Polio is much more common amongst infants and younger children and occurs under the conditions of poor hygiene. The poliovirus is a type of a neurotropic virus, that is, it has an affinity to the nerves. It generally affects the portion of the spinal cord that contains the motor nerve tracts. This eventually leads to the paralysis of one set of the muscles of the body and causes the opposite set of the muscles to contract vigorously. This leads to the formation of the deformities that are seen in the people affected by polio.