A 34 year-old geologist who works with an oil-exploration team in Central America comes to your clinic three weeks after returning from a trip to a dry, prairie-dog rich part of Central America. He remembers removing a tick from his leg four days before his departure from Central America, and having his first shaking chill on the plane home. He soon had a series of shaking chills, followed by fever for four days, and before he could get medical care, the fever and chills spontaneously resolved (went away) only to return for four days, then disappear again. His physical exam reveals no rash or organomegaly (enlarged organs such as liver or spleen), but he has a temperature of 104.8o F. As part of the patient's work up, you order a complete blood count. The technician doing the count calls you because there is a long curvaceous bacterium among the red blood cells on the smear of your patient's blood. The most likely cause of your patient's fever is: A. Treponema pertinue, causing "yaws" B. Borrelia recurrentis causing "relapsing fever" C. Treponema pallidum causing secondary syphilis D. Treponema carateum causing "Pinta"