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Epidemiology of Poliomyelitis
Ashry Gad MohamedMBchB, MPH, DrPH
Prof. of EpidemiologyMedical College, KSU
• First described by Michael Underwood in 1789
• Polio = grey & Myelitis =marrow (spinal cord) & Itis = inflamation
• Spectrum
95% asymptomatic.
4-8% minor non-specific illness (URTI, GIT, influenza like)
1-2% Non paralytic aseptic meningitis.
1% Flaccid paralysis
0 20 40 60 80 100
Percent
Asymptomatic Minor non-CNS illness
Aseptic menigitis Paralytic
Outcomes of poliovirus infection
Flaccid paralysis
• 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 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 -
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 41%
• Healthy contacts of OPV recipients 31%
• Community acquired 5%
• Immunodeficient 24%
Polio VaccineContraindications 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
• 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 WHO-accredited laboratory in good condition (ie, no desiccation, no leakage), with adequate documentation and evidence of cold-chain maintenance
References1-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.