Poliomyelitis

Incubation and natural immunity

The iron lung

World eradication of polio

Feasibility for eradication

Polio vaccines

Need for surveillance

Importance of laboratories

Cost of global eradication

Treatment of post-polio syndrome

Use of drugs

Resources

There are three viruses responsible for the infectious disease known as poliomyelitis. Previously known as infantile paralysis, the disease is commonly referred to as polio. While polio usually afflicts young children, adults can also contract the disease.

Infection from poliomyelitis is spread through contact with someone who already has the disease or as a result of poor sanitation where human waste products infect others. The mouth is the usual pathway of the virus which then enters the blood system. Paralysis mostly to the arms and legs occurs from lesions to the central nervous system. These lesions occur when the polio viruses begin to invade the central nervous system.

Clinical reactions to the polio viruses can range from none to mild symptoms resembling the common cold (headache, sore throat, slight fever). These symptoms can vanish in a short period of time, anywhere from one to three days. A major illness of polio can be defined when the viruses attack the central nervous system, and even in these cases about 50% of the patients will fully recover. Of the remaining 50% about half of those will retain some limited disabling after-effects, while the other one-half will show signs of permanent disability.

Because infants in underdeveloped parts of the world may have built up immunity from their mothers who had been exposed to the virus, there has been a belief that these children were less at risk of contracting polio than children in advanced countries with improved sanitation. Demographic statistics of incident rates, however, tend to raise questions about the effectiveness of natural, infant immunities developing in backward countries. Immunization programs against poliomyelitis as well as other common childhood diseases is still carried on by the World Health Organization and its partners as the only reliable way of eradicating the disease.

In the 1950s, two types of polio vaccines were developed in the United States. One type, the Salk vaccine, named after its developer Jonas Salk, used dead polio viruses that were injected. The other type is called the Sabin vaccine, after Albert Sabin, and is an oral vaccine using a weaker strain of the polio viruses for immunity.

Since both vaccines are effective against all three strains of the polio viruses, there has been a virtual eradication of the disease in the United States and other countries that are able to employ a successful immunization program for their populations.

For those who contracted the disease before the vaccination programs became fully effective, there have been reports of a disorder which is referred to as post-polio syndrome. This condition is characterized by fatigue, pains in the joints and muscles, problems with breathing, and a loss of muscle strength. Physical and occupational treatment therapies help deal with this problem.

Incubation and natural immunity

The term infantile paralysis for poliomyelitis was appropriate to the extent that the majority of cases, 70-90%, do occur in early childhood, below the age of three. In countries with temperate climates, the infection rate rises seasonally during the heat and humidity of the summer months. The viruses are passed along either orally or through contact with infected feces or even through inhalation of infected moisture droplets, such as by a sneeze or cough.

Incubation for the virus runs from four to 35 days. Symptoms in most cases will begin to show after one to three weeks after contracting the virus.

The view is still current with some epidemiologists (scientists who track and study ways of preventing the spread of disease) that by the age of six, children in countries with poor sanitation have often acquired a permanent immunity to polio, whereas children in countries with good sanitation are more apt to get the disease in their adult years since they were not exposed to it at an earlier period of life. Statistical analysis has left this assumption open to debate.

The iron lung

The iron lung was developed for cases of polio that paralyzed the muscles necessary for breathing. The iron lung is an early artificial respirator. The patient’s body is enclosed in a metal tank that uses air pressure changes to expand and contract the chest walls. In the 1920s, a physiologist named Philip Drinker invented this innovative way of dealing with the respiratory problems of polio patients. The iron lung used a continuous power source which made it superior to existing respirators.

Drinker’s original design was improved by physicians to increase the patient’s care and comfort. The medical community depended on the iron lung in the treatment of patients with paralysis of the respiratory muscles. It was heavily used during the polio epidemic of 1931. Large, hospital-based respirator centers were developed to care for the many polio patients with respiratory paralysis. These centers were the predecessors of today’s intensive care units.

