Final answer:
Poliovirus most commonly affects the lumbar levels of the spinal cord, potentially leading to flaccid paralysis and respiratory involvement.
Step-by-step explanation:
The spinal cord level most commonly affected by poliovirus is the anterior horn cells in the lumbar levels of the spinal cord. Poliovirus invades and replicates in motor neurons, leading to cell destruction and potentially causing flaccid paralysis, which can be severe and involve the respiratory system. Damage to different levels of the spinal cord may result in varying forms of paralysis, such as quadriplegia or paraplegia, depending on whether the cervical, thoracic, lumbar, or sacral regions are affected.