Which of the following statements best describes the effect of poliovirus on the nervous system?

• A. It can lead to paralysis and loss of motor control
• B. It has no effect on the nervous system
• C. It only causes fever with no neurological involvement
• D. It primarily affects the immune system

Answer: (A)

Poliovirus is neurotropic and can invade the central nervous system, where it preferentially infects motor neurons in the anterior horn of the spinal cord and motor nuclei in the brainstem. Destruction of these neurons produces acute flaccid paralysis, with weakness and loss of motor control, often with reduced or absent reflexes. Sensation is typically spared, which helps distinguish this neuropathic paralysis from other conditions. While many infections are mild or asymptomatic, the hallmark nervous system effect when the virus reaches the CNS is paralysis due to motor neuron damage. The other statements don’t fit because the virus can affect the nervous system, neurological involvement can occur, and the primary issue is motor neuron destruction rather than solely an immune-system effect.