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Parasites in raw and undercooked fish can be cause of abdominal pain, doctors warn

BMJ 2017; 357 doi: (Published 15 May 2017) Cite this as: BMJ 2017;357:j2335
  1. Zosia Kmietowicz
  1. The BMJ

Asking patients with idiopathic abdominal pain whether they have recently eaten sushi may help establish a diagnosis, doctors have advised, after finding that such a patient had been infected with a parasite found in raw and undercooked fish.

Eating raw or undercooked fish or seafood is increasingly popular in Western countries, said doctors from Portugal in BMJ Case Reports.1

They recounted the case of a 32 year old, previously well man who had had severe epigastric pain, vomiting, and fever for a week. A blood test indicated mild inflammation and abdominal tenderness. But it was only when the man revealed that he had recently eaten sushi that the doctors suspected that he might have anisakiasis.

Anisakiasis is caused by eating raw or undercooked fish or seafood infected with nematode parasites of the species Anisakis. Symptoms can mimic an acute surgical abdomen.

Endoscopy showed that the larva of a worm-like parasite was firmly attached to an area of the man’s gut mucosa that was swollen and inflamed. After the larva was removed with a Roth Net, the man’s symptoms resolved immediately. Laboratory analysis showed that the larva belonged to the species Anisakis.

Most of the reported cases to date have been in Japan, where a raw fish diet is very common, said the authors. “However, it has been increasingly recognised in Western countries,” they added, and they advised clinicians to consider the condition in patients with pain, nausea, vomiting, and other complications such as bowel obstruction and bleeding, who have recently eaten raw or undercooked fish.


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