Japanese encephalitis (JE) is critical epidemic encephalitis caused by the JE virus (JEV) in Southeast Asia. The World Health Organization defined "acute encephalitis syndrome" (AES) as an acute onset of fever with a change of mental status and/or new-onset seizure, mainly for the surveillance of JE. The key clues for the diagnosis include the patient age group of unvaccinated era or waning vaccine-induced immunity and the history of possible mosquito bites in epidemic areas. We report a 47-year old man who is in an unvaccinated era with potential waning immunity. The patient presented with fever and altered mental status for 2 days. He was speechless and could not follow commands. The patient had gone camping in the countryside a week before the visit. At the emergency department, neck stiffness was noted. There was a leukocytosis with a left shift by blood cell count. The brain computed tomography was essentially normal. The cerebrospinal fluid (CSF) sample via lumbar puncture showed leukocytosis, a high protein level, and a low sugar level in comparison to serum tests. Further antibody test of CSF confirmed the diagnosis. Magnetic resonance imaging (MRI) of the brain revealed a high signal in the right thalamus and a mildly swollen left caudate nucleus 4 days after admission. He was extubated and finally discharged with partial dependency on activities of daily living. This case reminds us of the JE in AES. Emergency physicians should be aware of the suspicious case of unvaccinated age or waning immunity and possible mosquito bites in epidemic areas. The role of MRI on JE was also discussed in this article.
Keywords: Japanese encephalitis; acute encephalitis syndrome; meningitis.