1 Transmission 3 Pathophysiology 3 1 Paralytic polio 3 1 1 Spinal polio 3 1 2 Bulbar polio 3 1 3 Bulbospinal polio 4 Diagnosis 5 Prevention 5 1 Passive immunization 5 2 Vaccine 6 Treatment 7 Prognosis 7 1 Recovery 7 2 Complications 7 3 Post polio syndrome 8 Orthotics 9 Epidemiology 9 1 Eradication 9 2 Circulating vaccine derived polioviruses 9 3 Afghanistan and Pakistan 9 4 Americas 9 5 Western Pacific 9 6 Europe 9 7 Southeast Asia 9 8 Middle East 9 9 Africa 10 History 10 1 Etymology 11 Research 12 References 13 Further reading 14 External linksSigns and symptomsOutcomes of poliovirus infection in children Outcome Proportion of cases 1 No symptoms 72 Minor illness 24 Nonparalytic aseptic meningitis 1 5 Paralytic poliomyelitis 0 1 0 5 Spinal polio 79 of paralytic cases Bulbospinal polio 19 of paralytic cases Bulbar polio 2 of paralytic casesThe 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 central nervous system CNS sometimes called abortive poliomyelitis and a major illness involving the CNS which may be paralytic or nonparalytic 12 Adults are more likely to develop symptoms including severe symptoms than children 1 In most people with a normal immune system a poliovirus infection is asymptomatic In about 25 of cases the infection produces minor symptoms which may include sore throat and low fever 3 These symptoms are temporary and full recovery occurs within one or two weeks 1 3 In about 1 percent of infections the virus can migrate from the gastrointestinal tract into the central nervous system CNS 1 Most patients with CNS involvement develop nonparalytic aseptic meningitis with symptoms of headache neck back abdominal and extremity pain fever vomiting stomach pain lethargy and irritability 13 14 15 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 16 The weakness most often involves the legs but may less commonly involve the muscles of the head neck and diaphragm 1 Depending on the site of paralysis paralytic poliomyelitis is classified as spinal bulbar or bulbospinal In those who develop paralysis between 2 and 10 percent die as the paralysis affects the breathing muscles 3 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 seizures and spastic paralysis 17 CauseMain article Poliovirus A TEM micrograph of poliovirus Poliomyelitis is caused by infection with a member of the genus Enterovirus known as poliovirus PV This group of RNA viruses colonize the gastrointestinal tract 18 specifically the oropharynx and the intestine The incubation time form the first signs and symptoms ranges from three to 35 days with a more common span of six to 20 days 1 PV does not affect any species other than humans 19 Its structure is quite simple composed of a single sense RNA genome enclosed in a protein shell called a capsid 19 In addition to protecting the virus genetic material the capsid proteins enable poliovirus to infect certain types of cells Three serotypes of poliovirus have been identified wild poliovirus type 1 WPV1 type 2 WPV2 and type 3 WPV3 each with a slightly different capsid protein 20 All three are extremely virulent and produce the same disease symptoms 19 PV1 is the most commonly encountered form and the one most closely associated with paralysis 21 WPV2 was certified as eradicated in 2015 and WPV3 certified as eradicated in 2019 22 Individuals who are exposed to the virus either through infection or by immunization via polio vaccine develop immunity In immune individuals IgA antibodies against poliovirus are present in the tonsils and gastrointestinal tract and able to block virus replication IgG and IgM antibodies against PV can prevent the spread of the virus to motor neurons of the central nervous system 23 Infection or vaccination with one serotype of poliovirus does not provide immunity against the other serotypes and full immunity requires exposure to each serotype 23 A rare condition with a similar presentation nonpoliovirus poliomyelitis may result from infections with enteroviruses other than poliovirus 24 The oral polio vaccine contains weakened viruses that can replicate On rare occasions these may be transmitted from the vaccinated person to other people who may display symptoms of polio In communities with good vaccine coverage transmission is limited and the virus dies out In communities with low vaccine coverage this weakened virus may continue to circulate 25 Polio arising from this cause is referred to as circulating vaccine derived polio cVDPV in order to distinguish it from the natural or wild poliovirus WPV 26 Transmission Poliomyelitis is highly contagious via the fecal oral intestinal source and the oral oral oropharyngeal source routes 23 In endemic areas wild polioviruses can infect virtually the entire human population 27 It is seasonal in temperate climates with peak transmission occurring in summer and autumn 23 These seasonal differences are far less pronounced in tropical areas 27 The time between first exposure and first symptoms known as the incubation period is usually 6 to 20 days with a maximum range of 3 to 35 days 28 Virus particles are excreted in the feces for several weeks following initial infection 28 The disease is transmitted primarily via the fecal oral route by ingesting contaminated food or water It is occasionally transmitted via the oral oral route 21 a mode especially visible in areas with good sanitation and hygiene 23 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 