Poliomyelitis commonly known as polio or infantile paralysis, is an infectious virus disease in the brain and spinal cord. It is usually spread through infected faecal matter entering the mouth or by ingesting food or water containing human faeces. The virus can within a few hours cause muscle weakness and subsequent paralysis. The disease most commonly attacks the legs, but may also involve the head, neck and diaphragm. Most people recover fully from polio, but in those with muscle weakness about 2-5% of the children and 15-30 % of the adults die. In up to 70 % of the infections there are no symptoms. Years after recovery, post-polio syndrome may occur, with a slow development of muscle weakness.