A 42-year-old woman from Virginia, USA, presents with a 5-day history of fever (39.2°C), severe frontal headache, and myalgia. On examination, she has a petechial rash that began on her wrists and ankles 2 days ago and has now spread to involve the trunk, including the palms and soles. She reports a tick bite on her leg 8 days ago while hiking. Platelet count is 95,000/μL (mild thrombocytopenia). What is the most likely diagnosis?