Poliomylitis

POLIOMYELITIS

Epidemiology, Prevention & Control

Introduction

A viral infection most often recognized by acute onset of flaccid paralysis. Infection with poliovirus results in a spectrum of clinical manifestations from inapparent infection to non-specific febrile illness, aseptic meningitis, paralytic disease, and death.

Poliovirus

Genus: Enterovirus 3 serotypes type 1, 2 & 3 All types can cause paralysis Type 1 most frequently causes epidemics Most vaccine-associated cases are due to type 2 or 3

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


Left: Picture of poliovirus. The poliovirus is extremely small, about 50 nm (nanometer = one-billionth of a meter) Courtesy of David Belnap and James Hogle
Right: Cross-section of the poliovirus showing the RNA, capsid, and nerve cell receptors Illustration courtesy of Link Studio

Case definition

The following case definition for paralytic poliomyelitis has been approved by CDC (1997) Clinical case definition Acute onset of a flaccid paralysis of one or more limbs with decreased or absent tendon reflexes in the affected limbs, without other apparent cause, and without sensory or cognitive loss.



Clinical case definition of WHO Any child under 15 years of age with acute flaccid paralysis (AFP)* or any person of any age with paralytic illness if polio is suspected ...


Two phases of acute poliomyelitis can be distinguished: a non-specific febrile illness including: fever, malaise, headache, nausea & vomiting (minor illness) followed, in a small proportion of patients, by aseptic meningitis and/or paralytic disease (major illness).

Flaccid paralysis occurs in less than 1% of poliovirus infection; over 90% of infections are either inapparent or result of nonspecific infection. The paralysis of polio is usually asymmetric & the maximum extent is reached in a short period (3-4 days).

Outcomes of poliovirus infection

Epidemiology of polio
Reservoir: Human…Incubation period: 7-14 days for paralytic cases…Period of communicability: not precisely defined,, in throat secretion 36 hours & in feces 72 hours after exposure to infection.

Epidemiological pattern

The epidemiological pattern of polio depends upon the degree of the socioeconomic development and health care services of a country. The pattern of the disease has been considerably modified by widespread immunization.

Mode of transmission

Since foci of infection are the throat and small intestines, poliomyelitis spreads by two routes:Fecal-oral infection…Oral-oral infection: direct droplet infection .. Where sanitation are high… pharyngeal spread may be more important !! In rare cases, Food-borne (ingestion) infection through the ingestion of contaminated foods. Vehicles include milk, water, or any others that may be contaminated by handling, flies, dust….

Diagnosis

Definitive laboratory diagnosis required isolation of the wild poliovirus from stool samples, CSF or oropharyngeal secretions in cell culture system of human or monkey origin (primate cells).

Prevention

General prevention: Health promotion through environmental sanitation. Health education (modes of spread, protective value of vaccination).

Prevention … Active immunization: Salk vaccine (intramuscular polio trivalent killed vaccine). Sabin vaccine (oral polio trivalent live attenuated vaccine).

Inactivated Polio Vaccine

Contains 3 serotypes of vaccine virus Grown on monkey kidney (Vero) cells Inactivated with formaldehyde

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 life-long

Polio Vaccination Schedule

Age 2 months 4 months 6-18 months 4-6 years

Salk versus Sabin vaccine

IPV (Salk)
OPV (Sabin)
killed formolised virus Given SC or IM Induces circulating antibodies, but not local (intestinal immunity) Prevents paralysis but does not prevent reinfection Not useful in controlling epidemics More difficult to manufacture and is relatively costly
live attenuated virus given orally immunity is both humoral and intestinal. induces antibody quickly Prevents paralysis and prevents reinfection Can be effectively used in controlling epidemics. Easy to manufacture and is cheaper

Polio Vaccine Adverse Reactions

Rare local reactions (IPV) No serious reactions to IPV have been documented Paralytic poliomyelitis (OPV)

Polio VaccineContraindications and Precautions

Serious allergic reaction to component or following prior dose Moderate or severe acute illness

Polio Eradication

Last case in United States in 1979 Western Hemisphere certified polio free in 1994 Last isolate of type 2 poliovirus in India in October 1999 Global eradication goal by 2005



In Iraq… The last laboratory-confirmed indigenous polio case was reported on 28 January, 2000. In 2014 two wild polio cases were reported from Baghdad – Resafa province. Dates of onset of the cases were February and April 2014. Both cases were linked to Syria outbreak of 2013.

Wild Poliovirus 1988

Wild Poliovirus 2000

Control of patients and contacts

Report to local health authority..Isolation: Enteric precautions in the hospital for wild virus disease.Concurrent disinfection: throat discharges, feces and articles…

Protection of contacts: Immunization of familial and other close contacts is recommended. Investigation of contacts and source of infection: Occurrence of a single case of poliomyelitis due to wild infection must be recognized as a public health emergency promoting immediate investigation.

Epidemic measures:

In any country, a single case of poliomyelitis must now be considered a public health emergency, requiring an extensive supplementary immunization response over a large geographic area.

Disaster implications:

Overcrowding of non-immune groups and collapse of the sanitary infrastructure pose an epidemic threat.
Pigmentation

E. International measures:

Poliomyelitis is a Disease under surveillance by WHO and is targeted for eradication by 2005. National health administrations are expected to inform WHO immediately of individual cases and to supplement these reports as soon as possible with details of the nature and extent of virus transmission. Planning a large-scale immunization response must begin immediately and, if epidemiologically appropriate, in coordination with bordering countries.

E. International measures (cont.):

Once a wild poliovirus is isolated, molecular epidemiology can often help trace the source. Countries should submit monthly reports on acute flaccid paralysis (AFP) cases and AFP surveillance performance to their respective WHO offices. International travelers visiting areas of high prevalence must be adequately immunized.

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