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Background Japanese encephalitis is a potentially life-threatening complication of exposure to Japanese Encephalitis Virus (JEV), a flavivirus transmitted via Culex species mosquitos.Methods Retrospective case analysis of a patient diagnosed with ultimately fatal Acute Encephalitis Syndrome (AES) with discussion of clinical presentation and diagnostic challenges.Results A 70-year-old man became acutely unwell whilst caravaning near the New South Wales/Victorian border. The medical background was well-controlled hypertension, benign paroxysmal positional vertigo, and osteoporosis with recent vertebral compression fractures. He presented to a regional hospital with headache, reduced oral intake, fever and confusion. He deteriorated further and developed focal seizures affecting the face and upper limbs. He was intubated within 72 hours of initial presentation, commenced on anti-seizure medications and transferred to a centre nearer home. Initial CSF analysis demonstrated elevated protein (1.08g/L), normal glucose and high mononuclear cell count (104x10^6/L). MR head showed abnormal T2/FLAIR hyperintensity in the bilateral thalami. The clinical trajectory was one of persistent severe encephalopathy with diffuse cerebral dysfunction on electroencephalogram, ongoing fevers, and liver function test derangement. He tested negative on multiplex PCR testing for common CSF pathogens and CSF cryptococcal antigen was negative, however demonstrated immunoglobulin G seroconversion to JEV in serum. There was no significant neurological recovery, and palliative measures were instituted. The patient died 23 days after symptom onset.Conclusion This case discusses diagnostic approaches to JEV, imaging findings typical of acute Japanese encephalitis and reminds us of the changing epidemiology of certain infectious diseases in light of global climate change.