1% to 2% of poliovirus infections result in neurologic signs and symptoms; the rest are asymptomatic, or cause minor illness with symptoms such as fever, muscle aches, and gastrointestinal difficulties. The symptoms of more severe cases include high fever, headache, vomiting, and neck and back stiffness, followed by paralysis.

Paralytic polio can occur when the poliovirus invades motor neurons. In cases where paralysis results, the disease is referred to as acute paralytic poliomyelitis or APP. APP was fatal in 5 to 10 percent of cases; with better respiratory management, this rate is almost certainly lower now.

 

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