Epidemiology of Poliomyelitis Ashry Gad Mohamed MBchB, MPH, DrPH Prof. of Epidemiology Medical 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

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

Level Globally Endemic countries Non endemic countries

Country Pakistan89134 Afphanistan3823 Mauritania135 India74141 Chad6418 Nigeria38813 Congo375 Sudan45- Angola2930 Russia014

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 Communicability7-10 days before onset Virus present in stool 3-6 weeks

Poliovirus Vaccine 1955Inactivated vaccine 1961Types 1 and 2 monovalent OPV 1962Type 3 monovalent OPV 1963Trivalent OPV 1987Enhanced-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) Healthy recipients of OPV41% Healthy contacts of OPV recipients31% Community acquired 5% Immunodeficient24%

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 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

References polio.htm 4- Control of communicable diseases in man, manual. APHA 2005.