Poliovirus is highly communicable. The time between infection and onset of paralysis (incubation period) is 10–21 days (range 4–35 days). Transmission is primarily person to person via the faecaloral route, i.e. the poliovirus multiplies in the intestines and is spread through the faeces. The virus is intermittently excreted to one month or more after infection. Communicability of infected children is highest just prior to the onset of paralysis and during the first two weeks after paralysis occurs. The virus spreads rapidly and transmission is usually widespread by the time of paralysis onset. There is no long term carrier state in normal children.