A 4-year-old unvaccinated child from rural West Bengal presents with a 2-week history of fever and malaise, followed by sudden onset of weakness in the right lower limb. On examination, the child has **asymmetric flaccid paralysis** (marked **A** in the diagram) with absent deep tendon reflexes in the affected limb and preserved sensation. Stool samples are sent for viral isolation. Which of the following is the most likely causative organism responsible for this clinical presentation?