Review Question - QID 210681

A 14-year-old boy is brought to his pediatrician complaining of a fever he has had for several days. In addition, he says that he has been getting painful sores in his mouth. He is otherwise healthy though there is a family history of immunodeficiency. He reports that he walked through the woods and drank from a mountain stream on a school field trip a few days before he started developing symptoms. On presentation, his temperature is 101.1°F (38.4°C), blood pressure is 118/73 mmHg, pulse is 87/min, and respirations are 14/min. On physical exam, the boy appears fatigued. He is alert and able to follow instructions. A rash is seen that is shown in Figure A. Which of the following is most consistent with the cause of this patient's disease?