Colonoscopy-Based Diagnosis of Dibothriocephalus nihonkaiensis Infection Protruding into the Ascending Colon

We report two recent cases of diphyllobothriid cestode infection identified during colonoscopy in asymptomatic individuals in Tokyo, Japan. Both patients lacked distinctive dietary habits, consuming only commonly available raw fish. In one case, the tapeworm was found in the terminal ileum; in the other case, the parasite extended into the ascending colon, which is a rare site of detection during colonoscopy. Morphological features were consistent with Dibothriocephalus nihonkaiensis. Blood tests revealed no notable abnormalities. These cases underscore that such infections may occur even in individuals without high-risk dietary behaviors. With increased use of colonoscopy and the global consumption of raw fish, similar detections may become more common, emphasizing the need for clinical awareness, even in patients without recognized dietary risk factors.