Virology USMLE Step 1 Practice Question

A 7-year-old boy presents to the clinic with a 3-day history of high fever (39.8°C), severe oral pain, and progressive dysphagia. His mother reports he attended summer camp 5 days ago. Vital signs show HR 115/min, RR 24/min, and BP 105/68 mmHg. Physical examination reveals shallow ulcers distributed on the buccal mucosa, tongue, and hard palate with surrounding erythema. Additionally, a vesicular rash is noted on the palms and soles. There is no pharyngeal exudate, cervical lymphadenopathy, or hepatosplenomegaly. Laboratory studies show WBC 11,200/µL, CRP 8.2 mg/dL, and normal liver function tests. Which of the following is the most likely causative agent?