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Poliomyelitis

Poliomyelitis

Definition

Poliomyelitis is an infectious disease that is caused by a subgroup of viruses. The hallmark of the disease is the rapid development of paralysis. Poliomyelitis is also commonly called polio. Once a cause of widespread public health measures to control epidemics, polio is now on the brink of eradication.

Description

The term poliomyelitis comes from the Greek words polio, meaning gray, and myelon, referring to the spinal cord. The term is accurate, as an important consequence of the disease is the involvement of the spinal cord with resulting paralysis.

Poliomyelitis was first described in 1789, although it likely dates back many centuries prior to that time. Outbreaks occurred in Europe and the United States beginning in the early nineteenth century. For the next hundred years, outbreaks became a regular summer and fall event in northern regions. As time passed, the number of cases and people crippled by the infection rose. By 1952, more than 21,000 people in the United States were paralyzed after a bout of poliomyelitis.

The manufacture and widespread use of several vaccines beginning in the 1950s drastically reduced the number of cases of poliomyelitis. In the United States, the last reported case of polio acquired from a wild-type (original form of a naturally occurring) virus was in 1979.

Demographics

Humans are the only known carriers of the polio virus. Poliomyelitis most commonly affects children under the age of five. Several generations ago, the disease was much more common than it is now. Even in the 1950s, poliomyelitis was global in its occurrence. Many children in underdeveloped and developed countries, including the United States, were susceptible. With the successful development of vaccines and the implementation of global vaccination campaigns, the infection has been drastically reduced. As of 2004, only isolated pockets of disease remain. These hot spots include areas in Africa, India, and the eastern Mediterranean.

Males and females are equally susceptible to polio. Irreversible paralysis, usually in the legs, occurs in about one of every 200 polio infections.

Causes and symptoms

Poliomyelitis originates with a viral infection. Poliovirus is a member of a group of viruses designated as enteroviruses. The viruses contain ribonucleic acid (RNA) as their genetic material. More specifically, the various polioviruses belong in a group (or family) called Picornaviridae.

There are three types of poliovirus that are related to each other based on their recognition by the body's immune system. This sort of a relationship is called a serotype. The three poliovirus serotypes are P1, P2, and P3. Even though they are closely related immunologically, developing immunity to one serotype is no guarantee of protection from infection from the other two serotypes. Thus, vaccines are geared towards producing an immune response that will be protective against all three serotypes.

Enteroviruses can be found in the gastrointestinal tract and are not often dissolved by the acidic conditions. Thus, poliovirus can be swallowed and remain intact, capable of causing an infection. As the virus particles lodge at the back of the throat in the pharynx, or are swallowed and end up in the intestinal tract, the viruses can begin to multiply. Like all viruses, the multiplication requires a host cell, in this case, cells lining the throat and intestines.

Shortly after the virus enters a person, viral particles can be recovered from the throat and from feces. About one week later, the virus is not usually detectable in the throat. However, virus can continue to be excreted in the feces for several more weeks. During this time, symptoms of the disease do not develop. Thus, the virus can be unknowingly passed to others via the oral or fecal-to-oral route. This transmission is a common method of transfer of a variety of viral and bacterial infections in settings like daycare centers.

Subsequently, the poliovirus invades lymph tissue. From there, the virus can enter the bloodstream and infect cells of the central nervous system . This typically takes from six to 20 days after infection. Multiplication of the virus inside motor neurons in environments like the brain destroys the host cells and causes paralysis. The appearance of paralysis is rapid.

Up to 95% of polio infections do not produce any symptoms or damage. However, these individuals can still excrete the virus in their feces, and so are capable of infecting others. For every 200 people who escape the effects of poliomyelitis, about one person becomes paralyzed.

Approximately 48% of polio infections are minor, and consist of fairly nonspecific symptoms, including sore throat and fever, nausea, vomiting, abdominal pain , or constipation. Recovery is complete in about a week. Indeed, a person may not know the difference between this brush with polio and the flu. This condition is known as abortive poliomyelitis. There is no involvement of the central nervous system.

