The ability of poliovirus to invade the CNS is facilitated by which transport mechanism?

• A. Anterograde axonal transport
• B. Retrograde axonal transport
• C. Passive diffusion across meninges
• D. Trans-synaptic migration only

Answer: (B)

Poliovirus reaches the CNS by traveling retrogradely along peripheral motor neurons. After initial infection at peripheral sites such as the neuromuscular junction, the virus is taken up by the nerve terminal and hijacks the neuron’s transport machinery to move toward the neuron's cell body in the spinal cord and brainstem. This retrograde axonal transport uses dynein motors and microtubules, delivering the virus to motor neurons in the CNS where it can cause damage and paralysis. Anterograde transport would move material away from the CNS, passive diffusion across the meninges isn’t a plausible route for this virus, and while some spread can occur across synapses, the established mechanism initiating CNS entry is retrograde axonal transport.