A virus called poliovirus causes polio in humans. Poliovirus is transmitted through feces and can be passed on by contact with an infected person or contaminated food or water. The polio vaccine is the most effective way to prevent the illness.
Most people that are infected with poliovirus have no symptoms and are unaware of it. Some people develop nonparalytic polio, which causes mild flu-like symptoms. Rarely, paralytic polio results from infection with poliovirus, causing muscle aches and weakness and loss of reflexes. Another effect of poliovirus, known as post-polio syndrome, causes disabling symptoms many years after a person is infected. Common symptoms of post-polio syndrome include excessive fatigue, progressive muscle weakness and problems with memory, breathing or swallowing.