In 12% of infections, a condition called nonparalytic aseptic meningitis is produced. Nonspecific symptoms characterize this condition, followed several days later by stiffness in the neck, back, and/or legs. The symptoms last from 210 days. Recovery is complete.

Less than 1% of those who are infected with the poliovirus develop what is termed flaccid paralysis. Paralysis appears anywhere from one to 10 days after symptoms

that include loss of reflexes, severe muscle aches, and muscle spasms in the arms, legs, or back. In children, the initial symptoms can begin to fade before paralysis appears.

Over the next few days, the paralysis becomes worse. For many people, muscle strength eventually returns. However, for those who still have weak muscles and/or paralysis a year later, the changes are likely permanent.

Types of paralytic poliomyelitis

There are three types of paralysis that can develop in poliomyelitis. The first is called spinal polio. This is the most common form of polio-related paralysis, and accounted for nearly 80% of all polio-related paralysis from 1969 to 1979. This type produces the classical image of a person whose legs have been paralyzed. The second type is known as bulbar polio. This type accounts for about 2% of known cases. Stiffness and paralysis typically occurs in the neck and head. The third type of polio-related paralysis is called bulbospinal polio. A combination of the previous two conditions, it accounts for nearly 20% of paralysis.

Postpolio syndrome

In almost half of those who contract polio in childhood, muscle pain and weakness reappears three or four decades later. Postpolio syndrome does not appear to be caused by a recurrence of the viral infection, as no virus can be detected in the feces. Rather, it may result from motor neurons damaged in the initial bout of polio that fail to operate properly decades later. The reason for the failure is not known.

Diagnosis

The diagnosis of poliomyelitis is based on the recovery of the virus from the throat or feces of a person. It is possible to isolate the virus from the cerebrospinal fluid, but this is uncommon. When the virus is recovered, specialized testing can be done to determine if the virus is wild type (that is, it has been acquired from the environment), or whether it is a vaccine type (polio vaccines utilize intact, but weakened viruses).

Another means of diagnosis relies on the detection of antibodies that have been produced by the virus. Since antibodies are produced as a part of the vaccination process, physicians focus on the increasing levels of antibodies over a short time as evidence that the body is battling an active viral infection.

Still another diagnostic test detects increased number of white blood cells and protein in the cerebrospinal fluid. This is a more general response to infections. Other conditions can present similar symptoms, and need to be ruled out when diagnosing poliomyelitis. These include Guillain-Barré syndrome , meningitis, and encephalitis.

Treatment team

The treatment team ideally consists of the family physician, neurologist , infectious disease specialist, physical therapists, occupational therapists, specialty nurses, and family members. In field conditions in developing countries, the treatment team may consist of a physician and direct caregivers only. World health agencies rapidly mobilize to provide care and vaccinations in order to contain isolated outbreaks in developing countries.

Treatment

Prevention is the watchword for poliomyelitis, and prevention consists of vaccination. There are two polio vaccines available; inactivated (Salk) poliovirus vaccine, and oral poliovirus vaccine.

The inactivated vaccine was devised by American physician Jonas Salk (19141995) in the 1950s. The vaccine contains all three serotypes of the poliovirus. The viruses, which are inactivated and incapable of causing an infection, are grown in a type of monkey kidney cell. When injected, the viruses stimulate an immune response that is protective. Initially, vaccine impurity was the cause of illness and death in some people who received the Salk vaccine. Refinement of the vaccine preparation eliminated these unwanted effects. Still, in the 1990s, a controversy arose regarding the vaccine as a suggested source of acquired immunodeficiency syndrome (AIDS ), based on the known presence of the AIDS virus in monkey tissue cells. However, scrupulously conducted examinations ruled out this suggestion.

The oral vaccine was developed by Polish-born American physician Albert Sabin (19061993) in the late 1950s and was licensed for use in 1963. This vaccine has largely replaced the injected Salk vaccine. The vaccine also contains live, but weakened (attenuated) poliovirus.

A series of vaccinations given at two, four, six to 18 months, and four to six years produces a lifelong immunity to the three poliovirus serotypes. In regions where poliomyelitis is actively occurring, even a single dose of vaccine can provide adequate protection from infection during the outbreak.

