A Case of Immature Diphyllobothrium Balaenopterae Infection in the Coastal Area of the Tohoku Region, Japan.

Abstract

Diphyllobothrium balaenopterae infection is a zoonosis mainly reported in Japan and it is associated with raw fish consumption. The reported cases in Japan show geographical clustering, mainly in the Pacific coastal areas and in western Japan. Reports from the Tohoku region are scarce, resulting in limited clinical awareness of this disease among local practitioners in Japan. A man in his 20s, residing in the Pacific coastal area of the Tohoku region, presented with diarrhea and the anal expulsion of string-like material. He had no notable past medical history but reported frequent consumption of raw juvenile Japanese anchovy 2-3 months prior to onset. Although taeniasis was clinically suspected, a fecal examination for ova was negative, thus complicating the diagnosis. GastrografinⓇ (amidotrizoate meglumine and sodium solution) spraying into the duodenum via endoscopy enabled the recovery of a 2.0-m immature tapeworm. A molecular biological analysis targeting the mitochondrial cox1 gene of the worm confirmed the diagnosis of a Diphyllobothrium balaenopterae infection. No further proglottid discharge or gastrointestinal symptoms occurred during the six-month clinical follow-up. This case highlights the clinical significance of considering D. balaenopterae, even in non-endemic areas, recognizing the limitations of stool ova testing in immature infections, and preserving the worm for molecular identification.