A 28-year-old male from rural Bihar presents with fever, chills, and sweating for 3 days. He reports a history of similar episodes occurring every 48 hours over the past 2 weeks. On examination, he is febrile (39.5°C) and has mild hepatosplenomegaly. A peripheral blood smear prepared during fever shows ring forms and Schüffner's stippling within RBCs. What is the most likely diagnosis?