A 9-year-old boy from the northeastern United States presents with a 10-day history of an expanding rash on his left thigh following a tick bite while camping. On examination, the lesion shows the characteristic pattern marked **D** in the diagram — a central area of erythema with partial clearing and an expanding outer red ring. The child is afebrile and denies pain or itching at the site. Which of the following is the most appropriate next step in management?