Polio (also called poliomyelitis) is a contagious, historically devastating disease that was virtually eliminated from the Western hemisphere in the second half of the 20th century. Although polio has plagued humans since ancient times, its most extensive outbreak occurred in the first half of the 1900s before the vaccination created by Jonas Salk became widely available in 1955.

At the height of the polio epidemic in 1952, nearly 60,000 cases with more than 3,000 deaths were reported in the United States alone. However, with widespread vaccination, wild-type polio, or polio occurring through natural infection, was eliminated from the United States by 1979 and the Western hemisphere by 1991.

Signs and Symptoms

Polio is a viral illness that, in about 95% of cases, actually produces no symptoms at all (called asymptomatic polio). In the 4% to 8% of cases in which there are symptoms (called symptomatic polio), the illness appears in three forms:

1. a mild form called abortive polio (most people with this type may not even suspect they have it because their sickness is limited to mild flu-like symptoms such as mild upper respiratory infection, diarrhea, fever, sore throat, and a general feeling of being ill)
2. a more serious form associated with aseptic meningitis called nonparalytic polio (1%-5% show neurological symptoms such as sensitivity to light and neck stiffness)
3. a severe, debilitating form called paralytic polio (this occurs in 0.1%-2% of cases)

People who have abortive polio or nonparalytic polio usually make a full recovery. However, paralytic polio, as its name implies, causes muscle paralysis — and can even result in death.

In paralytic polio, the virus leaves the intestinal tract and enters the bloodstream, attacking the nerves (in abortive or asymptomatic polio, the virus usually doesn't get past the intestinal tract). The virus may affect the nerves governing the muscles in the limbs and the muscles necessary for breathing, causing respiratory difficulty and paralysis of the arms and legs.

Contagiousness

Polio is transmitted primarily through the ingestion of material contaminated with the virus found in stool (poop). Not washing hands after using the bathroom and drinking contaminated water were common culprits in the transmission of the disease.

Prevention

In the United States, it's currently recommended that children have four doses of inactivated polio vaccination (IPV) between the ages of 2 months and 6 years.

By 1964, the oral polio vaccine (OPV), developed by Albert Sabin, had become the recommended vaccine. OPV allowed large populations to be immunized because it was easy to administer, and it provided "contact" immunization, which means that an unimmunized person who came in contact with a recently immunized child might become immune, too.

The problem with OPV was that, in very rare cases, paralytic polio could develop either in immunized children or in those who came in contact with them. Since 1979 (when wild polio was eliminated in the United States), the approximately 10 cases per year of polio seen in this country were traced to OPV.

IPV is a vaccine that stimulates the immune system of the body (through production of antibodies) to fight the virus if it comes in contact with it. IPV cannot cause polio.

In an effort to eradicate all polio, including those cases associated with the vaccine, the Centers for Disease Control and Prevention (CDC) decided to make IPV the only vaccine given in the United States. Currently, the CDC and American Academy of Pediatrics (AAP) recommend three spaced doses of IPV given before the age of 18 months, and an IPV booster given between the ages of 4 to 6, when children are entering school.

If you're planning to travel outside the United States, particularly to Africa and Asia (where polio still exists), be sure that you and your kids have received a complete set of polio vaccinations.

Duration

Although the acute illness usually lasts less than 2 weeks, damage to the nerves could last a lifetime. In the past, some patients with polio never regained full use of their limbs, which would appear withered. Those who did fully recover might go on to develop post-polio syndrome (PPS) as many as 30 to 40 years after contracting polio. In PPS, the damage done to the nerves during the disease causes an acceleration of the normal, gradual weakness due to aging.

Treatment

During the height of the polio epidemic, the standard treatment involved placing a patient with paralysis of the breathing muscles in an "iron lung" — a large machine that actually pushed and pulled the chest muscles to make them work. The damaged limbs were often kept immobilized because of the confinement of the iron lung. In countries where polio is still a concern, ventilators and some iron lungs are still used.

Historically, home treatment for paralytic polio and abortive polio with neurological symptoms wasn't sufficient. However, asymptomatic and mild cases of abortive polio with no neurological symptoms were usually treated like the flu, with plenty of fluids and bed rest.

The Future of Polio

The World Health Organization (WHO) is working toward eradicating polio throughout the world. Significant strides have already been made. In 1988, 355,000 cases of polio in 125 countries were reported. By the end of 2004, there were just 1,255 cases.

Four countries (Afghanistan, India, Nigeria, and Pakistan) still have polio circulating, and the virus could be introduced to other countries. If the polio virus is imported into a country where not enough people have been immunized, there's the risk that it could spread from person to person. That's what has happened in some countries in Africa and Asia. So until it has been eliminated worldwide, it's important to continue vaccinating kids against polio.

Reviewed by: Joel Klein, MD
Date reviewed: September 2010