Transcript - Department of Community Medicine ACME Pariyaram

POLIOMYELITIS
AGENT FACTORS:
Agent: Poliovirus,
- RNA virus, serotype –1,2,3
- Most outbreaks – type 1
-Survive for long periods in external
environment in cold climate
- Can live in water for 4 mnths &
faeces for 6 mnths
- hence faecal – oral route
Reservoir of infection:
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Man is the only known reservoir
Most are subclinical cases, no chronic
carrier, no animal carriers
Mild & subclinical cases plays an
important role in spread of infection
Submerged part in iceberg phenomenon
For every clinical case- 1000 children and
75 adult subclinical cases
Infectious material:
•
Faeces and Oro-pharyngeal secretions of
an infected person
Period of communicability:
Cases are most infectious 7 to 10 days
before and after onset of symptoms
• In faeces the virus is excreted for 2 to 3
wks & can go on for as long as 3 – 4 mnth
•
HOST FACTORS:
Age:
 occur in all age groups
 Children are more susceptible than adults
 Most vulnerable age is between 6 months
to 3 years in India
Sex: M:F, 3:1
Risk factors:
Paralytic polio in an individual who have
been already infected with polio virus, has
been found to precipitated by factors like -

fatigue, trauma, intra muscular injections,
operative procedures esp. during
epidemics of polio, immunizing agents
particularly alum containing DPT
Immunity:
• Infection with one type does not offer
complete protection against other two type of
viruses
• Neutralizing Ab’s - index of immunity to polio
after infection
Environmental factors:
• More seen to occur in rainy season
• Sources are contaminated water, food, flies
• Overcrowding and poor sanitation provides
opportunities for exposure to infection
Mode of transmission:
• Faecal-oral route – developing countries
• Droplet infection – developed countries,
acute phase of disease
Incubation period: 7-14 days(range 3-35
days)
Clinical spectrum:
a) Inapparent (subclinical) infection
b) Abortive polio or minor illness
c) Non paralytic polio
d) Paralytic polio
a) Inapparent (subclinical) infection:
Occurs in approx. 91-96% infections
• No symptoms
• Recognized only by virus isolation or rising
antibody titres
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b) Abortive polio or minor illness:
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Occurs in 4-8% of infections
Causes only mild or self limiting illness
Patient recovers quickly
Recognized only by virus isolation or rising
antibody titres
c) Non paralytic polio:
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Occurs in 1% of all cases
s/o: stiffness and pain in neck and back
Disease lasts 2 to 10 days
Recovery is rapid
It is synonymous to aseptic meningitis
d) Paralytic polio:
• Occurs in less than 1% cases
• Invades CNS & causes paralysis of varying
degree
• Predominant sign – Asymmetrical flaccid
paralysis (AFP)
• If fever at time of onset of paralysis –
polio suspected
• Other symptoms - malaise, anorexia,
nausea, vomiting, abdominal pain, sore
throat, head ache and constipation
 Signs:
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stiffness of neck & back muscles
Tripod sign
Descending paralysis – hip to downwards
Asymmetrical patchy paralysis
DTRs are diminished before onset of
paralysis
Progression of paralysis to reach its
maximum in majority cases occurs in less
than 4 days
No sign of sensory loss
Cranial nerve involvement seen in bulbar and
bulbo spinal forms of paralytic polio
• Facial asymmetry, difficulty in swallowing,
weakness of voice
• Respiratory insufficiency can be life threatening &
is usually cause of death
• Atrophy of muscles also seen
• Progressive paralysis, coma & convulsions
indicate diagnosis other than polio
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Treatment:
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No specific treatment
Physiotherapy and good nursing care from
beginning can minimize/ prevent crippling
Prevention:
Immunization is the most effective
method
• Two types of vaccine:
•
a)
Inactivated polio vaccine(IPV)/ Salk
b)
Oral polio vaccine(OPV)/ Sabin
Inactivated polio vaccine(IPV)/ Salk:
• Given i/m (preferred) or s/c injection
• Stable at ambient temperature, but
should be refrigerated to ensure no loss of
potency
• Freezing should be avoided
• Primary course of immunization consist of
4 inoculations
• Available as stand alone product or in
combination form
• Induces humoral antibody and not
intestinal/ local immunity
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IPV protect individual from paralytic polio, but do
not prevent re-infection of gut by wild polio
viruses
Hence it does not offer any benefit for the
community as wild virus can multiply in gut and
be a source of infection to others
It is unsuitable during epidemic because:
a)
Immunity is not rapidly achieved, more than
one dose required to induce immunity
b)
Injections are to be avoided during epidemics
as they may precipitate paralysis
Advantages:
• Can be given in immuno compromised
and pregnant women
Associated risks:
• No serious ADRs except minor local
erythema, induration and tenderness
Oral polio vaccine(OPV)/ Sabin:
Described by Albert Sabin in 1957
 Contains live attenuated vaccine (type 1,2,3)
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National immunization schedule:
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Primary course of 3 doses at 1 month interval
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Starting at 6 wks and followed by 10 & 14 wks
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Zero dose is recommended at birth
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All infants should vaccination before 6 months of age as most
polio cases occur between 6 months to 3 years period
1
1
 One booster dose of OPV is given at 2 yrs
Dose & mode: 2 drops, orally
Development of immunity:
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IgA produced in intestine prevent subsequent
infection of alimentary canal with wild polio, thus
preventing spread in community
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OPV induces both local & systemic immunity
Vaccine progeny excreted in faeces
2* spread to
household contact & susceptible host in community
Herd immunity established
• This property eliminates wild polio from the
community & replace it with attenuated strain
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Advantages:
1.
2.
3.
4.
5.
6.
7.
Easy to administer
Doesn't require highly trained personnel
Induce both humoral and intestinal
immunity
Even single dose elicits substantial
immunity
Herd immunity
Useful in controlling epidemics
Relatively inexpensive
Complications:
• VAPP(vaccine associated paralytic
poliomyelitis)----due to type 3 strain
Containdications:
• All live vaccines are C/I in immuno
compromised patients and pregnant
women
• IPV given in immuno compromised if
necessary
Storage:
A) stabilized vaccine – recent vaccines are
heat stabilized by adding magnesium
chloride in it
 Can be kept for a year at 4* C & for a
month at 25*C with out loosing potency
B) Non stabilized vaccine – Vaccine sould
be stored at -25*C in deep freezer
 Vaccine vial kept in ice at field level during
administration to children
Sequential administration of IPV & OPV:
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In some countries sequential schedule of
1 – 2 dose of IPV followed by > 2 doses of
OPV has been adopted
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This approach reduce the event or even
prevent VAPP, while giving both systemic
and local immunity
Differences
between IPV & OPV
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2.
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4.
IPV(Salk)
Killed virus
Given s/c or i/m
Only humoral
immunity, no local
immunity
More difficult to
manufacture
1.
2.
3.
4.
OPV(Sabin)
Live attenuated
Orally
Both humoral &
intestinal
immunity
Easy to
manufacture
IPV
Prevent paralysis, but
do not prevent reinfection with wild
polio
6. Not useful in
epidemics
7. Virus content is
10,000 times more
than OPV, Costlier
8. Doesn't require
stringent condition
during storage &
transportation
5.
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OPV
Prevent paralysis and
also intestinal reinfection
Can be used in
epidemics
Cheaper
Required to be stored
& transported in sub
zero temperature
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