Powassan Virus-Related Encephalitis in the Off-Season: A Case Report.

Arboviral infections, increasingly identified due to the effects of climate change, pose significant health risks. We present a case of meningoencephalitis due to Powassan (tick-borne Flavivirus) virus in a middle-aged man from Rhode Island, unexpectedly diagnosed in the winter season. Confirmatory plaque reduction neutralization testing (Centers for Disease Control) revealed elevated titers for Powassan virus >1:20,480. The cerebrospinal fluid analysis demonstrated lymphocytic pleocytosis. The case highlights the expanding seasonal and geographic range of arboviruses, necessitating year-round vigilance. No targeted therapies exist; management remains supportive as 40-60% of patients develop chronic sequelae, including persistent confusion, fatigue, and headache. Arboviral etiologies in patients with altered mentation must be prioritized on the differential, even outside of peak transmission seasons.