In 2002, a new formulation of polio vaccine was approved for use in the United States. In addition to the polioviruses, the vaccine also bestows immunity to the virus that causes hepatitis B.

Recovery and rehabilitation

There is no cure for poliomyelitis. Some people can partially recover from paralysis, while the condition is irreversible in others. Physical and occupational therapies can be helpful in providing strengthening exercises and assistive devices for walking, but these are seldom available in remote areas of developing countries where polio outbreaks still occur.

Prognosis

Among those who are paralyzed by the viral infection, 510% overall die due to the paralysis of muscles used for breathing. For every 100 people who become paralyzed by the viral infection, two to five children and 1530% of adults will die from polio.

Special concerns

Vaccination can produce reactions ranging from a transient and minor skin irritation and allergic reaction to some components of the oral vaccine to paralysis. The latter, termed vaccine-associated paralytic polio, is very rare. The condition is associated more with the injectable vaccine than with the vaccine given orally. Nonetheless, adults can be affected. From 19801998, 152 adults in the United States developed some degree of paralysis from polio vaccination.

The decision by Nigeria to suspend its vaccination program in 2001 contributed to a rise in the number of polio cases in the African country. Nigeria has since reinstated the vaccination program. The Nigerian experience points out that continued vigilance is necessary to keep poliomyelitis under control.

Since the widespread availability of vaccines, the number of cases of poliomyelitis worldwide has decreased by over 99% since 1988. That year, the estimated number of cases was more than 350,000. As of April 2003, the number of cases was reduced to 1,919. The dramatic reduction in the disease is attributed to a multinational worldwide vaccination effort that began in 1988. The program was spearheaded by organizations such as the World Health Organization.

The effort intensified during the first half of 2004, with the urgent distribution of polio vaccine to 250 million children in the world's remaining hotspots. As of April 2004, the number of polio cases worldwide caused by a wild-type virus was reduced to 89. World health officials aim to interrupt the transmission of all wild-type polio virus by the year 2005.

Resources

BOOKS

Bruno, Richard L. The Polio Paradox: Understanding and Treating "Post-Polio Syndrome" and Chronic Fatigue. New York: Warner Books, 2003.

Oshinsky, David, Polio: An American Story. New York: Oxford University Press, 2004.

Salgado, Sebastio, and Kofi Annan. The End of Polio: A Global Effort to End a Disease. Boston: Bulfinch, 2003.

PERIODICALS

Centers for Disease Control and Prevention. "Progress toward global eradication of poliomyelitis." Morbidity and Mortality Weekly Report (July 2003): 366369.

OTHER

Dowdle, Walter, et al. "Preventing Polio from Becoming a Reemerging Disease." Panel Summary from the 2000 Emerging Infectious Diseases Conference in Atlanta, Georgia. CDC. April 23, 2004 (June 2, 2004). <http://www.cdc.gov/ncidod/eid/vol7no3_supp/dowdle.htm>.

World Health Organization. "Poliomyelitis." April 14, 2004 (June 2, 2004). <http://www.who.int/mediacentre/factsheets/fs114/en/>.

ORGANIZATIONS

World Health Organization. Avenue Appia 20, Geneva, Switzerland. + 41 22 791 2111; Fax: + 41 22 791 3111. info@who.int. <http://www.who.int>.

Brian Douglas Hoyle, PhD

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Poliomyelitis

POLIOMYELITIS

POLIOMYELITIS, or infantile paralysis, was one of the most feared diseases of the twentieth century, especially for its ability to cripple children and adolescents. The disease is caused by one of three strains of intestinal virus that under certain conditions invades and damages or destroys the anterior horn cells of the spinal cord. Paralysis is caused when damaged or destroyed nerves can no longer enervate muscles. The virus is commonly spread through contaminated fecal material. Before modern sanitation the poliovirus was constantly present, and most individuals were infected as young children, thereby gaining protective antibodies. Epidemics occurred when modern sanitation interrupted virus circulation for several years, creating a large susceptible population. In epidemics, perhaps as many as 90 to 95 percent of those infected had inapparent cases and a flu-like illness with no paralysis. Four to eight percent of those infected had an abortive case with mild symptoms. Less than 2 percent of all infections reached the central nervous system and caused paralysis. Polio killed when the muscles involved in breathing were paralyzed, but the disease was rarely fatal.

