The cause of polio is an infection with the
poliovirus. This is a single-stranded RNA virus from the family
Picornaviridae and genus
enterovirus. This virus only infects humans. It is more common during summer months in temperate climates. In tropical climates, there is no seasonal pattern. There are three polioviruses (known as serotypes), which include P1, P2, and P3.
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 with poliovirus, it resides in the intestinal tract and mucus in the nose and throat. The virus 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).
A person who is infected with polio can spread the virus for about seven to ten days before symptoms begin. A person can continue to spread the virus for about three to six weeks after the beginning of symptoms. However, a person is most contagious for the seven to ten days after symptoms have begun.
Following transmission of the virus, a person does not become immediately sick. Once the 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. After 7 to 14 days (on average), symptoms can begin. This period between transmission and the beginning of symptoms is called the
polio incubation period. This period can be as short as 4 days or as long as 35 days.
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