Borrelia — Lyme, Relapsing Fever

A 28-year-old man from rural Rajasthan presents with recurrent episodes of high fever (39.5°C), headache, myalgia, and chills occurring at 5–7 day intervals over the past 3 weeks. Each febrile episode lasts 2–3 days, followed by an afebrile period of 4–5 days before fever recurs. He reports a tick bite 4 weeks ago. Blood smear during a febrile episode shows spirochetes. What is the causative organism and the mechanism of its antigenic variation?

A 32-year-old woman from Himachal Pradesh presents with a 3-week history of migratory joint pain, myalgia, and low-grade fever. She recalls a tick bite 2 months ago while hiking in a forested area, followed by a characteristic expanding erythematous rash at the bite site that faded over weeks. On examination, she has mild knee effusion bilaterally and normal neurological examination. Serology for Borrelia burgdorferi is positive by ELISA. What is the most appropriate next step in management?

Which vector is responsible for transmission of Borrelia burgdorferi in Lyme disease?