The first sizable polio epidemic in the United States occurred in Vermont in 1894. Recurrent epidemics in Europe and North America sparked research on the disease, and in 1908 the Vienna immunologist Karl Landsteiner discovered the poliovirus. Simon Flexner, the director of the Rockefeller Institute for Medical Research in New York, soon isolated the virus in the United States and discovered polio antibodies in patients.

In 1916, New York and the Northeast experienced the nation's most severe polio epidemic, with 27,000 cases and 6,000 deaths. In New York City alone there were 8,928 cases and 2,407 deaths. This epidemic puzzled physicians and frightened citizens. Polio struck both infants and adults, individuals living in clean, sanitary conditions and those living in filth, the wealthy and the poor. Lacking effective cures and vaccines, public health officials conducted a campaign to clean up the city and eradicate the flies believed to carry the disease. Polio patients were quarantined in their homes or removed, sometimes forcibly, to hastily established isolation hospitals. For the next four decades epidemics of poliomyelitis struck some part of the nation every year.

In 1921, Franklin D. Roosevelt, who later served as governor of New York and president of the United States, developed polio while vacationing at the family home. Seeking to regain the use of his paralyzed legs, he discovered the therapeutic effects of warm mineral water at a failing resort in Warm Springs, Georgia. In 1926 he purchased the resort and, with the help of his law partner, Basil O'Connor, turned it into a model facility for polio rehabilitation, although Roosevelt himself never walked unaided.

During the 1920s and 1930s, scientists and physicians sought to better understand the disease and to find a cure or vaccine. The researchers James D. Trask, John R. Paul, and Dorothy Horstmann of the Yale University Poliomyelitis Study Unit confirmed polio's character as an intestinal disease when they isolated the virus in water supplies and sewage during epidemics. Australian scientists in 1931 discovered that there were at least two different strains of poliovirus. Scientists ultimately discovered a third strain and placed the poliovirus in the family of enteroviruses. In 1935 two American physicians, Maurice Brodie in New York and John A. Kolmer in Philadelphia, developed and tested polio vaccines. These vaccines, however, proved ineffective and may actually have caused cases of the disease.

Polio rehabilitation also advanced in the 1930s, especially at the Georgia Warm Springs Foundation established by Roosevelt. The President's Birthday Ball Commission began raising funds in 1934 to support rehabilitation and research and was succeeded in 1938 by the National Foundation for Infantile Paralysis headed by Basil O'Connor. The National Foundation's March of Dimes campaign raised over $600 million between 1938 and 1962. About 60 percent of this money assisted individuals with hospital and doctor bills, and about 11 percent was spent on grants to scientists. The iron lung, a large canister-shaped respirator that "breathed" for patients with paralyzed respiratory muscles was developed in the 1930s. In the 1940s, Elizabeth Kenny, an Australian nurse, introduced her unorthodox ideas for treating polio paralysis. In place of immobility and casts to prevent the contraction of paralyzed limbs, Kenny applied hot packs to sooth paralyzed muscles and movement in order to maintain flexibility and retrain paralyzed muscles. Although many doctors rejected her theories about the causes of polio paralysis, her therapeutic practices soon became commonplace.

In the late 1940s, John F. Enders, Thomas H. Weller, and Frederick C. Robbins, physicians at Harvard funded by the National Foundation, first grew poliovirus on tissue culture outside the body, necessary for a successful vaccine. They won the Nobel Prize in 1954 for their discovery. The National Foundation also funded a typing program to identify all the possible strains of the virus in anticipation of producing a vaccine against every variant.

This research occurred against the background of an increasing incidence of epidemics in the late 1940s and early 1950s. Nine of the ten worst years for polio occurred between 1945 and 1955, and the epidemic of 1952 was second only to 1916 in its severity. The improved sanitation of the postwar years, the move to the suburbs, and the baby boom ensured that many children and even adolescents were vulnerable. Those years were marked by summers of fear when parents kept their children out of swimming pools and movie theaters and warned them against drinking from water fountains. The fund-raising of the March of Dimes, the information disseminated by the National Foundation, and the heartbreaking personal narratives that appeared in popular magazines kept polio in the forefront of the nation's consciousness. The specter of the crippling paralysis of polio threatened the postwar American Dream of healthy, happy children.


