How Polio Develops

The three types of poliovirus belong to the virus family known as picornaviruses. This name derives from a combination of the words pico, meaning "small," and RNA, indicating that the viruses contain a core of the genetic material known as ribonucleic acid, or RNA.

Three types of poliovirus have been identified:

Type 1 (also known as Brunhilde)
Type 2 (Lansing)
Type 3 (Leon).

Type 1 is the most common form and the one most closely associated with polio’s more severe, paralytic progression. A person who develops immunity from exposure to one poliovirus type will not have immunity against the other polioviruses.

Poliovirus typically enters the body through the mouth and multiplies in the tonsils and lymph nodes of the upper respiratory tract. Infection proceeds from the mouth into the gastrointestinal tract through the stomach to the intestines. The virus multiplies in the intestines and is shed from the body in feces, often resulting in further infections.

For example, a parent can become infected by an infant during diaper changes, or improper waste disposal can lead to contamination of a water supply. These infections, in turn, will spread the virus more widely.

Large quantities of poliovirus multiply in intestinal tissue known as Peyer’s patches, where cells of the body’s lymphatic system are concentrated. Passage of the virus into the body’s lymphatic system stimulates the production of antibodies.

These specialized immune-system defenders, in time, will destroy the viral intruder. From the lymphatic system, the virus typically invades the bloodstream.