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:
- a mild form called
abortive polio
(most people with this form of polio 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)
- a more serious form associated with aseptic
meningitis
called
nonparalytic polio
(1% to 5% show neurological symptoms such as sensitivity to light
and neck stiffness)
- a severe, debilitating form called
paralytic polio
(this occurs in 0.1% to 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 child 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
In 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.
Six countries (Afghanistan, Egypt, India, Niger, 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:
Steven Dowshen, MD
Date reviewed: December 2007
Originally reviewed by:
Joel Klein, MD
Note: All information is for educational purposes only. For specific medical advice,
diagnoses, and treatment, consult your doctor.
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