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For further information, see CMDT Part 32-02: Major Vaccine-Preventable Viral Infections

Key Features

Essentials of Diagnosis

  • Incubation period 7–14 days after exposure

  • Headache, stiff neck, fever, vomiting, sore throat

  • Lower motor neuron lesion (flaccid paralysis) with decreased deep tendon reflexes and muscle wasting; sensation intact

General Considerations

  • Poliomyelitis virus, an enterovirus, is highly contagious through fecal-oral route, especially during the first week of infection

  • There are three wild poliovirus serotypes, however, only wild poliovirus type 1 has remained endemic since 2012

  • Pakistan, Afghanistan, and Nigeria remain the only countries with endemic poliovirus transmission since 2014

  • In 2019, there were 29 cases of wild type polio in Afghanistan and 146 in Pakistan

  • In 2020, there have been 2 cases of wild type polio in Afghanistan and 21 cases in Pakistan

  • In 2019, there were 354 vaccine-derived polio cases, derived mostly from type 2 attenuated live oral poliovirus vaccine (OPV), reported in 17 countries

  • In 2020, there have been 18 cases of vaccine-derived polio reported in 7 countries

  • Cases of acute flaccid myelitis (formerly acute flaccid paralysis) resembling polio but not due to poliomyelitis virus are being reported

Clinical Findings

Symptoms and Signs

  • At least 95% of infections are asymptomatic

  • Patients who become symptomatic can present with abortive poliomyelitis, nonparalytic poliomyelitis, or paralytic poliomyelitis

    • Abortive poliomyelitis: minor illness with nonspecific symptoms, fever, headache, vomiting, diarrhea, constipation, and sore throat lasting 2–3 days

    • Nonparalytic poliomyelitis: In addition to the above symptoms, signs of meningeal irritation and muscle spasm occur in the absence of frank paralysis

    • Paralytic poliomyelitis: present during the febrile period over 2–3 days, is a flaccid asymmetric paralysis affecting mostly the proximal muscles of the lower extremities

      • Sensory loss is very rare

      • Can be divided into two forms that may coexist: (1) spinal poliomyelitis, involving the muscles innervated by the spinal nerves; and (2) bulbar poliomyelitis, involving the muscles supplied by the cranial nerves (especially nerves IX and X) and of the respiratory and vasomotor centers

  • Post-polio syndrome

    • Constellation of symptoms that affect polio survivors and is not infectious

    • The syndrome presents with signs of chronic and new denervation

    • The most frequent symptoms are progressive muscle limbs paresis with muscle atrophy, with fasciculations and fibrillation during rest activity

  • Acute flaccid myelitis

    • There is no evidence of poliomyelitis infection

    • Enteroviruses are isolated in some of these cases

Differential Diagnosis

  • Acute inflammatory polyneuritis (Guillain-Barré syndrome)

  • Japanese encephalitis virus infection

  • West Nile virus infection

  • Tick paralysis

  • Acute flaccid myelitis


  • The virus may be recovered from throat washings (early) and stools (early and late)

  • PCR of washings, stool, or cerebrospinal fluid can also facilitate diagnosis

  • Cerebrospinal findings

    • Normal or slightly increased pressure and protein

    • Glucose is not decreased

    • White blood cells ...

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