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 1 in 200 cases. Polio is also called poliomyelitis.
The infection spreads through direct contact with virus particles that are shed from the throat or in feces. The disease has been virtually wiped out in the Western hemisphere since the introduction of the inactivated vaccine in 1955 and the oral, live vaccine in 1961. 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; by 1998, only 50 countries contained endemic polio; by 2002, only 6 countries still had locally circulating infection. There were 1,265 confirmed cases of polio worldwide in 2004. Today, 90% of all endemic polio is contained within India, Nigeria and Pakistan. In developing countries, some people remain unvaccinated. Poor sanitation and poor hygiene promote the spread of the virus. People traveling to these areas of the world must have up-to-date immunizations. The World Health Organization is attempting to eradicate polio worldwide, as it did with smallpox.
Though rare, polio has been caused when people are immunized with the live polio vaccine. Countries that have wiped out polio usually use the inactivated polio vaccine, which never causes polio.
There are two forms of polio:
Minor poliomyelitis (also called abortive poliomyelitis) occurs primarily in young children, and is the more common of the two forms. 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 is a more severe illness that develops approximately 7 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 occur, but paralysis does not continue to get worse afterwards. The disease most commonly affects the strength of muscles of the legs. It can also affect strength in the muscles of the arms and abdomen. When polio affects strength in the muscles of the neck and throat, it causes difficulty speaking and swallowing. The most life-threatening form of polio causes weakness of the muscles in the chest that are needed for breathing. The virus also can sometimes affect the parts of the brain that control breathing. When a polio victim develops breathing trouble, they need machines to help breathe for them.
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. The poliovirus can be detected in throat or stool samples. Antibodies to the virus can be detected in the blood.
Recovery from minor polio occurs in about three days. The fever and other symptoms of major polio 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 the American Academy of Pediatrics and the Advisory Committee on Immunization Practices in 2009:
- 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 are received in a combination vaccine, these doses should be given on the same schedule, substituting for a polio vaccine that is given separately.
- You are considered fully protected against polio if you have had at least three doses of IPV, at least three doses of 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 living in the United States who have never been vaccinated, vaccination is recommended before traveling to areas where polio exposure is possible (such as India, Pakistan, Afghanistan and Nigeria).
- Vaccination is recommended for previously unvaccinated health care workers, who have close contact with patients who might be excreting wild polioviruses. Vaccination also is recommended for laboratory workers who handle specimens that may contain polioviruses.
- A first dose of IPV should be followed by a second dose 4 to 8 weeks later. Ideally, a third dose should be given 6 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.
No drug can kill the virus once an infection has begun. Treatment is directed at controlling the symptoms of the disease. People with minor poliomyelitis are treated with bed rest and over-the-counter medicines to control fever and muscle aches.
People with major poliomyelitis may require additional treatments, including:
- Physical therapy - Therapy helps to minimize damage to paralyzed muscles and to help people regain mobility as the acute illness resolves. 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 not empty completely. This can lead to urinary infections. Using catheters to empty the bladder may be necessary, and long-term use of antibiotics is recommended in some cases.
- Mechanical breathing support - When polio weakens the chest muscles so much that they cannot move the lungs (cannot breathe), people can be kept alive by placing a tube into their windpipe (the trachea). This tube is placed through an opening in the neck, called a tracheostomy. Breathing is performed by a machine called a ventilator that moves air in and out of the lungs. A catheter attached to a suction motor can 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.
Seek medical attention for any signs of muscle weakness or paralysis, particularly when accompanied by a fever. Severe headache with stiff neck and back also require medical attention. For people who live in the United States and most other developed nations, such symptoms are unlikely to be caused by poliovirus. However, they could indicate infection with another virus, and always require prompt medical attention.
People with minor illness and nonparalytic forms of polio recover completely, and most people with major illness who were paralyzed also recover completely. Fewer than 25% of people with polio are disabled for life.
Even though you can recover completely from polio symptoms, polio leaves behind some damage. As you age, your nervous system may become less able to compensate for the damage that polio caused, so symptoms may gradually reappear. This can happen 15 or 30 years after the polio infection was active. Recurring symptoms from polio are called post-polio syndrome.
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