Poliomyelitis (polio) is caused by a virus that enters the body through the mouth mainly by fecal-oral contamination. Polio infections are more common in children less than five years of age; however, any person who is not immune to poliovirus, regardless of age, can become infected. Polio is most often recognized by the sudden onset of muscle paralysis but the majority of infected persons do not look or feel sick. Approximately, 0.1% to 1% of infections lead to irreversible paralysis, and amongst those paralyzed, 5%-10% die when the muscles that facilitate breathing become paralyzed. Because less than 1% of polio infections ever result in paralysis, poliovirus can spread widely before an outbreak is detected. There is no cure for polio but it can be prevented through immunization.
Source: Public Health Agency of Canada