Over the past 40 years, Dr. Timothy Lepore has been the emergency room head, sole surgeon and medical examiner on Nantucket, a small island off Cape Cod, Massachusetts. Today he runs the only private practice, where he treats dozens of patients with Lyme disease each year. About 15% of residents on the island have been afflicted with the disease, which can cause a wide range of symptoms like a fever, rash, facial paralysis, an irregular heartbeat and arthritis.