World eradication of polio

The goal for the total eradication of polio, just as small pox has been eliminated, has annually been nearing a reality. About 600,000 cases of polio were reported each year before the introduction and full use of the polio vaccines. That number held firm from the mid-1950s to the early part of the next decade of the 1960s. By 1992, the number of reported cases throughout the world dropped to 15,406. Peru in 1991 was the only country in the western hemisphere to report one case of polio. Since 2001, fewer than two thousand cases of polio have been reported worldwide each year.

It was the World Health Organization that was responsible for the world eradication of smallpox by waging an 11-year campaign against the virus that caused it, the variola virus. WHO was able to bring countries together to use a vaccine that had been discovered 170 years ago. The polio viruses, however, are still active and there really may be 10 times as much polio in the world than is actually officially reported.

Feasibility for eradication

One of the problems of testing for the eradication of polio infections is that many persons infected with polio do not show any clinical symptoms. They are asymptomatic. Fewer than 1% of polio infections lead to paralysis and most of the cases that go on to paralysis are caused by the type 1 poliovirus. Type 1 is also the virus responsible for most polio outbreaks.

Another problem in tracking the polio virus is that there are other viruses (Enteroviruses) that create symptoms that are similar to the ones created by the polio viruses. There are also some unusual types of symptoms in some polio infections that resemble a disorder known as Guillain-Barre syndrome. Only a careful laboratory examination that includes isolating the viruses from the patient’s stool can be considered for giving a correct diagnosis of the infection. The presence of such laboratory facilities, especially in developing areas, therefore, becomes an important factor in the program to eliminate infections from polio viruses.

Polio vaccines

In 1955, the Salk inactivated polio vaccine was introduced. It was followed by the Sabin live, attenuated oral vaccine in 1961. These two vaccines have made it possible to attempt to eliminate polio on a global level.

The Salk vaccine as it has been presently developed produces a high level of immunity after two or three injections with only minor side-effects. The major defense the Salk vaccine provides against polio viruses is to prevent them from spreading from the digestive system to the nervous system and respiratory system. But it cannot prevent the viruses from entering the intestinaltract. TheSalkvaccinehas been effective in certain countries, like those in Scandinavia and the Netherlands, where children received a minimum of six polio immunizations before reaching the age of 15. Those countries have good sanitation and the major form of spreading the viruses was through respiratory contagion.

In countries that do not have good sanitation, the Sabin vaccine is preferred because as an oral vaccination, it is goes straight to the intestinal tract and builds up immunity there as well as in other parts of the body. There is, however, the rare adverse side-effect of 1 out of 2,500,000 doses of the Sabin vaccine producing a case of poliomyelitis.

The number of doses necessary in order to achieve a high level of immunity for the Sabin oral vaccine in temperate, economically advanced countries may be two or three. In tropical countries the degree of immunization is not as high against all three types of polio viruses. The effectiveness of the Sabin oral vaccine in tropical countries is improved when it is administered in the cool and dry seasons and when it is given as part of mass campaign where there is a chance of vaccinated persons passing the vaccine virus on to nonvaccinated persons.

Toward the global eradication of polio, the World Health Organization recommends the Sabin oral vaccine for its better performance in creating overall polio immunity, its convenient form of administration, and for its lower cost.

Need for surveillance

For the total eradication of a disease, it is necessary to have the mechanisms for determining the existence of even one solitary instance or case of the disease. That means there must be a quick system of reporting and collection of any suspected occurrence of the disease so that laboratory analysis may be made as soon as possible. Health care providers are given the criteria for determining the presence of the disease. In the case of polio, the appearance of a certain type of paralysis called acute flaccid paralysis along with the Guillain-Barre syndrome for a child under five or any physician diagnosed case of polio at any age should receive immediate attention.

Within 24-48 hours, two stool specimens are collected along with clinical information, other laboratory findings, and information on whether the person has recently traveled. A 60 day follow-up after the onset of the illness should be made to see if there are any paralytic after effects.

