acute infectious disease of humans, particularly children, caused by any of three serotypes of human poliovirus; infection is usually limited to the gastrointestinal tract and nasopharynx, and is often asymptomatic; the central nervous system, primarily the spinal cord, may be affected, leading to rapidly progressive paralysis, coarse fasciculation and hyporeflexia; motor neurons are primarily affected and encephalitis may also occur; replicates in the nervous system, and may cause significant neuronal loss, most notably in the spinal cord.