A 52-year-old man from Virginia, USA, presents with a 4-day history of high fever (39.8°C), severe headache, myalgia, and malaise. On examination, a petechial rash is noted on the wrists and ankles, which has spread centripetally to involve the trunk and extremities. Blood pressure is 110/70 mmHg. Laboratory findings show thrombocytopenia (platelets 78,000/μL), elevated creatinine (1.8 mg/dL), and hyponatremia (Na⁺ 128 mEq/L). A Weil-Felix test is positive. What is the most likely diagnosis?