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Polio is a highly contagious illness that is caused by infection with the poliovirus -- at one time, it was one of the most dreaded childhood diseases of the 20th century in the United States. However, thanks to the introduction of the vaccine, the number of cases has decreased dramatically. It is important to note that up to 95 percent of people infected with the poliovirus have no symptoms. There is no cure for the disease, but most people recover without any long-term problems.

What Is Polio?

Polio is an infectious disease that is caused by a virus. It used to be very common in the United States. The disease caused severe illness in thousands of people each year before the vaccine was introduced in 1955. Polio is also known as poliomyelitis or infantile paralysis.

What Causes It?

The cause of the disease is an infection with the poliovirus, which is a single-stranded RNA virus from the family Picornaviridae and genus enterovirus.
Poliovirus only infects humans. It is more common during summer months in temperate climates. In tropical climates, there is no seasonal pattern. There are three types of poliovirus (known as serotypes), which include P1, P2, and P3.
(Click Cause of Polio for more information about the cause of this disease.)

How Is It Spread?

Polio is a highly contagious illness that can spread easily from person to person. In fact, when a person is infected, it is expected that transmission among susceptible household contacts will occur in nearly 100 percent of children and over 90 percent of adults.
When a person is infected, the virus resides in the intestinal tract and mucus in the nose and throat. Poliovirus is most often spread through contact with stool of this infected person (known as fecal-oral transmission). Less frequently, transmission can occur through contact with infected respiratory secretions or saliva (oral-oral transmission).
(Click How Is Polio Spread? for more information about transmitting the disease.)
Written by/reviewed by:
Last reviewed by: Arthur Schoenstadt, MD
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