Importance of laboratories

Laboratory confirmation of polio viruses requires an efficient network of laboratories. Each WHO region develops a network of laboratories to support the various countries within that area. In these laboratories the staff is trained to isolate and identify the different types of polio viruses. Some countries send specimens to a regional laboratory in a neighboring country. Regional reference laboratories have been set up to tell the differences between vaccine poliovirus from wild poliovirus. A few of these laboratories produce the needed testing agents, do research, and develop training materials for health workers. These

KEY TERMS

Acute flaccid paralysis— An early symptom of poliomyelitis, characterized by weakening or loss of muscle tone.

Guillain-Barre syndrome— A rare disorder of the peripheral nerves that causes weakness and paralysis, usually caused by an allergic reaction to a viral infection.

Iron lung— An artificial respirator developed in the twenties and widely used throughout the polio epidemics in the United States and other countries of the thirties and thereafter.

L-Carnitine— A health food substance being used by some postpolio people.

Post-polio syndrome— A group of symptoms experienced by survivors of the polio epidemics before the period of vaccination.

Sabin vaccine— The oral polio vaccine developed by Albert Sabin from weakened live polio viruses and introduced in 1961; the vaccine WHO recommends for immunization programs.

Salk vaccine— The polio vaccine introduced by Jonas Salk in the mid–1950s using dead polio viruses by injection.

Smallpox— A viral disease with a long history which in 1980 WHO announced was eradicated as a result of an effective worldwide immunization program.

Wild polio virus— As opposed to vaccine polio viruses, which are transmitted as a result of the Sabin vaccine, wild polio viruses are those naturally circulated from natural sources of contagion.

World Health Organization— A body of the United Nations formed in 1948 to manage world health problems, such as epidemics.

laboratories are coordinated with central libraries that contain genotypic information and samples to help in the identification process.

Cost of global eradication

In many of the countries where polio viruses still exist and are transmitted, the cost of eradication cannot be afforded. WHO estimates that global polio eradication, with a 10-year effort, may cost more than a billion dollars. It is argued that countries in the West and those with advancing economies that are free of polio will benefit by the global eradication of polio-myelitis. For example, the United States could save more than $105 million a year on polio vaccine. The Netherlands suffered an outbreak of polio in 1991-92. It spent more than $10 million controlling this outbreak. More money will also have to be spent for the long-term care and rehabilitation for the survivors of the Netherlands’ outbreak. According to the cost-analysis of leading polio epidemiologists, the total cost of eradication could be recovered in savings within a few years of certification that the world is polio-free.

Treatment of post-polio syndrome

For older survivors of previous polio epidemics in the United States and elsewhere there have been a group of related symptoms known as post-polio syndrome.

The amount of exercise recommended for post-polio people has been an issue in question. While it was felt that this syndrome, characterized by muscle atrophy and fatigue, called for some restrictions on exercise because of the weakened condition of the muscles, a more recent view is calling for a reexamination of that position. The newer view is that low-intensity, interval exercise training of muscles is more important than avoidance of exercise even though it becomes more difficult in the aging process. It is important to maintain a high level of activity as well as the right kind and amount of activity. Studies have shown that post-polio muscles that have lost strength can recover strength with targeted exercise.

It is also possible for people with post-polio syndrome to improve their endurance, but it is important for them not to have expectations that exceed their physical limitations. One criterion that can be followed for improving the strength of a limb is to determine how much function remains in the limb. The strength of the limb should at least remain the same with the exercise, but if it begins to decrease, then it is possible it is being overexerted. Experts in the field of physical rehabilitation maintain that the limb should have at least 15% of normal function before it can be further improved with exercise. If it is below that amount the exercise may not help to improve strength and endurance.

Use of drugs

Drug studies show that using high doses of prednisone, a drug used as an immunosuppressant did not produce added strength or endurance. Amantadine, used for Parkinson disease and the fatigue of multiple sclerosis, also was not effective. Another drug, Mestinon, however, showed in one study that people with post-polio could benefit from its use. Another study was less conclusive. Some physicians advise their patients to try it for a one month period starting with a small dose and then over a period of a month to build up the dosage. After the full dosage is reached the user should be able to determine whether or not it will help improve symptoms, especially in the area of strengthening weak muscles. It is particularly recommended to deal with fatigue in emergency situations, such as when driving a car when a low dose can carry the person through the activity safely. Nerve-growth stimulators are being tested for possible effectiveness in reversing muscle atrophy and increasing muscle strength.

