A 75-year-old woman was seen at a local hospital with a chief complaint of febrile illness and myalgia. She had a heart rate of 145 bpm and a systolic blood pressure of 140 mmHg (Figure 1). Past medical history was unremarkable. She reported no known drug allergies and no current medications. There was no recent travel history. She reported no known tick bites. No unusual dietary exposure was noted. Within 30 minutes of admission, she complained of muscle cramps and had clammy skin and diarrhea. She appeared dehydrated and was started on saline intravenously for clinical dehydration and diagnosed with a likely viral illness and possible sepsis. A urinalysis revealed 3+ leukocyte esterase, 2+ protein, 95 white blood cells/hpf, and many bacteria. A comprehensive metabolic panel showed elevated renal (urea nitrogen = 10.5 mmol/L, creatinine = 114.9 mumol/L) and liver enzymes (AST = 114 U/L, ALT = 163 U/L), high glucose (8.56 mmol/L), and normal electrolytes. The patient was nonreactive for Hepatitis A IgM, Hepatitis B core IgM and surface IgG antibodies, and Hepatitis B surface antigen and HIV. A baseline troponin I was 0.03 mug/L. A complete blood count showed white blood cells (WBC) of 10.0 x 109/L and a hematocrit of 0.404. She was thrombocytopenic with a platelet count of 92 x 109/L. Microscopic examination of the peripheral blood smear revealed numerous loosely-coiled spirochetes consistent with Borrelia sp. infection (Figure 2). A working diagnosis of tick-borne relapsing fever (TBRF) was made. The patient was started on pantoprazole, levofloxin, and acetaminophen. Within 4 hours of antibiotic administration there was a clinical worsening of symptoms complicated by Jarisch-Herxheimer reaction (J-HR). The patient's temperature, blood pressure, and platelet count decreased rapidly (Figure 1). A urine culture was positive for E. coli, and antimicrobial therapy was changed to ertapenem and ciprofloxin based on susceptibility testing results. At 12 hours, spirochetes were no longer visible on the peripheral, and the patient became afebrile. At the time of 36 hours of admission, the patient complained of chest and low-back pain. A repeat troponin was 0.28 mug/L. She was started on metoprolol and transferred to the cardiovascular unit for observation. At the time of 48 hrs, a repeat troponin was 0.96 mug/L. During the next 12 hours of supportive treatment, the thrombocytopenia improved (112 x 109/L), and angina and febrile illness resolved. She was discharged with instructions to follow up with her primary care provider within 10 days. Fourteen days after onset of the illness, the patient's platelet count had normalized to 235 x 109/L. Serological testing for Borrelia sp. was performed on specimens collected on day 1 (acute) and on day 120 (convalescent). The acute specimen was negative whereas the convalescent specimen was positive for antibodies to B. hermsi.