A healthy 20-year-old Japanese man presented to the hospital with a ribbon-like object protruding from his anus (Figure 1A). He frequently enjoyed eating sushi, and he especially loved raw salmon. He had never traveled outside of Japan. He reported bowel irritation, mild diarrhea, and 3 kg of weight loss over the course of the previous 3 days. Blood test results were unremarkable, and there was no evidence of anemia. He had been diagnosed with Vibrio parahaemolyticus infection the previous year after consuming uncooked whitebait.
On examination, he had a yellow, flat, ribbon-like object entangled in toilet paper protruding from his anus. The ribbon-like object, which was segmented and had a spoon-shaped head, was identified as a tapeworm (Figure 1B and 1C). The diagnosis was consistent with the patient’s preference for raw salmon; however, the identification of eggs or proglottids in the stool was required for a definitive diagnosis.
The patient was treated with a single dose of praziquantel while hospitalized; however, no eggs or segments of the worm were identified in his feces. It was surmised that the entire body of the worm and all eggs had been evacuated before hospitalization. His bowel irritation and mild diarrhea resolved, and he has not reported any recurrence since the time of discharge.
Diphyllobothriasis is a zoonosis caused by a particular genus of fish tapeworm acquired from ingesting infected raw or undercooked fish, especially in Japan; salmon infected with Dibothriocephalus nihonkaiensis is often implicated.1 Such cuisine is now prevalent worldwide, and it is currently estimated that more than 20 million people are currently infected with this cestodosis, making it the most common zoonosis worldwide.2 A recent taxonomic and genetic survey subdivided some members of the genus Diphyllobothrium into the genera Dibothriocephalus, Adenocephalus, and others.3
Because tapeworm infection sometimes causes vitamin B12 deficiency, information about previous ingestion of fresh or undercooked fish should be sought for patients with megaloblastic anemia.3,4 However, the diagnosis should be confirmed by checking for ova or proglottids in the patient’s stool.2 Additionally, broad tapeworms are sometimes found during colonoscopy.5
Tapeworm eggs have an operculum at one end, and the genital pore and uterus are situated in the center of each proglottid.6 Although we did not confirm the presence of eggs, based on the food preference of the patient, we believe this tapeworm was of the genus Diphyllobothrium.
Because globalization has resulted in the consumption of sushi and other forms of raw fish worldwide, and because the prevalence of zoonoses has increased, any clinician may encounter parasitic diseases.
We thank Takashi Iwaki, DVM, PhD, of the Meguro Parasitological Museum for constructive advice regarding how to revise the manuscript.
Ikuno H, Akao S, Yamasaki H, 2018. Epidemiology of Diphyllobothrium nihonkaiense Diphyllobothriasis, Japan, 2001–2016. Emerg Infect Dis 24: 1428–1434.
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