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Epidemiology of Poliomyelitis
Ashry Gad Mohamed
MBchB, MPH, DrPH
Prof. of Epidemiology
Medical College, KSU
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First described by Michael Underwood in 1789
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Spectrum
Polio = grey & Myelitis =marrow (spinal cord)
& Itis = inflamation
95% asymptomatic.
4-8% minor non-specific illness (URTI, GIT,
influenza like)
1-2% Non paralytic aseptic meningitis.
1% Flaccid paralysis
Outcomes of poliovirus infection
Asymptomatic
Aseptic menigitis
0
20
Minor non-CNS illness
Paralytic
40
60
Percent
80
100
Flaccid paralysis
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Asymmetrical.
Affect large muscles.
No sensory loss.
No changes in recognation.
80% spinal, 19% bulbospinal & 1-2% bulbar
Mortality:
2-5% children
15-30% adults
25-75% bulbar type
Polio Eradication
• Before 1979 whole world
• Last case in United States in 1979
• Western Hemisphere certified polio
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free in 1994
1988
350.000
2001
483
2003
784
2006
1999
2007
673
Level
2009
2010
Globally
1606
874
Endemic countries
1256
211
Non endemic
countries
350
663
Country
2009
2010
Pakistan
89
134
Afphanistan
38
23
Mauritania
13
5
India
741
41
Chad
64
18
Nigeria
388
13
Congo
3
75
Sudan
45
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Angola
29
30
Russia
0
14
Wild Poliovirus 1988
Poliomyelitis 2004
Poliovirus
• Enterovirus (RNA)
• Three serotypes: 1, 2, 3
• Minimal heterotypic immunity
between serotypes
• Rapidly inactivated by heat,
formaldehyde, chlorine, ultraviolet light
Poliomyelitis Pathogenesis
• Entry into mouth
• Replication in pharynx, GI tract,
local lymphatics
• Hematologic spread to lymphatics
and central nervous system
• Viral spread along nerve fibers
• Destruction of motor neurons
Poliovirus Epidemiology
• Reservoir
Human
• Transmission
Fecal-oral
Oral-oral possible
• Communicability
7-10 days before onset
Virus present in stool
3-6 weeks
Poliovirus Vaccine
• 1955 Inactivated vaccine
• 1961
Types 1 and 2 monovalent OPV
• 1962
Type 3 monovalent OPV
• 1963 Trivalent OPV
• 1987
Enhanced-potency IPV (IPV)
Inactivated Polio Vaccine
• Contains 3 serotypes of vaccine virus
• Grown on monkey kidney (Vero) cells
• Inactivated with formaldehyde
• Contains 2-phenoxyethanol,
neomycin, streptomycin, polymyxin B
Oral Polio Vaccine
• Contains 3 serotypes of vaccine virus
• Grown on monkey kidney (Vero) cells
• Contains neomycin and streptomycin
• Shed in stool for up to 6 weeks
following vaccination
Inactivated Polio Vaccine
• Highly effective in producing
immunity to poliovirus
• >90% immune after 2 doses
• >99% immune after 3 doses
• Duration of immunity not
known with certainty
Oral Polio Vaccine
• Highly effective in producing
immunity to poliovirus
• 50% immune after 1 dose
• >95% immune after 3 doses
• Immunity probably lifelong
Polio Vaccine Adverse Reactions
• Rare local reactions (IPV)
• Vaccine associated paralytic
poliomyelitis (OPV)
Vaccine-Associated Paralytic Polio
• Increased risk in persons >18 years
• Increased risk in persons with
immunodeficiency
• No procedure available for identifying
persons at risk of paralytic disease
• 5-10 cases per year with exclusive use
of OPV
• Most cases in healthy children and their
household contacts
Vaccine-Associated Paralytic
Polio (VAPP) 1980-1998
• Healthy recipients of OPV
• Healthy contacts of
OPV recipients
• Community acquired
• Immunodeficient
41%
31%
5%
24%
Polio Vaccine
Contraindications and Precautions
• Severe allergic reaction to a
vaccine component or following a
prior dose of vaccine
• Moderate or severe acute illness
Global Polio Eradication Initiative
Objectives:
1-To interrupt transmission of the wild
poliovirus ASAP.
2-To achieve certification of global polio
eradication.
3-To contribute to health systems development
and strengthening routine immunization and
surveillance for communicable diseases in a
systematic way.
Global Polio Eradication Initiative
Strategies:
1.
high infant immunization coverage with four
doses of oral poliovirus vaccine (OPV) in the first
year of life;
2.
supplementary doses of OPV to all children under
five years of age during SIAs;
3.
surveillance for wild poliovirus through reporting
and laboratory testing of all acute flaccid paralysis
(AFP) cases among children under fifteen years of
age;
4.
targeted “mop-up” campaigns once wild
poliovirus transmission is limited to a specific
focal area
Global Polio Eradication Initiative
Before a WHO region can be certified polio-free,
three conditions must be satisfied:
1. there are at least three years of zero polio
cases due to wild poliovirus;
2. disease surveillance efforts in countries meet
international standards; and
3. each country must illustrate the capacity to
detect, report and respond to “imported”
polio cases
Poliomyelitis surveillance
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Acute flaccid paralysis
All cases of acute flaccid pralysis among
children younger than 15 years and all cases of
suspected polio in any person at any age.
• Performance indicators:
1. Completeness of reporting (80% at least).
2. Sensitivity of surveillance (1/100,000).
3. Completeness of case investigation (80%
adequate stool specimen).
4. Complete follow up (80% 60 days).
5. Lab investigation of all cases in WHO ref. lab.
The most important aspect of this classification is the
collection of 2 adequate stool samples from all cases.
Samples are considered adequate if both the
specimens (1) are collected within 14 days of
paralysis onset and at least 24 hours apart; (2) are of
adequate volume (8-10g) and (3) arrives at a WHOaccredited laboratory in good condition (ie, no
desiccation, no leakage), with adequate
documentation and evidence of cold-chain
maintenance
References
1-http://www.emro.who.int/PolioFax/
2-http://www.who.int/topics/poliomyelitis/en/
3-http://healthcare.utah.edu/healthinfo/adult/infectious/
polio.htm
4- Control of communicable diseases in man, manual. APHA
2005.