21 Factors that increase the risk of polio infection or affect the severity of the disease include immune deficiency 29 malnutrition 30 physical activity immediately following the onset of paralysis 31 skeletal muscle injury due to injection of vaccines or therapeutic agents 32 and pregnancy 33 Although the virus can cross the maternal fetal barrier during pregnancy the fetus does not appear to be affected by either maternal infection or polio vaccination 34 Maternal antibodies also cross the placenta providing passive immunity that protects the infant from polio infection during the first few months of life 35 Pathophysiology A photomicrograph of the lumbar spinal cord depicting an infarct due to Polio Type III surrounding the anterior spinal artery 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 CD155 on the cell membrane 36 The virus then hijacks the host cell s own machinery and begins to 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 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 37 Known as 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 38 In a small percentage of cases it can spread and replicate in other sites such as brown fat the reticuloendothelial tissues and muscle 39 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 meninges the layers of tissue surrounding the brain which is known as nonparalytic aseptic meningitis 13 Penetration of the CNS provides no known benefit to the virus and is quite possibly an incidental deviation of a normal gastrointestinal infection 40 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 40 Paralytic polio Denervation of skeletal muscle tissue secondary to poliovirus infection can lead to paralysis In around one percent of infections poliovirus spreads along certain nerve fiber pathways preferentially replicating in and destroying motor neurons within the spinal cord brain stem or 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 lesions within the spinal ganglia these may also occur in the reticular formation vestibular nuclei cerebellar vermis and deep cerebellar nuclei 40 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 13 Other destructive changes associated with paralytic disease occur in the forebrain region specifically the hypothalamus and thalamus 40 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 muscle pain loss of superficial and deep reflexes 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 41 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 42 In children under five years of age paralysis of one leg is most common in adults extensive paralysis of the chest and abdomen also affecting all four limbs quadriplegia is more likely 43 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 44 Spinal polio 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 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 16 Virus invasion causes inflammation of the nerve cells leading to damage or destruction of motor neuron ganglia When spinal neurons die Wallerian degeneration takes place leading to weakness of those muscles formerly innervated by the now dead neurons 45 With the destruction of nerve cells the muscles no longer receive signals from the brain or spinal cord without nerve stimulation the muscles atrophy becoming weak floppy and poorly controlled and finally completely paralyzed 16 Maximum paralysis progresses rapidly two to four days and usually involves fever and muscle pain Deep tendon reflexes are also affected and are typically absent or diminished sensation the ability to feel in the paralyzed limbs however is not affected 46 The extent of spinal paralysis depends on the region of the cord affected which may be cervical thoracic or lumbar 47 The virus may affect muscles on both sides of the body but more often the paralysis is asymmetrical 37 Any limb or combination of limbs may be affected one leg one arm or both legs and both arms Paralysis is often more severe proximally where the limb joins the body than distally the fingertips and toes 37 Bulbar polio The location and anatomy of the bulbar region in orange Making up about two percent of cases of paralytic polio bulbar polio occurs when poliovirus invades and destroys nerves within the bulbar region of the brain stem 1 The bulbar region is a white matter pathway that connects the cerebral cortex to the brain stem The destruction of these nerves weakens the muscles supplied by the cranial nerves producing symptoms of encephalitis and causes difficulty breathing speaking and swallowing 15 Critical nerves affected are the glossopharyngeal nerve which partially controls swallowing and functions in the throat tongue movement and taste the vagus nerve which sends signals to the heart intestines and lungs and the accessory nerve which controls upper neck movement Due to the effect on swallowing secretions of mucus may build up in the airway causing suffocation 41 Other signs and symptoms include facial weakness caused by destruction of the trigeminal nerve and facial nerve which innervate the cheeks tear ducts gums and muscles of the face among other structures double vision difficulty in chewing and abnormal respiratory rate depth and rhythm which may lead to respiratory arrest Pulmonary edema and shock are also possible and may be fatal 47 Bulbospinal polio Approximately 19 percent of all paralytic polio cases have both bulbar and spinal