A 64-year-old man living on a farm in southern Minnesota is brought on July 15 to the emergency room by his brother. The brother said the man had a 2-day history of fever, headache, and some vomiting, but today he appeared confused. He is confused by some of the simple questions you ask him. His spinal tap is clear with 75% PMNs and a head CT is normal. The most likely cause of his symptoms is