What causes polio?

Polio is caused by any one of three serotypes of poliovirus belonging to the genus Enterovirus and the family Picornaviridae. The viruses in this family are small in size and contain a single-stranded RNA genome. The polioviruses in particular consist of a single strand of twelve genes that target a host's nerve cells.

Polioviruses tend to inhabit the alimentary canal (the canal where food is taken in, passed through, and excreted). Polioviruses have only been found to inhabit the alimentary canals of humans, monkeys, and chimpanzees.

The enteroviruses are acid-resistant, which allows them to travel safely through the acidic stomach to where they can replicate in the small intestine. The viruses are transmitted easily through the fecal-oral route, and are shed for two to three weeks after the initial infection.

Therefore, polio is most prevalent in areas with poor hygienic standards, and the virus can survive for several weeks in water and sewage.

Because there are three immunologically unrelated serotypes of poliovirus, antibody production against one of the three serotypes does not protect against the other serotypes. However, there can be some cross-protection between serotypes 1 and 2.