The Polio virus

2. • Poliovirus, the causative agent of
poliomyelitis (commonly known as
polio), is a human enterovirus and
member of the family of
Picornaviridae.
• Poliovirus is composed of an
RNAgenome and a protein capsid.
• The genome is a single-
stranded positive-sense RNA
Virus genome that is about
7500 nucleotides long.
• The viral particle is about 30
nm in diameter with
icosahedral symmetry.

3. • Because of its short genome and
its simple composition—only RNA
and a nonenveloped icosahedral
protein coat that encapsulates it,
poliovirus is widely regarded as
the simplest significant virus.
• Poliovirus was first isolated in
1909 by Karl Landsteiner and
Erwin Popper.
• Poliovirus infects human cells by
binding to an immunoglobulin-like
receptor, poliovirus receptor (PVR))
on the cell surface.
• Interaction of poliovirus and PVR
facilitates an irreversible
conformational change of the viral
particle necessary for viral entry.

4. • The virus spreads from person to
person and can invade an infected
person’s brain and spinal cord,
causing paralysis (can’t move parts
of the body).
• The virus enters through the mouth
and multiplies in the throat and
gastrointestinal tract;
• Then moves into the bloodstream
and is carried to the central
nervous system where it replicates
and destroys the Motor Neuron
Cells.
• Motor neurons control the muscles
for swallowing, circulation,
respiration, and the trunk, arms,
and legs.

5. Poliovirus bound to a neuron receptor

6. • Attached to the host cell membrane,
entry of the viral nucleic acid was
thought to occur one of two ways:
a.) Via the formation of a pore in the
plasma membrane through which
the RNA is then “injected” into the
host cell cytoplasm.
b.) Or that the virus is taken up by
receptor-mediated endocytosis
Recent experimental evidence
supports the latter hypothesis
and suggests that poliovirus
binds to CD155 or PVR and is
taken up by endocytosis
• Immediately after
internalization of the particle,
the viral RNA is released.

7. • Released of the viral RNA
Immediately after internalization of
the particle

8. • The primary determinant of
infection for any virus is its ability to
enter a cell and produce additional
infectious particles.
• The presence of (PVR) Polio Virus
Receptor (CD155) is thought to
define the animals and tissues that
can be infected by poliovirus
• Poliovirus is an enterovirus.
• Infection occurs via the fecal–oral
route, meaning that one ingests the
virus and viral replication occurs in
the alimentary tract.
• Virus is shed in the feces of infected
individuals

9. • Poliovirus uses two key
mechanisms to evade the
immune system.
• First, it is capable of surviving
the highly acidic conditions of
the stomach, allowing the virus
to infect the host and spread
throughout the body via the
lymphatic system.
• Second, because it can replicate
very quickly, the virus overwhelms
the host organs before an immune
response can be mounted.
• Individuals who are exposed to
poliovirus, either through infection
or by immunization with polio
vaccine, develop immunity

10. • In immune individuals, antibodies
against poliovirus are present in the
tonsils and gastrointestinal tract
(specifically IgA antibodies) and are
able to block poliovirus replication;
IgG and IgM antibodies against
poliovirus can prevent the spread
of the virus to motor neurons of
the central nervous system.
• When poliovirus encounters
the nerve cells, the protruding
receptors attach to the virus
particle, and infection begins.

11. • Once inside the cell, the virus
hijacks the cell’s assembly process,
and makes thousands of copies of
itself in hours.
• The virus kills the cell and then
spreads to infect other cells.
• For every 200 or so virus particles
that encounter a susceptible cell,
only one will successfully enter and
replicate.
• In tissue culture, poliovirus enters
cells and replicates in six to eight
hours, yielding 10,000 to 100,000
virus particles per cell.

12. • One way the human immune system
protects itself is by producing
antibodies that engage the protein
covering of the poliovirus, preventing
the virus from interacting with
another cell.
• There are three types of poliovirus: 1,
2, and 3. Type 1 is the most virulent
and common.
• Both the Salk and Sabin
vaccines are “trivalent” that is,
active against all three virus
types.

13. • Type 2 poliovirus has not been
detected anywhere in the world
since 1999.
• A person who gets polio is immune
to future infection from the virus
type that caused the polio.

14. • Most people who get infected with
poliovirus (about 72 out of 100) will
not have any visible symptoms.
• About 1 out of 4 people with
poliovirus infection will have flu-like
symptoms that may include
• They include:
 Sore throat, Fever, Tiredness
 Nausea, Headache, Stomach pain
These symptoms usually last 2 to 5
days then go away on their own

15. • A smaller proportion of people with
poliovirus infection will develop other
more serious symptoms that affect the
brain and spinal cord; Including:
 Paresthesia (feeling of pins and
needles in the legs)
 Meningitis (infection of the covering
of the spinal cord and/or brain)
occurs in about 1 out of 25 people
with poliovirus infection
 Paralysis (can’t move parts of the
body) or weakness in the arms, legs,
or both, occurs in about 1 out of
200 people with poliovirus infection.

16. • Paralysis is the most severe symptom
associated with polio because it can
lead to permanent disability and
death.
• Between 2 and 10 out of 100 people
who have paralysis from poliovirus
infection die because the virus affects
the muscles that help them breathe.
• Even children who seem to fully
recover can develop new muscle
pain, weakness, or paralysis as
adults, 15 to 40 years later. This is
called Post-polio Syndrome.
• Note that “poliomyelitis” (or
“polio” for short) is defined as the
paralytic disease. So only people
with the paralytic infection are
considered to have the disease.

17. • Poliovirus only infects humans. It is
very contagious and spreads through
person-to-person contact.
• An infected person may spread the
virus to others immediately before
and about 1 to 2 weeks after
symptoms appear
• The virus lives in an infected person’s
throat and intestines.
• It enters the body through the
mouth and spreads through contact
with the feces (poop) of an infected
person and, though less common,
through droplets from a sneeze or
cough.
• You can get infected with poliovirus
if you have feces on your hands and
you touch your mouth.

18. • The virus can live in an infected
person’s feces for many weeks. It
can contaminate food and water in
unsanitary conditions.
• People who don’t have symptoms
can still pass the virus to others
and make them sick

19. • Polio vaccine protects children by
preparing their bodies to fight the
polio virus.
• Almost all children (99 children out
of 100) who get all the recommended
doses of vaccine will be protected
from polio.
• There are two types of vaccine
that can prevent polio; namely:
a.) Inactivated Poliovirus
Vaccine (IPV)
b.)

20. • Only IPV has been used in the
United States since 2000.
(Given as an injection in the leg or
arm, depending on the patient’s
age).
• OPV is still used throughout much
of the world.

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