Resources

BOOKS

Cefrey, Holly, et al. Epidemics: Deadly Diseases Throughout History (The Plague, AIDS, Tuberculosis, Cholera, Small Pox, Polio, Influenza, and Malaria). New York: Rosen Publishing Group, 2001.

PERIODICALS

Geier, R. “The State of Polio Vaccination In The World.” Toxicology Methods 12 no. 3 (2002): 221-228.

Nair, V. Mohanan. “Polio Eradication - Global Initiative” Journal of Public Health Medicine 24, no. 3 (2002): 207-210.

Ortolon, Ken. “Short On Shots.” Texas Medicine 98, no. 5 (2002): 30-33.

Schanke. “Mild Versus Severe Fatigue In Polio Survivors.” Journal of Rehabilitation Medicine 34, no. 3 (2002): 134-140.

OTHER

“Remembering Polio.” University of Pittsburgh. ψ <http://www.polio.pitt.edu/> (accessed November 26, 2006).

Jordan P. Richman

Poliomyelitis

There are three viruses responsible for the infectious disease now called poliomyelitis. It has been called infantile paralysis and is now commonly referred to as polio. While the disease usually afflicts young children, adults can succumb to it also.

A notable example of polio in an adult was the case of President Franklin Delano Roosevelt, the thirty-second president of the United States. He contracted poliomyelitis at the age of 40. While he was able to return to health through an intense effort of physical therapy , he lost the use of his legs. As the President of the United States he used canes and orthotic devices to stand when he appeared before audiences in the 1930s and 40s. Although he was bound to a wheelchair, to most people he was able to convey the illusion that he was still able to walk.

Infection from poliomyelitis is spread through infectious contact with someone who already has the disease or as a result of poor sanitation where human waste products infect others. The mouth is the usual pathway of the virus which then enters the blood system. Paralysis mostly to the arms and legs occurs from lesions to the central nervous system . These lesions occur when the polio viruses begin to invade the central nervous system.

Clinical reactions to the polio viruses can range from none to symptoms that are mild ones which resemble the common cold (headache, sore throat, slight fever). These symptoms can vanish in a short period of time , anywhere from one to three days. A major illness of polio can be defined when the viruses attack the central nervous system, and even in these cases about 50% of the patients will fully recover. Of the remaining 50% about half of those will retain some mildly disabling after-effects, while the other one-half will show signs of permanent disability. Special devices may have to be used in these cases, such as an iron lung to assist in breathing when the respiratory system is impaired by the disease.

A form of the disease that can be fatal is the kind that leads to a paralysis of the muscles in the throat. This type of paralysis can lead to the regurgitation of the gastric juices into the respiratory system thus causing it to shut down. The large majority of these cases (80%) can still recover through proper treatment. This complication of the disease is known as bulbar poliomyelitis.

Because infants in underdeveloped parts of the world may have built up immunity from their mothers who had been exposed to the virus, there has been a belief that these children were less at risk of contracting polio than children in advanced countries with improved sanitation. Demographic statistics of incident rates, however, tend to raise questions about the effectiveness of natural, infant immunities developing in backward countries. Immunization programs against poliomyelitis as well as other common childhood diseases is still carried on by the World Health Organization as the only reliable way of eradicating the disease.

In the 1950s two types of vaccines were developed in the United States. One type, the Salk vaccine , named after its developer Jonas Salk, used dead polio viruses that were injected. The other type is called the Sabin vaccine, after Albert Sabin, and is an oral vaccine using a weaker strain of the polio viruses for immunity.

Since both vaccines are effective against all three strains of the polio viruses, there has been a virtual eradication of the disease in the United States and other countries that are able to employ a successful immunization program for their populations.

For those who contracted the disease before the vaccination programs became fully effective there have been reports of a disorder which is referred to as post-polio syndrome . This condition is characterized by fatigue, pains in the joints and muscles, problems with breathing, and a loss of muscle strength. Physical and occupational treatment therapies have been developed to deal with this problem.

