Acute Careniche
A 58-year-old man who works at a piggery near Griffith, New South Wales, is brought in one February with four days of fever and headache and one day of confusion. His wife says he has become slow to move and that his hands shake when he reaches for a cup. Temperature 38.9 degrees Celsius, mild neck stiffness, no rash. He has never left Australia. There have been clouds of mosquitoes around the irrigation channels all summer. Cerebrospinal fluid contains 90 x 10^6/L white cells (85% lymphocytes), protein 0.9 g/L and a normal glucose. Which one of the following is the most likely cause of his encephalitis?