A 69-year-old, Japanese man underwent a scheduled screening colonoscopy, following a positive stool occult blood test. Colonoscopy revealed a mobile foreign object, which appeared whitish in white light (Fig. 1A). The object was showed extremely strong adherence to the mucosa of the ascending colon. The 20-mm long nematode was extracted using forceps (Fig. 1B) and identified as Anisakis spp. (Fig. 1C). Although the patient had consumed mackerel-sushi 3 days ago, there were no symptoms. Upper endoscopy screening performed on the same day did not show any anisakiasis-related changes or Anisakis itself.
Anisakis is globally prevalent and frequently infects consumers of raw or barely cooked fish. Although gastric anisakiasis is common in Japan, colonic anisakiasis is rarely reported. Furthermore, asymptomatic colonic anisakiasis is very rare. To our knowledge, there exist only 6 cases (including our case) in the English literature globally. Anisakis was found in the ascending colon in 3 cases and in the descending colon, sigmoid, and rectum in 1 case each. Three cases were caused by mackerel and one each by bonito, anchovy, and an unknown source. As no anthelmintic agents are available for this nematode, endoscopic removal of the Anisakis is required in acute cases.
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FundingThe authors have not received any grant for this research from any funding agency in the public, commercial, or not-for-profit sectors.
Conflict of interestsNone declared.
