A 45-year-old man presents with nausea, photophobia, and a continuous generalized headache for one day; and a fever of 102.2˚F (39˚C) for two days. There is no history of weakness, vomiting, loss of consciousness, or seizures. He returned from Vietnam three days before the onset of symptoms; he spent two weeks there as a tourist. During that time he was bitten by insects on multiple occasions, and he ingested raw seafood and drank fresh water. His medical and surgical histories are unremarkable. He is not on any medications. There is no history of allergies. He drinks socially, does not smoke, and denies recreational drug use. He has had a single stable partner for the last 10 years. There is no history of blood transfusions. A full blood count, liver profile, renal profile, urinalysis, ECG, and chest x-ray are all unremarkable.