symptoms this subtype is called respiratory or bulbospinal polio 1 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 ventilator It can lead to paralysis of the arms and legs and may also affect swallowing and heart functions 48 DiagnosisParalytic 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 49 A laboratory diagnosis is usually made based on the recovery of poliovirus from a stool sample or a swab of the pharynx Antibodies to poliovirus can be diagnostic and are generally detected in the blood of infected patients early in the course of infection 1 Analysis of the patient s cerebrospinal fluid CSF which is collected by a lumbar puncture spinal tap reveals an increased number of white blood cells primarily lymphocytes and a mildly elevated protein level Detection of virus in the CSF is diagnostic of paralytic polio but rarely occurs 1 If poliovirus is isolated from a patient experiencing acute flaccid paralysis it is further tested through oligonucleotide mapping genetic fingerprinting or more recently by PCR amplification to determine whether it is wild type that is the virus encountered in nature or vaccine type derived from a strain of poliovirus used to produce polio vaccine 50 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 asymptomatic carriers exist 51 PreventionPassive immunization In 1950 William Hammon at the University of Pittsburgh purified the gamma globulin component of the blood plasma of polio survivors 52 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 clinical trial were promising the gamma globulin was shown to be about 80 percent effective in preventing the development of paralytic poliomyelitis 53 It was also shown to reduce the severity of the disease in patients who developed polio 52 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 54 Vaccine Main article Polio vaccine 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 and are effective in protecting individuals from disease The first candidate polio vaccine based on one serotype of a live but 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 55 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 56 The second polio virus vaccine was developed in 1952 by Jonas Salk at the University of Pittsburgh and announced to the world on 12 April 1955 57 58 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 23 After two doses of inactivated poliovirus vaccine given by injection 90 percent or more of individuals develop protective antibody to all three serotypes of poliovirus and at least 99 percent are immune to poliovirus following three doses 1 Subsequently Albert Sabin developed another live oral polio vaccine OPV It was produced by the repeated passage of the virus through nonhuman cells at subphysiological temperatures 59 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 60 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 1 Human trials of Sabin s vaccine began in 1957 61 and in 1958 it was selected in competition with the live vaccines of Koprowski and other researchers by the US National Institutes of Health 56 Licensed in 1962 61 it rapidly became the only polio vaccine used worldwide 56 OPV efficiently blocks person to person transmission of wild poliovirus by oral oral and fecal oral routes thereby protecting both individual vaccine recipients and the wider community herd immunity 62 IPV confers good immunity but is less effective at preventing spread of wild poliovirus by the fecal oral route 63 Wild polio vs cVDVP cases 2000 2019 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 endemic it has been the vaccine of choice for controlling poliomyelitis in many countries 64 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 28 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 65 Most 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 66 TreatmentThere is no cure for polio but there are treatments 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 67 Treatment of polio often requires long term rehabilitation including occupational therapy physical therapy braces corrective shoes and in some cases orthopedic surgery 47 Portable ventilators 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 worn over the chest and abdomen 68 Other historical treatments for polio include hydrotherapy electrotherapy massage and passive motion exercises and surgical treatments such as tendon lengthening and nerve grafting 16 Sister Elizabeth Kenny s Kenny regimen is now the hallmark for the treatment of paralytic polio 69 Prognosis A girl with genu recurvatum 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 70 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 70 Half the patients with spinal polio recover fully one quarter recover with mild disability and the remaining quarter are left with severe disability 71 The degree of both acute paralysis and residual paralysis is likely to be proportional to the degree of viremia and inversely proportional to the degree of immunity 40 Spinal polio is rarely fatal 41 Without respiratory support consequences of poliomyelitis with respiratory involvement include suffocation or pneumonia from aspiration of secretions 68 Overall 5 to 10 percent of patients with paralytic polio die due to the paralysis of muscles used for breathing The case fatality rate CFR varies by age 2 to 5 percent of children and up to 15 to 30 percent of adults die 1 Bulbar polio often causes