フラビウイルス感染症（日本脳炎）

Flavivirus Infection (Japanese Encephalitis)

日本脳炎は過去の感染症ではなく，本邦で今も発生する重要な神経感染症である。特に中年以上では中和抗体保有率が低く，夏〜秋季の急性脳炎では必ず鑑別に挙げるべきである。視床や黒質の病変に対応した高熱，意識障害，錐体外路徴候が特徴で，急性期と回復期の適切な検体採取と血清学的検査により確定診断に至る。本論では他のフラビウイルス脳炎の診断にも資する臨床的要点を整理する。

Abstract

Japanese encephalitis remains a clinically relevant neuroinfectious disease in Japan. Adults in middle- to older- age groups are at higher risk due to the low prevalence of neutralizing antibodies. Clinicians should consider this disease when encountering acute encephalitis during the summer-to-autumn season. High fever, impaired consciousness, and extrapyramidal signs are characteristic clinical features and correspond to frequent involvement of the thalamus and substantia nigra. A definitive diagnosis is achieved through appropriate sampling of acute- and convalescent-phase specimens together with specific serologic testing. This article summarizes key clinical points of Japanese encephalitis that also inform the diagnostic approach to other flavivirus encephalitides.