A Devastating
Disease: Polio
By Deshae Gehr
The Poliovirus
 Causes disease Poliomylitis, literally meaning
“gray spinal cord inflammation
 It is a virus
 There are three types of poliovirus and many
strains of each type
 It is contagious: usually spread from person to
person.
 Only harmful to humans
What is a virus?
 A pathogen that is not actually
living (debated)
 Depends on a host cell to live
 Contains genetic material
(RNA) enclosed by a capsid
that protects the viral genetic
material until it cann find a
host
 Inserts genetic material into
host cells, and uses cell to
manufacture more viruses.
 Destroys cell when new
viruses burst out
Lytic vs. Lysogenic
 Lytic:
 When a dormant
virus is stimulated
and it begins to use
the cell to
manufacture new
viruses, ultimately
killing it.
 Lysogenic:
 When viruses remain
dormant inside host
cells for a period of
time
Overview:
 Poliomylitis is caused by the poliovirus which
belongs to the genus Enterovirus.
 They contain RNA, and target the gastrointestinal
tract
 Structure: it is a single RNA genome enclosed in a
protein shell (capsid).
 There are 3 groups of polioviris:
 Poliovirus type 1, 2, and 3
 Each has a slightly different capsid protein
 PV1 is the most common, and most closely
associated with paralysis
Polio
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4 different kinds: Spinal, bulbar,bulbospinal, paralytic
All can result in paralysis of different parts of the body
Poliovirus spreads along certain nerve fiber pathways destroying motor
neurons within the spinal cord, brain stem, or motor cortex.
This leads to the development of paralytic poliomyelitis in certain parts of
the body, depending on where the central nervous system is damaged,
Inflammation associated with nerve cell destruction often alters the color
and appearance of the gray matter in the spinal column causing it to
appear reddish and swollen
The likelihood of developing paralytic polio increases with age
Severity of paralysis also increases
Paralysis in children occurs in only 1 in 1000 cases.
In adults, paralysis occurs in 1 in 75 cases
(http://en.wikipedia.org/wiki/Poliomyelitis#Cause)
Early Symptoms:
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high fever
Headache
Stiffness (back and neck)
weakness of various muscles
sensitivity to touch
difficulty swallowing
muscle pain
loss of reflexes
Irritability
Constipation
difficulty urinating
Paralysis develops 1-10 days after early symptoms begin
Usually continues for 2-3 days, and complete soon after
How polio enters the body:
 The virus enters through the mouth
 It multiplies in the throat and gastrointestinal tract
 It gets into the bloodstream and is carried to the
central nervous system
 It replicates there
 It attacks motor neuron cells, ultimately killing
them.
 (Motor neurons control muscles for swallowing,
circulation, respiration, and the trunk, arms, and
legs)

http://americanhistory.si.edu/polio/virusvaccine/how.htm
Attaching to the cells:
 Human nerve cells have a protruding protein
structure on their surface
 The polio virus comes in contact with the nerve
cells, the protruding proteins act as receptors and
attach to the cell
 The virus injects its genetic material (RNA) into
the cell, causing the cell to become an assembly
line for manufacturing new viruses. (see slide on
how viruses work)
 The polio virus usually enters the lytic cycle
 1. Polio virus
approaches nerve cells
vai bloodstream
 2. nerve cell receptors
attach to virus.
 3. viral capsid breaks to
release RNA.
 4/5.RNA takes over
ribosomes: cell’s protein
assembly, to make more
viruses.
 6/7. Newly manufactured
viruses burst out of cell
(killing it) and they move
on to new nerve cells
http://americanhistory.si.edu/polio/virusvaccine/how.htm
Polio: Transmission
 Polio is highly contagious
 Spread from human contact
 Transmitted in fecal-oral manner (generally
occurs when food or water is contaminated), or
oral to oral manner
 Its incubation period is anywhere from 3 to 35
days
 Most contagious 7-10 days before, and 7-10
days after
Polio: Transmission
 It was very prevalent among children,
although anyone can get it, especially
those with compromised immune systems
 Climate has been known to affect the
transmission
 Temperate climates: with this climate the
transmission peak for polio is in the summer and
fall.
 However, with tropical climates the seasonal gap is
not as noticable
Treatment:
 There is no cure for polio
 Treatment is lessening severity of the symptoms (of
weakness, paralysis)
 Some examples:
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antibiotics to prevent infections in weakened muscles
Pain-relieving drugs
moderate exercise and a nutritious diet
Long-term rehabilitation; physical therapy
Braces (body)
Corrective shoes
Orthopedic surgery
Iron lungs (portable ventilators)
The Vaccine:
 Now there is a vaccine developed in 1952
by Jonas Salk
 Albert Sabin later developed an oral polio
vaccine
 Vaccines work by exposing the person to
the virus in a controlled fashion so the body
creates antibodies, that result in immunity.
Polio: History
 Polio is a disease that
has existed since
Egyptian times or before
 The 1st known clinical
description is reported in
1780 by English
physician, Michael
Underwood
 1st seen as a distinct
condition in 1840 by
Jakob Heine.
 Jakob Heine
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http://upload.wikimedia.org/wikipedia/en/2/2e/Jakobheine.jpg
Polio: History
 Polio was a devastating
disease in the 20th century,
particularly in the United
States and Europe.
 Populations exposed to
poor sanitation had
become immune to the
virus over time
 However, developing
countries were
increasingly getting better
sanitation
 The natural immunity built
up due to constant
exposure made the
general population more
at risk (esp. 6 month-olds
to 4 year-olds)
Polio: History
 Polio infections rapidly increased in new
age countries beginning in 1900.
 The rate of death and paralysis from polio
also increased drastically
 1952: United States, had the worst epidemic
in the nation's history.
 58,000 reported cases: 3,145 died; 21,269
were left with mild to disabling paralysis
 http://www.ucmp.berkeley.edu/alllife/virus.html
 http://en.wikipedia.org/wiki/Poliomyelitis
 http://kidshealth.org/parent/infections/bacterial_viral/pol
io.html
 http://upload.wikimedia.org/wikipedia/en/2/2e/Jakobhei
ne.jpg
 http://americanhistory.si.edu/polio/virusvaccine/how.ht
m