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.
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.)
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).
A person who is infected can spread polio about 7-10 days before symptoms begin. A person can continue to spread the disease for about three to six weeks after the beginning of symptoms. However, a person is most contagious for the 7-10 days after symptoms have begun.
Following transmission, a person does not immediately become 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 7-14 days (on average), symptoms can begin. This period between transmission and the beginning of signs and symptoms is called the incubation period. The incubation period can be as short as 4 days or as long as 35 days.
Up to 95 percent of people who are infected have no symptoms. However, infected people who do not have symptoms can still spread the virus and cause others to develop the disease.
If a person does develop symptoms, the symptoms can be categorized into one of three groups, which include:
- Minor polio symptoms (also known as abortive poliomyelitis)
- Aseptic meningitis
- Paralytic poliomyelitis.
In order to make a diagnosis, the doctor will ask the patient a number of questions and perform a physical exam to look for signs and symptoms of the disease.
If the doctor suspects polio, he or she will order certain tests that help to diagnose the disease. These tests will look for the virus or antibodies the body has made against the virus. In order to perform these tests, a stool sample or a throat swab may be taken.
Several other medical conditions can share the signs or
symptoms of polio. The doctor will consider these conditions before making a diagnosis. Some of these conditions include:
Current Treatment for Polio
There is currently no treatment that can kill the virus. Polio is caused by a virus; therefore, antibiotics or other medications are not effective. Instead, treatment focuses on providing relief of symptoms as the body fights the virus. This is called supportive care.
While there is no
cure for polio, most people recover without any long-term problems. Less than 1 percent of infected people will develop permanent paralysis. There is no treatment that can prevent this complication.
The best
cure for polio is preventing it in the first place. Prevention is best accomplished with a vaccine, which is usually given as a shot. Only one kind of vaccine,
inactivated polio vaccine (IPV), is now used in the United States. A live,
oral polio vaccine (
OPV) has not been used in the United States since 2000 but is still used in many parts of the world.
Polio was one of the most dreaded childhood diseases of the 20th century in the United States. There were usually about 13,000 to 20,000 cases of paralytic polio reported each year in the United States before the introduction of the Salk vaccine in 1955. The disease peaked in 1952 when there were more than 21,000 reported cases. The number of cases decreased dramatically following the introduction of the vaccine and the development of a national
polio vaccination program. In 1965, only 61 cases of paralytic polio were reported compared to 2,525 cases reported cases just five years earlier in 1960.
The last cases of naturally occurring paralytic polio in the United States were in 1979, when an outbreak occurred among the Amish in several Midwestern states. From 1980 through 1999, there were 152 confirmed cases of paralytic polio cases reported. Of the 152 cases, eight cases were acquired outside the United States and imported. The remaining 144 cases were vaccine-associated paralytic polio caused by the live oral
polio vaccine.
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