Incubation and natural immunity

The term infantile paralysis for poliomyelitis was appropriate to the extent that the majority of cases, 70-90%, do occur in early childhood, below the age of three. In countries with temperate climates the infection rate rises seasonally during the heat and humidity of the summer months. The viruses are passed along either orally or through contact with infected feces or even through inhalation of moisture particles from infected individuals, such as by cough.

There may be some peaking of the disease in the tropics, but it is less evident. It takes from four to 35 days for the virus to incubate. Symptoms in most cases will begin to show after one to three weeks after contracting the virus.

The view is still current with some polio epidemiologists (physicians who study ways of preventing the spread of disease) that by the age of six, children in countries with poor sanitation have acquired a permanent immunity to polio, whereas children in countries with good sanitation are more apt to get the disease in their adult years since they were not exposed to it at an earlier period of life. Statistical analysis has left this assumption open to debate.

The iron lung

In the cases of polio that paralyzed the muscles necessary for breathing the so-called iron lung was developed in the mid-1900s. The iron lung is an artificial respirator . The patient's body is enclosed in a metal tank that uses air pressure changes to expand and contract the chest walls. In the 1920s a physiologist named Philip Drinker invented this innovative way of dealing with the respiratory problems of polio patients. The iron lung used a continuous power source which made it superior to existing respirators.

Drinker's original design was improved by physicians to increase the patient's care and comfort. The medical community depended on the iron lung in the treatment of patients with paralysis of the respiratory muscles. It was heavily used during the polio epidemic of 1931. Large, hospital-based respirator centers were developed to care for the many polio patients with respiratory paralysis. These centers were the predecessors of today's intensive care units.

World eradication of polio

The goal for the total eradication of polio, just as small pox has been eliminated, has annually been nearing a reality. About 600,000 cases of polio were reported each year before the introduction and full use of the polio vaccines. That number held firm from the mid-1950s to the early part of the next decade of the 1960s. By 1992 the number of reported cases throughout the world dropped to 15,406. Peru in 1991 was the only country in the western hemisphere to report one case of polio.

There are, however, areas in the world that still are at risk for the transmission of polio viruses. The World Health Organization recommends that immunization of children below the age of five be carried out and that oral polio vaccine be used instead of the Salk type. According to WHO, at least five doses of the oral vaccine should be given door to door on immunization designated days. Networks of clinics and reporting services should also be available to monitor the effective implementation of these immunization drives.

It was the World Health Organization that was responsible for the world eradication of smallpox by waging an 11-year campaign against the virus that caused it, the variola virus . WHO was able to bring countries together to use a vaccine that had been discovered 170 years ago. The polio viruses, however, are still active and there really may be 10 times as much polio in the world than is actually officially reported.

Feasibility for eradication

One of the problems of testing for the eradication of polio infections is that the majority of cases do not show any clinical symptoms. They are asymptomatic. Less than 1% of polio infections lead to paralysis and most of the cases that go on to paralysis are caused by the type 1 poliovirus. Type 1 is also the one most responsible for outbreaks of epidemics. Along with type 3 it represents probably less than one case out of a thousand polio infections.

Another problem in tracking the polio virus is that there are other viruses (Enteroviruses) that create symptoms that are exactly like the ones created by the polio viruses. There are also some unusual types of symptoms in some polio infections that resemble a disorder known as Guillain-Barre syndrome . Only a careful laboratory examination that includes isolating the viruses from the patient's stool can be considered for giving a correct diagnosis of the infection. The presence of such laboratory facilities, especially in backward areas, therefore, becomes an important factor in the program to eliminate infections from polio viruses.

Polio vaccines

In 1955 the Salk inactivated polio vaccine was introduced. It was followed by the Sabin live, attenuated oral vaccine in 1961. These two vaccines have made it possible to eliminate polio on a global level.

The Salk vaccine as it has been presently developed produces a high level of immunity after two or three injections with only minor side-effects. The major defense the Salk vaccine provides against polio viruses is to prevent them from spreading from the digestive system to the nervous system and respiratory system. But it cannot prevent the viruses from entering the intestinal tract. The Salk vaccine has been effective in certain countries, like those in Scandinavia and the Netherlands, where children received a minimum of six shots before reaching the age of 15. Those countries have good sanitation and the major form of spreading the viruses was through respiratory contagion.

