A 3-year-old boy is brought to the physician for a 1-day history of fever and mouth sores. He has a 12-month history of similar episodes lasting 3 to 5 days that occur every 3 weeks. Temperature is 38.5 C. Physical examination shows various aphthous ulcers within the oral cavity. Laboratory studies show:
Hemoglobin 14 g/dL
Leukocytes 4000/μL
Neutrophils 5%
Lymphocytes 85%
Monocytes 10%
Platelets 300,000/μL
Which of the following is most likely responsible for this patient’s presentation?
