A 25-year old farmer presented with history of high grade fever for 7 days and altered sensorium for 2 days. On examination, he was comatosed and had conjunctival hemorrhage. Urgent investigations showed a hemoglobin of 11 gm/dl, serum bilirubin 8 mg/dl and urea 78 mg/d1. Peripheral blood smear was negative for malarial parasite. What is the most likely diagnosis -