In countries that do not have good sanitation, the Sabin vaccine is preferred because as an oral vaccination it is goes straight to the intestinal tract and builds up immunity there as well as in other parts of the body. Those who have received the vaccine may pass on vaccine viruses through the feces to non-vaccinated members of the population, and that spreads the good effects of immunization. There is, however, the rare adverse side-effect of 1 out of 2,500,000 doses of the Sabin vaccine producing a case of poliomyelitis.

The number of doses to achieve a high level of immunity for the Sabin oral vaccine in temperate, economically advanced countries may be two or three. In tropical countries the degree of immunization is not as high against all three types of polio viruses. The effectiveness of the Sabin oral vaccine in tropical countries is improved when it is administered in the cool and dry seasons and when it is given as part of mass campaign where there is a chance of vaccinated persons passing the vaccine virus on to non-vaccinated persons.

Toward the global eradication of polio, the World Health Organization recommends the Sabin oral vaccine for its better performance in creating overall polio immunity, its convenient form of administration, and for its lower cost.

Need for surveillance

For the total eradication of a disease it is necessary to have the mechanisms for determining the existence of even one solitary instance or case of the disease. That means in effect a quick system of reporting and collection of any suspected occurrence of the disease so that laboratory analysis may be made as soon as possible. Health care providers are given the criteria for determining the presence of the disease. In the case of polio the appearance of a certain type of paralysis called acute flaccid paralysis along with the Guillain-Barre syndrome for a child under five or any physician diagnosed case of polio at any age should receive immediate attention.

Within 24-48 hours two stool specimens are collected along with clinical information, other laboratory findings, and information on whether the person has recently traveled. A 60 day follow-up after the onset of the illness should be made to see if there are any paralytic after effects.

Importance of laboratories

Laboratory confirmation of polio viruses requires an efficient network of laboratories. Each WHO region develops a network of laboratories to support the various countries within that area. In these laboratories the staff is trained to isolate and identify the different types of polio viruses. Some countries send specimens to a regional laboratory in a neighboring country. Regional reference laboratories have been set up to tell the differences between vaccine poliovirus from wild poliovirus. A few of these laboratories produce the needed testing agents, do research, and develop training materials for health workers. These laboratories are coordinated with central libraries that contain genotypic information and samples to help in the identification process.

Cost of global eradication

In many of the countries where polio viruses still exist and are transmitted the cost of eradication cannot be afforded. WHO estimates that global polio eradication, with a 10-year effort, may cost as much as a billion dollars. It is argued that countries in the West and those with advancing economies that are free of polio will benefit by the global eradication of poliomyelitis. For example, the United States could save more than $105 million a year on polio vaccine. Money could also be saved by not having to administer the vaccine. The Netherlands suffered an outbreak of polio in 1991-92. It spent more than $10 million controlling this outbreak. More money will also have to be spent for the long-term care and rehabilitation for the survivors of the Netherlands' outbreak. According to the cost-analysis of leading polio epidemiologists, the total cost of eradication could be recovered in savings within a few years of certification that the world is polio-free.

Treatment of post-polio syndrome

For older survivors of previous polio epidemics in the United States and elsewhere there have been a group of related symptoms known as post-polio syndrome.

The amount of exercise recommended for postpolio people has been an issue in question. While it was felt that this syndrome, characterized by muscle atrophy and fatigue, called for some restrictions on exercise because of the weakened condition of the muscles, a more recent view is calling for a reexamination of that position. The newer view is that exercise training of muscles is more important than avoidance of exercise even though it becomes more difficult in the aging process. It is important to maintain a high level of activity as well as the right kind and amount. Studies have shown that postpolio muscles that have lost strength can recover strength with the right kind of exercise.

