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.