The fund-raising efforts of the March of Dimes and the laboratory work of the physicians came together in the 1950s. Jonas Salk, a University of Pittsburgh physician, applied lessons he had learned working on influenza vaccine and developed a successful killed virus vaccine that could be mass produced. By the early 1950s he was conducting preliminary trials of the vaccine. In 1954 the National Foundation arranged for a large-scale field trial of the Salk vaccine conducted by Dr. Thomas Francis Jr. of the University of Michigan. Over 1.8 million children were enrolled as "polio pioneers" in the trial. On 12 April 1955, Francis announced that the Salk vaccine was both safe and effective in protecting vaccinated children from polio. The U.S. government licensed the vaccine the same day. Basil O'Connor had already ordered millions of doses from pharmaceutical companies in order to begin a mass vaccination immediately. Unfortunately, a few weeks later, a bad batch of vaccine produced by Cutter Laboratories resulted in more than 200 cases of vaccine-associated poliomyelitis, including eleven deaths. This was an isolated episode, and the vaccination of America's children soon continued. Even as many children were protected by the Salk vaccine, Albert Sabin, also supported by the National Foundation, worked on an attenuated poliovirus vaccine. An attenuated vaccine, in which the virus was live but significantly weakened, had several advantages. It induced a stronger, longer lasting immune response; immunity was achieved more quickly; and it could be given orally instead of being injected. After field trials in the United States, the Soviet Union, and elsewhere, the Sabin vaccine was licensed for use in 1962. These two vaccines virtually eliminated poliomyelitis in the United States by the early 1960s. Since then only a handful of cases have occurred annually, usually in new immigrants or as vaccine-associated cases.

The survivors of the postwar polio epidemics often spent long periods in rehabilitation hospitals before being fitted with braces, wheelchairs, and respirators that allowed them to return to families, school, and work. Because of the barriers they faced in attempting to live and work, polio survivors were often in the forefront of the disability rights movement that emerged in the 1970s. Activists like Ed Roberts, who was one of the founders of the Independent Living Movement, insisted that individuals with disabilities had a right to accessible living and working environments. In the 1980s, many polio survivors began experiencing increased pain, muscle weakness and even paralysis that physicians eventually identified as post-polio syndrome, an apparent effect of the overuse of nerves and muscles to compensate for the destruction caused by the initial infection. The oral polio vaccine also came under attack in the United States for causing eight to ten cases of polio every year. In 2000 the federal government recommended returning to a safer Salk-type killed virus. The Sabin vaccine, however, remained in use overseas as the World Health Organization tried to eradicate the poliovirus worldwide. Thus in the twenty-first century, poliomyelitis, which was so feared in the twentieth century, may become only the second infectious disease, after smallpox, to be eliminated as a threat to humans.

BIBLIOGRAPHY

Black, Kathryn. In the Shadow of Polio: A Personal and Social History. Reading, Mass.: Addison-Wesley, 1996.

Gould, Tony. A Summer Plague: Polio and Its Survivors. New Haven: Yale University Press, 1995.

Paul, John R. A History of Poliomyelitis. New Haven: Yale University Press, 1971.

Rogers, Naomi. Dirt and Disease: Polio Before FDR. New Brunswick: Rutgers University Press, 1990.

Seavey, Nina Gilden, Jane S. Smith, and Paul Wagner. A Paralyzing Fear: The Triumph Over Polio in America. New York: TV Books, 1998.

Smith, Jane S. Patenting the Sun: Polio and the Salk Vaccine. New York: William Morrow, 1990.

Daniel J.Wilson

See alsoEpidemics and Public Health ; March of Dimes ; Medical Research .

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Poliomyelitis

Poliomyelitis

Poliomyelitis, or polio, is a serious infectious disease that attacks muscle-controlling nerves and can eventually cause paralysis. Poliomyelitis, sometimes called infantile paralysis, is caused by one of three related viruses, and it primarily affects children. However, adults can also be infected. There is no drug that can cure the disease once a person has been infected.

