Caused by a single-stranded RNA enterovirus transmitted by the fecal-oral route.

Humans are the only known reservoir of the virus.

The virus causes a transient Infection without paralysis.

Poliovirus primarily infects the intestinal tract, and is symptomatic in only about 25% of cases, typically causing a flu like illness.

Depending on the virus type, 1 to 5% of patients with infections will develop meningitis.

About 0.5 to 0.05% of those who are infected, that is one in 200 to one in 2000 individuals will develop paralysis after the virus infects the spinal cord, and a small proportion of them will die as a result of respiratory failure.

Occurs when one of three poliovirus types infects the anterior horn cells of the spinal cord resulting in flaccid paralysis, respiratory failure, and potentially death.

Among infected patients, poliovirus may be recovered from stool, throat, and in rare instances from the spinal fluid.

In older children, adolescents, and adults these infections can result in severe paralysis they can leave the patient dependent on artificial support for ventilation.

Patients paralyzed from polio may eventually recover, but May suffer complications over a lifetime.

The US incidence of polio peaked in the 1950s at 20,000 cases per year. 

The last known case in the United States occurred in 1979.

Universal vaccination with the trivalent, inactivated injected form of polio vaccine of all infants is recommended, with three doses of vaccine given a two, four, and 12 – 15 months of age, and a booster at four – six years of age.

Excretion of the virus in infected patients is intermittent.

223 cases were reported worldwide in 2012, with the disease largely restricted to a few regions of Nigeria, Pakistan, and Afghanistan.

Serologic tests may support the diagnosis but are not confirmatory.

Within the Picornaviridae family.

These viruses are resistant to ether and chloroform.

Inactivated by formaldehyde.

They multiply in the GI tract.

Are neurotropic.

Paralysis develops in fewer than 1 in 100 infected persons.

Clinical syndrome of fever with asymmetrical flaccid weakness that usually affects the lower extremities.

Can manifest in 4 different forms: inapparent infection, abortive disease, nonparalytic poliomyelitis, and paralytic disease.

Prevalence has decreased significantly since then because of aggressive immunization programs.

Transmitted through the oral-fecal route or by ingestion of contaminated water.

Three serotypes cause human infection.

Incubation period is 5-35 days.

Viral particles initially replicate in the nasopharynx and GI tract and then invade lymphoid tissues, with subsequent hematologic spread.

Following viremia, the virus becomes neurotropic and produces destruction of the motor neurons in the anterior horn and brainstem.

The destruction of motor neurons leads to the development of flaccid paralysis, which may be bulbar or spinal in distribution.

No cases of wild-type poliovirus infection have been reported in the United States since 1979.

The last case of paralytic poliomyelitis caused by serotype 2 wild polio virus was detected in 1999.

The number of new polio cases caused by the two remaining wild serotypes has decreased by 99% between 1988 and 2005.

Since January 2010 new polio cases have decreased by 95% in the worlds largest remaining reservoirs of indigenous virus in northern India and northern Nigeria.

A few cases reported with the use of vaccine are reported annually, but the number has fallen with the institution of all-inactivated poliovirus vaccine.

Global incidence of poliovirus infection has decreased by more than 99% since 1988.

Wild-type virus infections persist in very few countries, an no deaths due to wild-type poliovirus have been reported in the United States since 1979.

Mortality may be associated with cases of paralytic poliomyelitis and is associated with complications such as respiratory failure.

90-95% of cases are not apparent, while 5-10% of patients with the infection have symptoms.

Affects both sexes equally and is primarily a disease of children, but susceptible inividulas of any age can be infected.

5-10% of cases are abortive and patients experience anorexia, nausea, vomiting, abdominal pain for 5 days or less, and have a normal neurologic examination.

Nonparalytic poliomyelitis is associated with symptoms as above with the addition of meningeal irritation.

Paralytic poiliomyelitis associated with respiratory failure in addition to the protean symtpoms noted previously.

Postpoliomyelitis syndrome can be seen in patients who recover from poliomyelitis and have recurrent weakness, fatigue and involvement of muscles groups previously affected.

Postpoliomyelitis can occur 20-40 yeas after the initial infection.

Illness presentation from asymptomatic to nonspecific symptoms of fever, headache, nausea, vomiting, abdominal pain, sore throat, neck rigidity, back pain, lower extremity pain, meningeal inflammation.

Fewer than 5% of patients have paralytic poliomyelitis with impaired motor neurons,which may be localized or widespread.

Paralytic poliomyelitis associated with asymmetric loss of muscle function in the major muscle groups and subsequently secondary muscle atrophy.

Paralytic poliomyelitis subject to complete, partial or no recovery.

Immunocompromised patients with HIV, B-cell lymphomas, and IgA deficient individuals are at high risk for acquisition of wild-type poliovirus and vaccine attenuated oral poliovirus vaccine.

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