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Poliomyelitis is caused by the poliovirus, a non-enveloped RNA virus from the Picornaviridae family.

In young children, the virus enters the body through the fecal-oral route, typically by ingesting contaminated food or water.

Once inside, the virus replicates in the mucosal lining of the throat and intestines, remaining mostly asymptomatic.

In symptomatic cases, the virus then spreads to the lymph nodes and enters the bloodstream, causing primary viremia.

As the infection progresses, the virus reaches the central nervous system, particularly the spinal cord.

The virus may also reach the spinal cord through retrograde axonal transport from peripheral nerves.

There, it targets and replicates in the anterior horn of the spinal cord.

This results in the destruction of motor neurons that control muscle movement, leading to motor impairment.

This condition is known as paralytic poliomyelitis, and it is characterized by the sudden onset of asymmetric flaccid paralysis, often affecting the legs.