Poliomyelitis is infectious, meaning it is spread primarily through contact with someone who already has the disease. The virus enters the body through the mouth and then enters the bloodstream. Once in the central nervous system, it travels along nerve pathways. In severe cases, it reaches the spinal cord or the brain where it causes lesions (abnormal changes in the structure of body tissue).

Symptoms usually begin to show one to three weeks after the virus is contracted. In some cases, the attack may be so mild that it goes unnoticed. The body quickly develops immunity and the virus is eliminated. A more severe attack gives rise to symptoms that resemble those of influenza (fever, sore throat, vomiting, diarrhea, stiff neck and back, and muscle pain). About two-thirds of people infected in such a way recover without suffering any paralysis.

A serious attack occurs if the virus reaches the central nervous system. Muscle tissue weakens and paralysis develops. Usually the paralysis is only temporary, and about 50 percent of people infected recover without permanent disability. However, if any of the cells attacked by the virus are destroyed, they cannot be replaced and muscle function is permanently impaired. About 25 percent of people who recover after being seriously infected have severe permanent disability.

Words to Know

Epidemic: Rapidly spreading outbreak of a contagious disease.

Iron lung: Device developed in 1928 by Philip Drinker to maintain artificial respiration in a person over a long period of time.

Sabin vaccine: Oral polio vaccine developed by Albert Sabin from weakened live polio viruses and introduced in 1961.

Salk vaccine: Polio vaccine developed by Jonas Salk in the mid-1950s from dead polio viruses and given through injection.

If the nerve cells of the brain are attacked (a condition known as bulbar poliomyelitis), the muscles controlling swallowing, heartbeat, and breathing are paralyzed. The result is death.

Development of the iron lung

Incidents of poliomyelitis can be traced back to ancient Egypt. The first recorded poliomyelitis epidemic (a rapidly spreading outbreak of a contagious disease) was in Sweden in 1881. From that time until the mid-1900s, there were regular epidemics throughout the world.

To help those people infected with poliomyelitis whose respiratory (breathing) muscles had been paralyzed, American physiologist Philip Drinker (18931977) invented the Drinker tank respirator (commonly known as the iron lung) in 1928. It is a device to maintain artificial respiration in a person over a long period of time. The iron lung is an airtight cylindrical steel drum that encloses the entire body, with only a patient's head exposed. Pumps connected to the device lower and raise air pressure within the drum, which contracts and expands a patient's chest walls (imitating the action of breathing). Many poliomyelitis patients were kept alive in such a manner, but it was not a cure for the disease.

Salk and Sabin vaccines

In the early 1950s, American microbiologist Jonas Salk (19141995) developed the first vaccine to prevent the spread of the disease. The Salk vaccine is composed of killed poliomyelitis virus. A series of three of

four injections with the killed-virus vaccine prompts the body's immune system to produce antibodies that will attack any future invading forms of the disease. In 1955, the vaccine was officially pronounced effective, potent, and safe in almost 90 percent of cases. The major defense the Salk vaccine provides against polio viruses is to prevent them from spreading from the digestive system to the nervous and respiratory systems. But it cannot prevent the viruses from entering the intestinal tract.

In the late 1950s, Russian-born American virologist Albert Sabin (19061993) developed a vaccine that has proven to provide longer immunity against the disease than the Salk vaccine. The Sabin vaccine is composed of live (but weakened and harmless) poliomyelitis virus. After four years of worldwide tests, the vaccine became available to the public in 1961. The advantage of the Sabin vaccine is that it is given orally and offers protection with only a single dose. The vaccine goes straight to the intestinal tract and builds up immunity there as well as in other parts of the body.

Both vaccines are effective against all forms of the poliomyelitis virus. Near the end of the twentieth century, health organizations reported that poliomyelitis was close to extinction in the Western Hemisphere.