death if respiratory support is not provided 48 with support its CFR ranges from 25 to 75 percent depending on the age of the patient 1 72 When intermittent positive pressure ventilation is available the fatalities can be reduced to 15 percent 73 Recovery Many cases of poliomyelitis result in only temporary paralysis 16 Generally in these cases nerve impulses return to the paralyzed muscle within a month and recovery is complete in six to eight months 70 The 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 74 Paralysis remaining after one year is likely to be permanent although some recovery of muscle strength is possible up to 18 months after infection 70 One mechanism involved in recovery is nerve terminal sprouting in which remaining brainstem and spinal cord motor neurons develop new branches or axonal sprouts 75 These sprouts can reinnervate orphaned muscle fibers that have been denervated by acute polio infection 76 restoring the fibers capacity to contract and improving strength 77 Terminal sprouting may generate a few significantly enlarged motor neurons doing work previously performed by as many as four or five units 42 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 myofiber hypertrophy enlargement of muscle fibers through exercise and activity and transformation of type II muscle fibers to type I muscle fibers 76 78 In addition to these physiological processes the body can compensate for residual paralysis in other ways Weaker muscles can be used at a higher than usual intensity relative to the muscle s maximal capacity little used muscles can be developed and ligaments can enable stability and mobility 78 Complications Residual complications of paralytic polio often occur following the initial recovery process 15 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 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 Achilles tendons at the back of the foot retract and the foot cannot take on a normal position People with polio that develop equinus foot cannot walk properly because they cannot put their heels on the ground A similar situation can develop if the arms become paralyzed 79 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 79 Osteoporosis and increased likelihood of bone fractures may occur An intervention to prevent or lessen length disparity can be to perform an epiphysiodesis on the distal femoral and proximal tibial fibular condyles so that limb s growth is artificially stunted and by the time of 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 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 48 80 Complications from prolonged immobility involving the lungs kidneys and heart include pulmonary edema aspiration pneumonia urinary tract infections kidney stones paralytic ileus myocarditis and cor pulmonale 48 80 Post polio syndrome Main article 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 81 notably new muscle weakness and extreme fatigue This condition is known as post polio syndrome PPS or post polio sequelae 77 The symptoms of PPS are thought to involve a failure of the oversized motor units created during the recovery phase of the paralytic disease 82 83 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 77 Post polio syndrome is not an infectious process and persons experiencing the syndrome do not shed poliovirus 1 Orthotics Orthosis with stance phase control knee joint Paralysis length differences and deformations of the lower extremities can lead to a hindrance when walking with compensation mechanisms that lead to a severe impairment of the gait pattern In order to be able to stand and walk safely and to improve the gait pattern orthotics can be included in the therapy concept Today modern materials and functional elements enable the orthosis to be specifically adapted to the requirements resulting from the patient s gait Mechanical stance phase control knee joints may secure the knee joint in the early stance phases and release again for knee flexion when the swing phase is initiated With the help of an orthotic treatment with a stance phase control knee joint a natural gait pattern can be achieved despite mechanical protection against unwanted knee flexion In these cases locked knee joints are often used which have a good safety function but do not allow knee flexion when walking during swing phase With such joints the knee joint remains mechanically blocked during the swing phase Patients with locked knee joints must swing the leg forward with the knee extended even during the swing phase This only works if the patient develops compensatory mechanisms e g by raising the body s center of gravity in the swing phase Duchenne limping or by swinging the orthotic leg to the side circumduction 84 85 86 EpidemiologyReported polio cases in 2019 87 88 Country Wildcases Circulatingvaccine derivedcases cVDPV Transmissionstatus Type Pakistan 147 22 endemic WPV1 cVDPV2 Afghanistan 29 0 endemic WPV1 Angola 0 129 cVDPV only cVDPV2 DRC 0 86 cVDPV only cVDPV2 CAR 0 19 cVDPV only cVDPV2 Ghana 0 18 cVDPV only cVDPV2 Nigeria 0 18 cVDPV only cVDPV2 Philippines 0 15 cVDPV only cVDPV1cVDPV2 Ethiopia 0 12 cVDPV only cVDPV2 Chad 0 9 cVDPV only cVDPV2 Benin 0 8 cVDPV only cVDPV2 Togo 0 8 cVDPV only cVDPV2 Myanmar 0 6 cVDPV only cVDPV1 Somalia 0 3 cVDPV only cVDPV2 Malaysia 0 3 cVDPV only cVDPV1 Zambia 0 2 cVDPV only cVDPV2 Burkina Faso 0 1 cVDPV only cVDPV2 China 0 1 cVDPV only