Poliomyelitis

B

Nonparalytic Poliomyelitis

Poliovirus infection of nerve cells sometimes results in nonparalytic poliomyelitis—that is, polio without paralysis. Patients with nonparalytic polio experience the fever and other symptoms of abortive poliomyelitis. In addition, they typically feel pain and stiffness in the neck and back. They also may develop aseptic meningitis—inflammation of the membranes that surround the brain and spinal cord. Symptoms from nonparalytic polio usually subside within a week without causing lasting damage.

C

Paralytic Poliomyelitis

In about 1 or 2 percent of poliovirus infections, paralytic poliomyelitis, a disabling form of the disease, occurs. The virus infects motor neurons (nerve cells that send signals to muscles) in the spinal cord and damages or destroys them. The muscles that the neurons activate become painful and weak. Paralysis begins when the muscle is no longer able to move. Roughly 2 to 5 percent of infants who develop paralytic polio die. For adults the disease is even deadlier, causing death in 15 to 30 percent of cases.

Which muscles are affected and the extent of the paralysis depend on the part of the spinal cord the poliovirus invades and the number of nerves affected. The legs or arms are most often affected, and one side or both sides of the body may be involved. The older the person is when polio strikes, the more likely extensive paralysis becomes. In some cases paralysis of muscles that control breathing occurs, requiring mechanical breathing assistance (see Artificial Respiration).

In the most serious cases of paralytic polio, the virus attacks the brainstem, causing bulbar poliomyelitis. This type of polio can affect nerves that send signals to the ears, eyes, and the muscles controlling chewing and swallowing. Sometimes the virus affects the part of the brain that controls the rate of breathing and the heartbeat, resulting in death.

---

---

IV

Diagnosis and Treatment of Polio

Doctors diagnose polio by isolating the virus in throat cultures, stool samples, or samples of cerebrospinal fluid (the fluid that surrounds the brain and spinal cord) taken from an infected person. Blood tests that identify antibodies to the poliovirus also confirm a diagnosis.

As yet there is no cure for polio—no drug or other medical treatment can halt the destructive action of the disease. However, medical treatment can lessen the severity of symptoms and prevent complications. Simple treatments, including moist heat applied to affected muscles, can ease pain, as can pain-relieving drugs. Antispasmodic drugs can help patients who suffer muscle spasms (involuntary muscle contractions) as a consequence of nerve damage. Strict bed rest was once advised for patients with paralytic polio, but today the only limitations on a patient’s movement are those imposed by the disease itself.

An extremely dangerous complication of paralytic polio develops when nerve damage affects the muscles used in breathing. When polio patients lose the ability to breathe by themselves, they must rely on a mechanical device for artificial respiration. Today, a machine called a ventilator is used. It forces air into the lungs by way of a tube inserted into the upper airway, through the nose, mouth, or a slit in the trachea.

Physical therapy helps patients with paralytic polio stretch and move affected muscles. This movement minimizes the atrophy, or shrinkage, of affected muscles and limbs and builds strength. Exercises can also retrain working muscles to compensate for other muscles that have permanently lost the ability to move. Rehabilitative therapy trains patients to use braces, crutches, and other devices that provide support and aid mobility.

V

Prevention of Polio

Immunization with polio vaccine is the best way to prevent polio. Vaccines work by exposing the body’s immune system to a microbial infection that is strong enough to provoke an immune response but not severe enough to result in full-blown illness. In response to the infection, the immune system produces antibodies to fight the infectious agent. Once the body has overcome the challenge of the vaccine-induced infection, the antibodies can recognize and quickly handle any subsequent invasion by the same agent (see Immunization).

Scientists use two main strategies for producing a vaccine, and both methods have been successfully employed against polio. One strategy uses quantities of virus that have been inactivated, or killed. This form of the polio vaccine is administered by injection. The other vaccine strategy uses live virus that scientists grow in a laboratory and systematically weaken so that it no longer causes serious infection. This form of polio vaccine, known as oral polio vaccine, is administered by mouth, either in a drink or in a sugar cube or other food. The oral vaccine is easier to administer than the injected vaccine, particularly in remote areas that lack trained medical staff or proper hospital facilities.

The live poliovirus used in the oral polio vaccine involves some slight risk. There is a chance that a dose may contain improperly weakened virus that is still capable of causing illness. In the 1990s the risk of contracting paralytic polio from oral polio vaccine was 1 in approximately 2.4 million doses of vaccine.

Successful immunization programs virtually wiped out the disease in North America, Latin America, and Europe. But the struggle to eradicate polio continues in some developing nations. Furthermore, health officials stress that vaccination programs must be maintained in areas considered polio free. They warn that the poliovirus could easily become dangerous again among children who have not acquired immunity. This danger was chillingly demonstrated in 1979 when an outbreak of paralytic polio erupted among unvaccinated members of Amish communities in Pennsylvania and Maryland.

A

Post-Polio Syndrome

Some people who had paralytic polio develop new symptoms years later, a condition known as post-polio syndrome (PPS). Anywhere from 25 to 50 percent of these paralytic polio survivors grapple with PPS decades after their original illness, according to estimates by the National Institutes of Health. The cause of PPS is unknown, and there is no treatment available.

Common symptoms of PPS include lessened endurance, fatigue, or exhaustion, after even minor activity; weakness and pain in muscles, even in those that seemed unaffected by the original illness; and joint pain. The symptoms persist and gradually worsen. People with PPS may also experience sleep difficulties, including sleep apnea; difficulty swallowing; muscle twitches and other symptoms. For some people the symptoms are mild, while for others they become severe as the muscles atrophy (waste away).

Although medical experts do not know the exact cause of PPS, there is a widely accepted theory to explain the loss of muscle function. According to this theory, after nerve cells are damaged or destroyed during the original illness, the surviving nerve cells seek to compensate for this loss by growing new nerve endings, or muscular connections, to restore muscle function. However, these new connections appear to wear out after years of overwork, producing the symptoms of PPS. Another possible source of the problem is that the undamaged limb or limbs have overcompensated for the damaged limb or limbs for many years.

Post-polio syndrome is not life threatening, but it can limit mobility and interfere with daily activities. There is no treatment for PPS. Physical therapy can help strengthen muscles, and pain medications can ease pain. Most experts advise people with PPS to pace their exertion through the day and simplify their activities wherever possible.