[See also Vaccine ]

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Poliomyelitis

POLIOMYELITIS

Poliomyelitis, or infantile paralysis, is a highly infectious disease caused by three serotypes of polioviruses. These viruses belong to the Enterovirsus genus of the family Picornaviridae. The infection is transmitted from person to person and rarely produces clinical symptoms. Less than 1 percent of infections will result in paralysis. Death may result, however, especially if respiratory muscles are affected.

Although archeological findings suggest that paralytic poliomyelitis existed before the modern era, the importance of the disease was not recognized until the late nineteenth century. Annual outbreaks of poliomyelitis involving thousands of cases occurred during summer and early fall in various areas of the northern hemisphere during the first half of the twentieth century, making poliomyelitis the leading cause of permanent disability and the cause of numerous premature deaths. The Drinker respirator, also known as the "iron lung," allowed a rapid reduction of poliomyelitis mortality in the 1930s and 1940s.

A major breakthrough in poliomyelitis control took place in 1949, when John F. Enders, Frederick C. Robbins, and Thomas H. Weller developed a tissue culture system for polioviruses. The availability of cultured viruses opened the way to vaccine development. The first poliovirus vaccines were licensed for use in the United States in 1955. These vaccines, developed by Jonas Salk, consisted of formalin-inactivated viruses administered through injections. In 1963, a live oral vaccine, developed by Albert Sabin, was licensed. Within ten years of the introduction of vaccines, the number of poliomyelitis cases decreased by over 95 percent in the United States, and the last case induced by indigenous transmission of wild poliovirus in the United States was detected in 1979. Poliovirus vaccines also allowed rapid declines in disease incidence in Canada, most European countries, Australia, and New Zealand. In Cuba, a two-round mass vaccination campaign in 1962 interrupted poliovirus transmission and rendered the island free of polio.

Most developing countries did not benefit from effective poliomyelitis control before the development of national control programs in the late 1970s. Mass vaccination campaigns, introduced in the Americas during the early 1980s, proved to be an effective means of bringing poliomyelitis under control. The last case of poliomyelitis in the Americas was detected in Peru in 1991, and the western hemisphere was certified as poliofree in 1994.

In 1988, the World Health Assembly launched the Poliomyelitis Eradication Initiative, with a goal of terminating the circulation of wild polioviruses by the year 2000. This worldwide effort relies on three main strategies: high levels of vaccination through routine programs; supplementary vaccination in the form of national immunization days

and local door-to-door immunization ("moppingup") campaigns; and surveillance and investigation of all cases that resemble acute poliomyelitis (acute flaccid paralysis). From 1988 to 1999, the global number of estimated poliomyelitis cases decreased from 350,000 to 20,000.

An important benefit of achieving the Poliomyelitis Eradication Initiative goal will be the discontinuation of poliovirus vaccination. Stopping vaccination will require certifying all areas of the world to be free of wild poliovirus. It will also be necessary to ensure that all infectious and potentially infectious material are contained in maximum safety facilities and to stockpile enough vaccines to respond to any outbreak that might occur should poliovirus be released intentionally or unintentionally. In this way poliomyelitis eradication would follow the path pioneered by smallpox eradication.

Patrick L. F. Zuber

(see also: Communicable Disease Control; Immunizations; Smallpox )

Bibliography

Centers for Disease Control and Prevention (2000). "Poliomyelitis Prevention in the United States: Updated Recommendations of the Advisory Committee on Immunization Practices (AICP)." Morbidity and Mortality Weekly Report 49(RR-5):122.

Robbins, F. C. (1999). "The History of Polio Vaccine Development." In Vaccine, 3rd edition, eds. S. A. Plotkin and W. A. Orenstein. Philadelphia: W. B. Saunders.

Sutter, R. W; Cochi, S. L; and Melnick, J. L. (1999). "Live Attenuated Poliovirus Vaccines." In Vaccine, 3rd edition, eds. S. A. Plotkin and W. A. Orenstein. Philadelphia: W. B. Saunders.

World Health Organization. Polio Eradication. Available at http://www.polioeradication.org.

