On May 31, 2017, 58-year-old Tamela Wilson checked into Barnes-Jewish Hospital, in St. Louis, with a fever, fatigue, and a strange red rash. She’d been undergoing chemotherapy to treat a relapsing lymphoma, but this exhaustion wasn’t just the cancer or the drugs. She told the doctors she worked at nearby Meramec State Park, tending to its miles of trails through forested river bluffs. And that while there, a week before her symptoms started, she found two ticks burrowed into her body.

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