Polio - Causes

Poliovirus is transmitted through saliva and feces. It is passed on when people do not wash their hands after eating or using the bathroom. Once a person is infected with the virus, it can remain in the mouth and throat for about three weeks. It then travels to the intestine. It can remain in the intestine for up to eight weeks.

Inside the intestine, the virus multiplies rapidly. It may invade the lymphatic (pronounced lim-FAT-ic) system. The lymphatic system consists of organs and tissues that help protect a person against disease. The virus eventually enters the bloodstream. It can then pass to the central nervous system (the brain and spinal cord). The virus can also pass directly into nerves. It can then travel along a nerve to the brain.