Imported cystic echinococcosis caused by Echinococcus granulosus sensu stricto genotype G3 in Japan

A Japanese man in his 50s who had lived in high-altitude rural areas, including the Tibet Autonomous Region, Qinghai Province and western Sichuan Province in China, Mongolia, and northern India, for more than 25 years presented with abdominal distension. Imaging studies revealed a cystic lesion in the left hepatic lobe with a 15-cm diameter and water lily sign consistent with cystic echinococcosis (CE) stage CE3a according to the World Health Organization Informal Working Group on Echinococcosis classification. Serum Western blotting detected antigen bands (7 kDa and 17 kDa), thus supporting the diagnosis of CE. Laparoscopic left hepatectomy was performed after initiation of albendazole therapy. Histopathological findings were compatible with a hydatid cyst. An analysis of mitochondrial genes extracted from cyst wall tissue identified Echinococcus granulosus sensu stricto genotype G3, thus confirming the diagnosis of CE. This case highlights the importance of integrating a detailed travel history, imaging studies, serological testing, and molecular analysis when diagnosing imported CE in nonendemic countries such as Japan.