Structure and Characteristics of Polio virus:
1.
Non-enveloped, RNA virus
2.
Replicates in cytoplasm
3.
Single, stranded, Icosahedral nucleocapsid
4.
Acid and bile stable but no long term carrier
state
5.
Three serologic (antigenic) types based on different antigenic determinants on
the outer capsid protein
6.
Release upon death of the cell
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A child suffering from Poliomyelitis |
Disease caused by Polio virus:
Disease cause by polio virus is poliomyelitis
Pathogenesis of Poliomyelitis:
Transmission: faeco-oral route (by ingestion of contaminated food
and drink)
Host: Human
Incubation period: 7-14 days
Mechanism of pathogenesis:
1.
Polio virus enters into the body by faeco-oral
route
2.
Replicate in the lymphoid tissue of the
orophraynx and SI (Peyer’s patches)
3.
Spreads through blood stream to the CNS and also
spreads retrograde along nerve axons
4.
Then replicates in the motor neurons located in
the ant. Horn of the spinal cord
5.
Death of nerve cells
6.
Result: Paralysis of the muscle innervated by
those neurons. Also affects the brain stem, leading to bulbar poliomyelitis
(with respiratory paralysis) but rarely damage the cerebral cortex.
Prevention/ Prophylaxis / Vaccination against Polio virus:
1. Live attenuated (sabin/oral vaccine/ opv)
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Vaccination against Polio Virus |
Dose
|
Time
|
Time
|
1st
|
At birth
|
4th-14th weeks after birth
5th-9months of birth
|
2nd
|
6 weeks after birth
|
|
3rd
|
10 weeks after birth
|
2. Killed (salk/inactivated/IPV) vaccine:
·
At first 3 doses are given at intervals of 1-2
months
·
4th dose 6-12 months after that
Advantages of OPV (Oral Polio Vaccine):
1.
Cheaper, easy to administer
2.
Produce local gut immunity by provoking the production
of intestinal IgA
3.
Manufacture is easy
4.
Longer and strong immunity given
Disadvantages of OPV (Oral Polio Vaccine):
1.
It may revert back to virulent form
2.
Can also spread from vaccine to controls
3.
Cannot be given to pregnant women,
immunocompromised and aged person
4.
Presence of other virus may interfere with gut
colonization
5.
Multiple doses are necessary to establish
immunity
6.
Must be kept in refrigerator to prevent
heat-inactivation
Advantages of IPV (Inactivated Polio Vaccine):
1.
Dose not revert back to virulent form
2.
No reduction of potency due to interference
3.
Preservation is easy
4.
Less chance of contamination
5.
Can be given to pregnant women,
immunocompromised and aged person
Disadvantage of IPV (Inactivated Polio Vaccine):
1.
No local immunity
2.
Patient compliance is not good
3.
Large dose is required
4.
Expensive, shorter immunity
5.
More difficult to manufacture
That's all for today!
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