It is also possible for these people to improve their endurance, but it is important for them not to have expectations that exceed their physical limitations. One criterion that can be followed for improving the strength of a limb is to determine how much function remains in the limb. The strength of the limb should at least remain the same with the exercise, but if it begins to decrease, then it is possible it is being overexerted. Experts in the field of physical rehabilitation maintain that the limb should have at least 15% of normal function before it can be further improved with exercise. If it is below that amount the exercise may not help to improve strength and endurance.

Use of drugs

Drug studies show that using high doses of prednisone, a drug used as an immunosuppressant did not produce added strength or endurance. Amantadine, used for Parkinson's disease and the fatigue of multiple sclerosis, also was not effective. Another drug, Mestinon, however, showed that post-polio people could benefit from its use. Physicians advise their patients to try it for a one month period starting with a small dose and then over a period of a month to build up the dosage. After the full dosage is reached the user should be able to determine whether or not it will help improve symptoms, especially in the area of strengthening weak muscles. It is particularly recommended to deal with fatigue in emergency situations, such as when driving a car when a low dose can carry the person through the activity safely.

Another medication post-polio people have found helpful and which is available at health food stores is LCarnitine. This is a substance that is already present in the muscles and it has been used in Switzerland and Australia . It is now being tried in the United States to help build up strength and endurance in post-polio cases.

Resources

books

Cefrey, Holly, et al. Epidemics: Deadly Diseases ThroughoutHistory (The Plague, AIDS, Tuberculosis, Cholera, Small Pox, Polio, Influenza, and Malaria). New York: Rosen Publishing Group, 2001.

Crofford, Emily, and Steve Michael. Healing Warrior: A Story about Sister Elizabeth Kenny. Minneapolis: Carolrhoda Books, 1989.

Rogers, Naomi. Dirt and Disease: Polio Before FDR. New Brunswick, NJ: Rutgers University Press, 1992.

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

periodicals

Geier, R. "The State of Polio Vaccination In The World. " Toxicology Methods 12, no. 3 (2002): 221-228.

Markel, Howard. "The Genesis of the Iron Lung." Archives ofPediatrics and Adolescent Medicine 146, no. 11 (november 1994): 1174-1181.

Nair, V. Mohanan. "Polio Eradication - Global Initiative" Journal of Public Health Medicine 24, no. 3 (2002): 207-210.

Ortolon, Ken. "Short On Shots." Texas Medicine 98, no. 5 (2002): 30-33.

Schanke. "Mild Versus Severe Fatigue In Polio Survivors." Journal of Rehabilitation Medicine 34, no. 3 (2002): 134-140.

Jordan P. Richman

KEY TERMS

Acute flaccid paralysis

—An early symptom of poliomyelitis, characterized by weakening or loss of muscle tone.

Guillain-Barre syndrome

—A rare disorder of the peripheral nerves that causes weakness and paralysis, usually caused by an allergic reaction to a viral infection.

Iron lung

—An artificial respirator developed in the twenties and widely used throughout the polio epidemics in the United States and other countries of the thirties and thereafter.

L-Carnitine

—A health food substance being used by some postpolio people.

Post-polio syndrome

—A group of symptoms experienced by survivors of the polio epidemics before the period of vaccination.

Sabin vaccine

—The oral polio vaccine developed by Albert Sabin from weakened live polio viruses and introduced in 1961; the vaccine WHO recommends for immunization programs.

Salk vaccine

—The polio vaccine introduced by Jonas Salk in the mid–1950s using dead polio viruses by injection.

Smallpox

—A viral disease with a long history which in 1980 WHO announced was eradicated as a result of an effective worldwide immunization program.

Wild polio virus

—As opposed to vaccine polio viruses, which are transmitted as a result of the Sabin vaccine, wild polio viruses are those naturally circulated from natural sources of contagion.

World Health Organization

—A body of the United Nations formed in 1948 to manage world health problems, such as epidemics.

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 4–8% 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 1–2% 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 2–10 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 (1914–1995) 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 (1906–1993) 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, 5–10% 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 15–30% 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 1980–1998, 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): 366–369.

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. [email protected]. <http://www.who.int>.

Brian Douglas Hoyle, PhD

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 .

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 (1893–1977) 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 (1914–1995) 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 (1906–1993) 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 ]