Colonic anisakiasis incidentally detected during colonoscopy

A previously healthy 48-year-old Japanese woman underwent a routine medical examination. Her vital signs were normal. During the physical examination, her abdomen was soft and non-tender. Incidentally, a colonoscopy showed a white worm penetrating the mucosa of her descending colon (Fig. 1a). Further questioning revealed that 2 days earlier, she had eaten yellowtail (Japanese amberjack) and flounder sashimi. Based on the above findings, a diagnosis of colonic anisakiasis was confirmed. Endoscopic removal of the worm was successful (Fig. 1b). The worm was dead, likely due to bowel preparation. In addition, a blood examination indicated no abnormalities, including eosinophilia.

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FIG 1.

(a) White worm penetrating the mucosa of the descending colon, (b) view following removal of the worm (arrowhead)

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Anisakiasis is a parasitic disease caused by anisakis nematodes. The disease is transmitted when infective larvae are ingested through the consumption of raw/undercooked fish or squid. In most cases, the disease primarily affects the stomach, and the incidence of colonic anisakiasis is only 0.25%.¹ The distance from the mouth is considered to influence this gastrointestinal localisation.²

Common symptoms of anisakiasis include abdominal pain, haematochezia, and nausea.³ In some patients, mass formation, including a submucosal tumour, causes bowel obstruction or intussusception.^4,5 However, 40% of patients have been reported to be asymptomatic,³ as was this patient. Chronic anisakiasis can result in the formation of an abscess and/or granuloma; therefore, complete removal of the larvae is strongly recommended even in asymptomatic patients.³ Although effective treatment of anisakiasis with albendazole has been reported, the evidence is limited. In Japan, there are no anthelmintics approved for use for anisakiasis. With the globalisation of food culture and the increased use of colonoscopy, the incidence of colonic anisakiasis is expected to rise.