What Is It?
Poliomyelitis, commonly called polio, is a highly contagious infection caused by the poliovirus. In a small percentage of infected people, the virus attacks nerve cells in the brain and spinal cord, particularly the nerve cells in the spinal cord that control muscles involved in voluntary movement such as walking. Destruction of these neurons causes permanent paralysis in one in 200 cases.
The infection is spread through direct contact with virus particles that are shed from the throat or in feces. The disease was virtually eradicated in the Western hemisphere after the introduction of the inactivated vaccine in 1955 and the oral, live vaccine in 1961. It is anticipated that polio will soon be eradicated worldwide. Vaccination campaigns have succeeded in reducing the number of countries where polio is endemic (where it occurs locally). In 1988, more than 120 countries contained endemic poliovirus. In 1998, 50 countries contained endemic polio, and in 2002, only six countries still had locally circulating infection. Today, 90 percent of all endemic polio is contained within India, Nigeria and Pakistan. However, in developing countries, some individuals remain unvaccinated, and poor sanitation and poor hygiene promote spread of the virus. People traveling to these areas of the world must have up-to-date immunizations.
Today polio occurs in developed countries only as a rare complication of immunization with the live polio vaccine. Paralytic poliomyelitis caused by the live vaccine has become even more rare recently because countries that have eradicated polio are switching to the inactivated polio vaccine, which never causes the disease.
Today poliomyelitis occurs in the United States only as a rare complication of immunization with the live polio vaccine. Approximately five to 10 cases are reported each year, half of them in vaccine recipients — usually infants receiving their first dose of the vaccine. Most other cases occur in people in close contact with immunized infants; children or adults with weakened immune systems are especially vulnerable.
There are two forms of polio illness:
- Minor poliomyelitis (also called abortive poliomyelitis), which occurs primarily in young children, is the most common of the two. The illness is mild and the brain and spinal cord are not affected. Symptoms appear three to five days after exposure to the virus, and include slight fever, headache, sore throat, vomiting, lack of appetite and a general feeling of illness and discomfort.
- Major poliomyelitis (also called paralytic and nonparalytic polio) is a more severe illness that develops approximately seven to 14 days after exposure to the virus. Symptoms include fever, severe headache, stiff neck and back, and deep muscle pain. Some people experience temporary abnormalities of skin sensation. Muscle spasms and a tendency to retain urine are common. Muscle weakness and paralysis may develop rapidly or gradually during the time fevers are occurring, but paralysis does not continue to get worse afterwards. The disease most commonly affects the muscles of the legs, but the areas affected depend upon what portion of the spinal cord is damaged, and can include the arms, abdominal muscles, chest, neck and throat muscles. Respiratory failure occurs if the virus infects the nerves in the spinal cord that control the respiratory muscles of the chest, or the parts of the brain involved in respiration.
The diagnosis of polio is based on a neurological exam. Your doctor may suspect that you have polio if you have fever with limb weakness or paralysis that mainly affects one side of your body. Your doctor will test your muscle reflexes and look for muscle weakness, abnormal muscle contractions and decreased muscle tone. Throat or stool samples may be used to identify the poliovirus with laboratory tests. Blood tests also may be used to identify antibodies to the virus that are produced by your immune system if you have the infection.
Recovery from minor poliomyelitis occurs in about three days. The fever and other symptoms of major poliomyelitis can go away within days, but paralysis can be permanent. Some muscle function may return during the first six months after the acute illness, and improvement can continue for two years.
Depending on where they live, infants and children should be immunized with one or both forms of the polio vaccines: the Salk inactivated poliovirus vaccine (IPV), which is given by injection, or the Sabin live attenuated oral polio vaccine (OPV), which is given by mouth. OPV provides the best protection against polio. However, in rare cases, it can cause paralytic polio. For this reason, some countries where polio is no longer endemic now use only the inactivated polio vaccine, which is almost as effective. In the United States, the vaccination schedule recommended by both the American Academy of Pediatrics and the Advisory Committee on Immunization Practices was updated in 2000. The schedule is as follows:
- IPV for all children at 2 months, 4 months, 6 to 18 months, and 4 to 6 years of age.
- Combination vaccines are being developed to reduce the number of injections that children must have. In the event that one or more doses of IPV is received in a combination vaccine, these doses should be given on the same schedule, substituting for polio vaccine that is given separately.
- You are considered to be fully protected against polio if you have had at least three doses of inactivated poliovirus vaccine (IPV), at least three doses of live oral poliovirus (OPV), or any combination of three IPV and OPV doses. Because polio is now less common, not all adults require full immunization if they did not receive the vaccines in childhood.
- For adults who have never been vaccinated, vaccination is recommended before traveling to areas where there is persistently endemic polio. Vaccination also is recommended for previously unvaccinated health-care workers. A first dose of IPV should be followed by a second dose four to eight weeks later. Ideally, a third dose should be given six to 12 months after the second dose, but it can be given as soon as four weeks after the second dose if this is needed so that a traveler can get all three doses before leaving on a trip.
There is no drug that kills the virus once an infection has begun. Treatment is directed at the symptoms of the disease. People with minor illness or nonparalytic major forms of the disease are treated with bed rest and over-the-counter medicines to control fever and muscle aches.
Major, paralytic forms of the disease may require additional treatments, including:
- Physical therapy — Physical therapy prevents further damage to paralyzed muscles. Treatment for paralysis depends on which muscles are affected.
- Measures to prevent urinary-tract infections — If the bladder muscles do not contract normally, the bladder may empty incompletely. This can promote urinary infections. The use of catheters to empty the bladder may be necessary, and long-term use of antibiotics is recommended in some cases.
- Mechanical breathing support — Some people have problems keeping their airways open for breathing after polio infection. In this case, a rigid tube can be placed into the trachea (the windpipe that connects the mouth to the bronchial tubes in the lungs). This tube is placed through an opening in the neck, called a tracheostomy. A tracheostomy tube also may be needed if the respiratory muscles are weak or paralyzed. In this case, the tracheostomy tube can receive breaths of air from a machine called a ventilator. A catheter attached to a vacuum (suction) motor can be used to remove excessive mucus through the tracheostomy tube. People who need artificial respiration long-term must live in a facility that is staffed by nurses and therapists who are skilled in respiratory care.
When To Call A Professional
Seek medical attention for any signs of muscle weakness or paralysis, particular when accompanied by a fever. Severe headache with stiff neck and back also require medical attention.
People with minor illness and nonparalytic forms of poliomyelitis recover completely, and most people with major illness who were paralyzed also recover completely. Less than 25 percent of people with polio are disabled for life.
Diseases and Conditions Center
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.