Beware of parasites in raw/undercooked fish, warn doctors

An unseen hazard with eating raw or undercooked fish/seafood is on the rise in Western countries, where dishes, such as sushi, are becoming increasingly popular, warn doctors today in BMJ Case Reports.


The warning comes after they treated a 32 year old previously well man who had had severe upper gut (epigastric) pain, vomiting, and fever for a week.


A blood test indicated mild inflammation, and the area below his ribs was tender. 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/seafood infected with nematode parasites of the species Anisakis.


Endoscopy—the insertion of a long tube with a camera on the end down the gullet and into the stomach—revealed the larva of a worm-like parasite firmly attached to an area of swollen and inflamed gut lining.


After the larva was removed with a special kind of net, the man’s symptoms cleared up straight away. Laboratory analysis showed that the larva belonged to the species of Anisakis.


Most of the reported cases to date have been in Japan, where a raw fish diet is very common say the authors.


“However, it has been increasingly recognised in Western countries,” they add, and advise 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.


BMJ Case Reports: Aniskiasis: a growing cause of abdominal pain! Doi 10.1136/bcr-2016-218857.


12 May 2017.