A 64-year-old man with a travel history to Southern Minnesota is brought to the hospital's emergency room on July 15 by his brother. The brother said that the man had a 2-day history of fever, headache, and 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:

The symptoms are the most consistent with West Nile neurological disease, a rare complication of West Nile virus infections. West Nile virus: West Nile virus is the leading cause of arboviral encephalitis. Birds, paicularly crows are natural hosts. The virus is normally transmitted by mosquito bite, but can be transferred by blood transfusions, breastfeeding, and through the placenta. It causes asymptomatic disease in 80% of those infected, but 20% develop West Nile fever, and less than 1% develop West Nile neurological disease (WNND), which is more likely to occur in individuals older than 60 years of age.