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
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
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 • Destructionof 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: • high infant immunization coverage with four doses of oral poliovirus vaccine (OPV) in the first year of life; • supplementary doses of OPV to all children under five years of age during SIAs; • surveillance for wild poliovirus through reporting and laboratory testing of all acute flaccid paralysis (AFP) cases among children under fifteen years of age; • 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: • there are at least three years of zero polio cases due to wild poliovirus; • disease surveillance efforts in countries meet international standards; and • 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: • Completeness of reporting (80% at least). • Sensitivity of surveillance (1/100,000). • Completeness of case investigation (80% adequate stool specimen). • Complete follow up (80% 60 days). • 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 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.