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Poliomyelitis
What is Polio?
Poliomyelitis (polio) is a highly infectious disease caused
by a virus. It invades the nervous system, and can cause total
paralysis in a matter of hours. It can strike at any age, but
affects mainly children under three (over 50% of all cases).
The virus enters the body through the mouth and multiplies
in the intestine. Initial symptoms are fever, fatigue, headache,
vomiting, stiffness in the neck and pain in the limbs. One
in 200 infections leads to irreversible paralysis (usually
in the legs). Amongst those paralysed, 5%-10% die when their
breathing muscles become immobilized. Although polio paralysis
is the most visible sign of polio infection, fewer than 1%
of polio infections ever result in paralysis. Poliovirus can
spread widely before cases of paralysis are seen. As most people
infected with poliovirus have no signs of illness, they are
never aware they have been infected. After initial infection
with poliovirus, the virus is shed intermittently in faeces
(excrement) for several weeks. During that time, polio can
spread rapidly through the community.
Who is most at risk of polio?
Polio mainly affects children under five years of age. However,
immune and or partially immune adults and children can still
be infected with poliovirus and carry the virus for long enough
to take the virus from one country to another, infecting close
contacts and contaminating sanitation systems. This could facilitate
transmission especially in countries where sanitation systems
are sub-standard.
How is polio spread?
In the remaining polio endemic countries, poliovirus is mainly
passed through person-to-person contact. Most people infected
with the poliovirus do not develop polio paralysis or other
symptoms of polio infection. However one in 200 people do have
symptoms and can become paralyzed. The virus enters the environment
through faeces of people infected then is passed to others
especially in situations of poor hygiene. The poliovirus can
also infect persons who have been vaccinated and can be carried
by them. Such individuals will not develop polio, but can carry
the virus in their intestines and can pass it to others in
conditions of sub-standard hygiene. The disease may infect
thousands of people, depending on the level of sanitation,
before the first case of polio paralysis emerges. Individuals
can carry the virus in their intestines just long enough to
transmit to others. WHO considers a single confirmed case of
polio paralysis to be evidence of an epidemic - particularly
in countries where very few cases occur.
How can polio be prevented?
There is no cure for polio, it can only be prevented through
immunization. Polio vaccine, given multiple times, almost always
protects a child for life. Full immunization will markedly
reduce an individual's risk of developing paralytic polio.
Full immunization will protect most people, however individuals
can still contract the disease due to the failure of some individuals
to respond to the vaccine.
POLIO PARALYSIS
Once established in the intestines, poliovirus can enter the
blood stream and invade the central nervous system - spreading
along nerve fibres. As it multiplies, the virus destroys nerve
cells (motor neurons) which activate muscles. These nerve cells
cannot be regenerated and the affected muscles no longer function.
The muscles of the legs are affected more often than the arm
muscles. The limb becomes floppy and lifeless - a condition
known as acute flaccid paralysis (AFP). More extensive paralysis,
involving the trunk and muscles of the thorax and abdomen,
can result in quadriplegia. In the most severe cases (bulbar
polio), poliovirus attacks the motor neurons of the brain stem
- reducing breathing capacity and causing difficulty in swallowing
and speaking. Without respiratory support, bulbar polio can
result in death.
THE IRON LUNG
Large polio epidemics caused panic every summer during the
1940s and 50s in industrialized countries (US, Western Europe).
At that time, people with polio affecting the respiratory muscles
were immobilized inside "iron lungs" - huge metal cylinders
that operated like a pair of bellows to regulate their breathing
and keep them alive. Today, the iron lung has largely been
replaced by the positive pressure ventilator; nevertheless,
it is still in use in some countries.
Children whose legs are paralysed by polio today often require
crutches, special braces or wheelchairs in order to move
around.
Because no drug developed so far has proven effective, treatment
is entirely symptomatic. Moist heat is coupled with physical
therapy to stimulate the muscles and antispasmodic drugs
are given to produce muscular relaxation. While this can
improve mobility, it cannot reverse permanent polio paralysis.
To read the rest of this article from the World Health Organization,
please click here: http://www.polioeradication.org/disease.asp
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Post-Polio Syndrome
Post-polio
syndrome (PPS) is a condition that affects polio survivors
anywhere from 10 to 40 years after recovery from an
initial paralytic attack of the poliomyelitis virus. PPS
is characterized by a further weakening of muscles that were
previously affected by the polio infection. Symptoms include
fatigue, slowly progressive muscle weakness and, at times,
muscular atrophy. Joint pain and increasing skeletal deformities
such as scoliosis are common. Some patients experience only
minor symptoms, while others develop spinal muscular atrophy,
and very rarely, what appears to be, but is not, a form of
amyotrophic lateral sclerosis (ALS), also called Lou Gehrig's
disease. PPS is rarely life-threatening.
Is
there any treatment?
Presently, no prevention
has been found. Doctors recommend that polio survivors
follow standard healthy lifestyle practices: consuming
a well-balanced diet, exercising in moderation, and visiting
a doctor regularly. There has been much debate about
whether to encourage or discourage exercise for polio
survivors or individuals who already have PPS. A
commonsense approach, in which people use individual
tolerance as their limit, is currently recommended.
What
is the prognosis?
PPS is a very slowly
progressing condition marked by long periods of stability. The
severity of PPS depends on the degree of the residual
weakness and disability an individual has after the original
polio attack. People who had only minimal symptoms from
the original attack and subsequently develop PPS will
most likely experience only mild PPS symptoms. People
originally hit hard by the polio virus, who were left
with severe residual weakness, may develop a more severe
case of PPS with a greater loss of muscle function, difficulty
in swallowing, and more periods of fatigue.
To read the rest of this article from the
National Institute of Neurological Disorders and Stroke (NINDS)
, please click here: http://www.ninds.nih.gov/disorders/post_polio/post_polio.htm
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