cVDPV2 Niger 0 1 cVDPV only cVDPV2 Yemen 0 3 cVDPV only cVDPV1Total 175 365 The decade of the last recorded case of paralytic polio Since the creation of this image Nigeria has been certified free of wild polio as of August 2020 and one case was recorded in the US state of New York in July 2022 89 Eradication See also Poliomyelitis eradication Following the widespread use of poliovirus vaccine in the mid 1950s new cases of poliomyelitis declined dramatically in many industrialized countries A global effort to eradicate polio the Global Polio Eradication Initiative began in 1988 led by the World Health Organization UNICEF and The Rotary Foundation 90 Polio is one of only two diseases currently the subject of a global eradication program the other being Guinea worm disease 91 So far the only diseases completely eradicated by humankind are smallpox declared eradicated in 1980 92 93 and rinderpest declared eradicated in 2011 94 In April 2012 the World Health Assembly declared that the failure to completely eradicate polio would be a programmatic emergency for global public health and that it must not happen 95 These efforts have hugely reduced the number of cases 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 96 97 By 2015 polio was believed to remain naturally spreading in only two countries Pakistan and Afghanistan 98 99 100 101 although it continued to cause outbreaks in other nearby countries due to hidden or reestablished transmission 102 Between 2016 and 2020 worldwide cases of wild polio mostly in these countries remained below 200 per year with only 6 confirmed cases in 2021 10 Circulating vaccine derived polioviruses The oral polio vaccine while highly effective has the disadvantage that it comprises a live virus which has been attenuated so that it cannot cause severe illness The vaccine virus is excreted in the stool and in under immunized communities it can spread from person to person This is known as circulating vaccine derived poliovirus cVDPV With prolonged transmission of this kind the weakened virus can mutate and revert to a form that causes illness and paralysis Cases of cVDPV now exceed wild type cases making it desirable to discontinue the use of the oral polio vaccine as soon as safely possible and instead use other types of polio vaccines 11 103 Afghanistan and Pakistan See also Polio in Pakistan The last remaining region with wild polio cases are the South Asian countries Afghanistan and Pakistan During 2011 the CIA ran a fake hepatitis vaccination clinic in Abbottabad Pakistan in an attempt to locate Osama bin Laden This destroyed trust in vaccination programs in the region 104 105 There were attacks and deaths among vaccination workers 66 vaccinators were killed in 2013 and 2014 106 107 In Afghanistan the Taliban banned house to house polio vaccination between 2018 and 2021 108 These factors have set back efforts to eliminate polio by means of vaccination in these countries 109 In Afghanistan 80 cases of polio were reported from 35 districts during 2011 Incidence over the subsequent 10 years has declined to just 4 cases in 2 districts during 2021 110 111 In Pakistan cases dropped by 97 percent from 2014 to 2018 112 reasons include 440 million dirham support from the United Arab Emirates to vaccinate more than ten million children 107 113 changes in the military situation and arrests of some of those who attacked polio workers 114 115 During 2021 only one case of wild polio was detected in Pakistan 10 Americas The Americas were declared polio free in 1994 116 The last known case was a boy in Peru in 1991 117 The US Centers for Disease Control and Prevention recommends polio vaccination boosters for travelers and those who live in countries where the disease is endemic 118 In July 2022 the US state of New York reported a polio case for the first time in almost a decade in the country Health officials said the person an unvaccinated young adult who had not recently travelled abroad first showed symptoms a month earlier and eventually developed paralysis this was subsequently attributed to a vaccine derived strain of the virus 119 In October the CDC reported detection of vaccine derived virus in wastewater samples collected from five New York counties 120 121 Western Pacific In 2000 polio was declared to have been officially eliminated in 37 Western Pacific countries including China and Australia 122 123 Despite eradication ten years earlier an outbreak was confirmed in China in September 2011 involving a strain common in Pakistan 124 In September 2019 the Department of Health of the Philippines declared a polio outbreak in the country after a single case in a 3 year old girl 125 The outbreak was declared to be ended during June 2021 126 In December 2019 acute poliomyelitis was confirmed in an infant in Sabah state Borneo Malaysia 127 Subsequently a further three polio cases were reported with the last case reported in January 2020 Prior to this Malaysia had been declared polio free in 2000 WHO declared an end to the outbreak in September 2021 128 Both outbreaks were found to be linked instances of vaccine derived poliomyelitis 129 Europe Europe was declared polio free in 2002 130 Southeast Asia The last case of polio in the region was in India part of the WHO s South East Asia Region in January 2011 131 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 132 133 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 