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Transmission is through faecal-oral spread.
The infection may be clinically unapparent. If symptoms occur, they may include headache, gastro-intestinal disturbance, malaise and stiffness of the neck and back, with or without paralysis. Asceptic meningitis may also occur. The proportion of unapparent to paralytic infections may be as high as 1,000 to 1 in children and 75 to 1 in adults, depending on the poliomyelitis virus type and social and environmental conditions. The incubation period ranges from 3-21 days.