Polio is transmitted by:

1. Natural infection occurs only in humans. Infected humans excreting poliovirus in their stool are the major reservoir of infection. Infected stool containing poliovirus is the major source. The viruses secreted in throat secretions during early stage of the illness may also be another source of infection. The poliovirus is transmitted: Primarily by the fecal-oral route by ingestion of food and water contaminated with human feces. By inhalation or through fomites contaminated with respiratory secretions. 2. Poor sanitation, low socioeconomic status, and crowded living conditions facilitate transmission of infection.