An 11-year-old boy presents with a 3-day history of high fever, severe headache, and myalgias. He reports no rash. His symptoms resolved completely, but he returns to the clinic 6 days later with an identical recurrence of high fever. The family went on a camping trip in the mountains of Colorado two weeks ago. What is the most likely finding on a Wright-stained peripheral blood smear obtained during a febrile episode?