Poliovirus is a highly contagious virus that can spread easily from person to person. In fact, when a person is infected with poliovirus, it is expected that polio transmission among susceptible household contacts will occur in nearly 100 percent of children and more than 90 percent of adults.
When a person is infected with poliovirus, the virus resides in the intestinal tract and mucus in the nose and throat. Transmission of this virus most often occurs through contact with stool of this infected person (known as fecal-oral transmission). Less frequently, it can be spread through contact with infected respiratory secretions or saliva (oral-oral transmission).
Following infection with the virus, a person does not immediately become sick. Once poliovirus enters the body, it travels to the back of the throat, nose, and intestines, where it begins to multiply. It can also travel to other parts of the body. Symptoms of polio usually appear after 7-14 days. This period between poliovirus transmission and the beginning of polio symptoms is called the polio incubation period. The polio incubation period can be as short as 4 days or as long as 35 days.
Up to 95 percent of people who are infected with poliovirus will have no symptoms of polio. However, infected people who do not have polio symptoms can still spread the poliovirus and cause others to develop polio.
(Click Polio Transmission for more information on how polio is transmitted or Poliomyelitis Symptoms for more information on polio symptoms and signs.)
How Common Is It?
At one time, poliovirus infection occurred throughout the world. Transmission of wild poliovirus was interrupted in the United States in 1979, or possibly earlier. A polio eradication program conducted by the Pan American Health Organization led to elimination of polio in the Western Hemisphere in 1991.
The Global Polio Eradication Program has dramatically reduced poliovirus transmission throughout the world. In 2003, only 784 confirmed cases of polio were reported globally, and polio was endemic in six countries.