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poliomyelitis

poliomyelitis (pō´lēōmī´əlī´tĬs), polio, or infantile paralysis, acute viral infection, mainly of children but also affecting older persons. There are three immunologic types of poliomyelitis virus; exposure to one type produces immunity only to that type, so infection with the other types is still possible. Spread of the infection is primarily through contact with an infected person. Most people who contract polio either exhibit no symptoms or experience only minor illness; however, such individuals can harbor the virus and spread it to others. Less than 1% of the people who get infected develop paralysis.

The virus enters the body by way of the mouth, invades the bloodstream, and may be carried to the central nervous system, where it causes lesions of the gray matter of the spinal cord and brain. The illness begins with fever, headache, stiff neck and back, and muscle pain and tenderness. If there is involvement of the central nervous system, paralysis ensues. Of those patients who develop paralytic poliomyelitis, about 25% sustain severe permanent disability, another 25% have mild disabilities, and 50% recover with no residual paralysis. The disease is usually fatal if the nerve cells in the brain are attacked (bulbar poliomyelitis), causing paralysis of essential muscles, such as those controlling swallowing, heartbeat, and respiration. There is no specific drug for treatment. For reasons not clearly understood, some people who have had severe polio experience postpolio syndrome, a condition in which new weakness and pain occurs years later in previously affected muscles.

The incidence of poliomyelitis declined radically in the United States when a mass immunization program with the Salk vaccine, a preparation made from killed organisms and injected, was begun in 1955. A live-virus vaccine had earlier been developed (1948) by Hilary Koprowski, but it was never approved for use in the United States. By 1961 the Sabin vaccine, a preparation made from weakened living organisms and taken orally, was released for use. Since then the disease has been virtually eliminated in the Americas, Europe, and Australasia, but vaccination programs continue because of polio's existence in other parts of the world (mainly areas of South Asia and West Africa) and the ease of travel.

In 1988 the World Health Organization began a global vaccination campaign to eradicate the disease—which continued to paralyze hundreds of thousands of children each year—by 2000. Although the date of eradication was later pushed back to 2005 (and even later a set deadline was abandoned), there were by 2003 less than a thousand new cases of polio worldwide, and the last last known case of type 2 poliomyelitis occurred in 1999. In 2003–4, however, the campaign was slowed when Muslim states in N Nigeria refused to use vaccines they believed would sterilize women, leading to an increase in cases there and in neighboring countries and to outbreaks of the disease in 17 countries including Yemen and Indonesia. Since then there have been other significant new outbreaks, from various sources, in some African nations and in Central Asia; the civil war in Syria resulted an outbreak there by 2013. Nonetheless, according to WHO, polio remained endemic only in Pakistan, Afghanistan, and Nigeria in 2014.

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poliomyelitis

poliomyelitis (infantile paralysis, polio) (poh-li-oh-my-ĕ-ly-tis) n. an infectious virus disease affecting the central nervous system. Immunization, using the Sabin vaccine or the Salk vaccine, is highly effective. abortive p. poliomyelitis in which only the throat and intestines are infected and the symptoms are those of a stomach upset or influenza. bulbar p. paralytic poliomyelitis in which the muscles of the respiratory system are affected. nonparalytic p. a form of the disease in which the symptoms of abortive poliomyelitis are accompanied by muscle stiffness. paralytic p. a less common form of polio in which the symptoms of the milder forms of the disease are followed by weakness and eventual paralysis of the muscles. See also post-polio syndrome.

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poliomyelitis

poliomyelitis (polio) Acute viral infection of the nervous system affecting the nerves that activate muscles. Often a mild disease with effects limited to the throat and intestine, it is nonetheless potentially serious, with paralysis occurring in 1% of patients. It becomes life-threatening only if the breathing muscles are affected, in which case the person may need artificial ventilation. It has become rare in developed countries since the introduction of vaccination in the mid-1950s.

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poliomyelitis

po·li·o·my·e·li·tis / ˌpōlēōˌmīəˈlītis/ • n. Med. an infectious viral disease that affects the central nervous system and can cause temporary or permanent paralysis.

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"poliomyelitis." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 17 Aug. 2017 <http://www.encyclopedia.com>.

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poliomyelitis

poliomyelitis (path.) inflammation of the grey matter of the spinal cord. XIX. f. Gr. poliós grey + muelós marrow; see -ITIS. abbr. polio XX.

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