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.