India Indonesia Maldives Myanmar Nepal Sri Lanka Thailand and Timor Leste 98 With the addition of this region 80 per cent of the world population was considered to be living in polio free regions 98 Middle East In Syria difficulties in executing immunization programs in the ongoing civil war led to a return of polio probably in 2012 134 acknowledged by the WHO in 2013 135 136 15 cases were confirmed among children in Syria between October and November 2013 in Deir Ezzor Later two more cases one each in rural 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 137 A vaccination campaign in Syria operated literally under fire and led to the deaths of several vaccinators 138 but returned vaccination coverage to pre war levels 139 An outbreak of vaccine derived polio was confirmed in 2017 in eastern Syria 140 141 Syria is currently free of polio but is consider at risk 142 Africa Polio vaccination in Egypt In 2003 in northern Nigeria a country which at that time was considered provisionally polio free a fatwa was issued declaring that the polio vaccine was designed to render children sterile 143 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 144 145 Local traditional and religious leaders and polio survivors worked to revive the campaign 146 and Nigeria was removed from the polio endemic list in September 2015 after more than a year without any cases 147 only to be restored to the list in 2016 when two cases were detected 148 Africa was declared free of wild polio in August 2020 although cases of circulating vaccine derived poliovirus type 2 continue to appear in several countries 149 A single case of wild polio which was detected in Malawi in February 2022 and another in Mozambique in May 2022 were both of a strain imported from Pakistan and do not affect the African region s wild poliovirus free certification status 150 151 HistorySee also History of poliomyelitis and List of poliomyelitis survivors An Egyptian stele thought to represent a person with polio 18th Dynasty 1403 1365 BC The effects of polio have been known since prehistory Egyptian paintings and carvings depict otherwise healthy people with withered limbs and young children walking with canes 152 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 153 The work of physicians Jakob Heine in 1840 and Karl Oskar Medin in 1890 led to it being known as Heine Medin disease 154 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 sanitation of the time resulted in constant exposure to the virus which enhanced a natural immunity within the population In developed countries during the late 19th and early 20th centuries improvements were made in community sanitation including better 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 155 Small localized paralytic polio epidemics began to appear in Europe and the United States around 1900 156 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 157 Accordingly the rate of paralysis and death due to polio infection also increased during this time 156 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 158 Intensive care medicine has its origin in the fight against polio 159 Most hospitals in the 1950s had limited access to iron lungs 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 Copenhagen by Danish anesthesiologist Bjorn Ibsen were the precursors of modern intensive care units ICU A year later Ibsen would establish the world s first dedicated ICU 160 The polio epidemics not only altered the lives of those who survived them but also brought profound cultural changes spurring grassroots fund raising campaigns that would revolutionize medical philanthropy and giving rise to the modern field of 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 161 In 1977 there were 254 000 persons living in the United States who had been paralyzed by polio 162 According to doctors and local polio support groups some 40 000 polio survivors with varying degrees of paralysis were living 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 in 2001 161 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 163 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 164 165 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 Global Polio Eradication Initiative GPEI in 1988 Since then GPEI has reduced polio worldwide by 99 percent 166 Etymology The term derives from the Ancient Greek polios polios meaning grey myelos µyelos marrow referring to the grey matter of the spinal cord and the suffix itis which denotes inflammation 13 i e inflammation of the spinal cord s grey matter although a severe infection can extend into the brainstem and even 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Cambridge Harvard University Press ISBN 978 0 674 01315 5 polio Wilson DJ 2005 Living with polio the epidemic and its survivors Chicago University of Chicago Press ISBN 978 0 226 90103 9 Wilson DJ Silver J 2007 Polio voices an oral history from the American polio epidemics and worldwide eradication efforts New York Praeger ISBN 978 0 275 99492 1 External links Medicine portal Viruses portal Media related to Polio at Wikimedia Commons Quotations related to Polio at Wikiquote The dictionary definition of polio at Wiktionary Polio at Curlie Retrieved from https en wikipedia org w index php title Polio amp oldid 1141547226, wikipedia, wiki, book, books, library,

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