Polio is caused by a human enterovirus called the poliovirus. Wild polioviruses are those that occur naturally. The poliovirus consists of an RNA genome enclosed in a protein shell called a capsid. There are three serotypes of wild poliovirus – type 1, type 2, and type 3 – each with a slightly different capsid protein.
Type 2 poliovirus has been eliminated in the wild – the last wild type 2 poliovirus was detected in India in 1999. In this final stage of polio eradication, only type 1 and type 3 wild poliovirus continue to circulate in endemic areas. Both are highly infectious and both cause paralytic polio. Type 1 is the most pervasive strain of poliovirus and type 3 is at very low levels.
The Global Polio Eradication Initiative © Copyright 2010