Fever, headache, and sometimes mild GI symptoms followed in 3-10 days by fever, severe myalgia, stiff neck, and asymmetric flaccid paralysis; [ID, p. 2044] 1/200 cases: irreversible paralysis; 5% to 10% of paralyzed children die; [WHO website]
Flaccid paralysis of the lower extremities develops quickly. It is usually asymmetrical and is associated with fever, stiff neck, myalgias, and headache. Patients have diminished deep tendon reflexes, but no loss of sensation. [ID, p. 2044] Early signs of bulbar palsies include "dysphagia, nasal regurgitation, and nasal voice." [Merck Manual, p. 1427] About 90% of infections are inapparent or nonspecific. About 10% of patients have flu-like symptoms including fever, headache, and nausea. Flaccid paralysis develops in less than 1% of cases. [CCDM, p. 477-84] The three main varieties of disease are spinal paralytic poliomyelitis (0.1% of all polio infections), bulbar paralytic poliomyelitis (5% to 35% of paralytic cases), and polioencephalitis (uncommon). Severe myalgias and sometimes paresthesias and fasciculations herald the onset of the major illness. The paralysis is usually asymmetrical. Reflexes are hyperactive initially, then absent. Bulbar disease may include dysphagia, pharyngeal paralysis, and dyspnea. Polioencephalitis is uncommon, occurs mainly in infants, and is associated with seizures. Guillain-Barre syndrome should be suspected if sensory loss (very rare in polio). [PPID, p. 2074-5] Because polio is an infection of the anterior horns of the spinal cord, sensation is normal. [Cecil, p. 2380]
In the differential diagnoses are other enteroviral infections, West Nile virus infection, and Guillain-Barre syndrome, the last of which differs in having symmetrical weakness, sensory loss in 70% of cases, CSF protein but normal cell count, and no fever. [Merck Manual, p. 1427] Other causes of acute flaccid paralysis are other viral infections, Guillain-Barre syndrome, acute motor axonal neuropathy, transverse myelitis, traumatic neuritis, infectious and toxic neuropathies, tick paralysis, myasthenia gravis, porphyria, botulism, insecticide poisoning, polymyositis, trichinosis, and periodic paralysis. [CCDM]
The Global Polio Eradication Initiative (GPEI) eliminated polio in the Americas with the last wild poliovirus case reported in 1991. GPEI has reduced the number of reported cases in the world by more than 99% since the mid-1980s. "As of April 2016, WPV [wild poliovirus] circulation has never been interrupted in only 2 countries: Afghanistan and Pakistan." OPV (live oral poliovirus vaccine) is no longer recommended for routine immunizations in the US. Unvaccinated adults travelling to areas where polio has not yet been eradicated should receive three doses of IPV. [CDC Travel, p. 278-82]
Spread by food or milk may occur, but it is rare. The disease is transmitted mainly by the fecal-oral route. [CCDM] "Enterovirus 71 and West Nile virus can cause an identical clinical illness." [Cecil, p. 2379]
For updated text and symptoms of infectious diseases, see iddx.com.