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May 12, 2017 — With the rise in popularity of sushi, doctors are warning of the dangers caused by parasites in raw or undercooked fish and seafood.Infections from anisakidosis, a parasite found in sushi, are on the rise, says a new study in the journal BMJ Case Reports. It highlighted the story of a 32-year-old man from Portugal who had severe stomach pain, vomiting, and a weeklong fever. It was traced to a parasite known as anisakis, which he’d picked up from eating sushi.

Anisakidosis — formerly known as anisakiasis or anisakiosis, and also called herring worm disease — is a parasitic infection. It is caused by eating raw or undercooked fish or seafood infected with small anisakis worms.

Symptoms include:

  • Severe abdominal pain
  • Nausea and vomiting
  • Diarrhea

In rare cases, it can be fatal. Most reported cases have been in Japan, where eating raw fish is common, but it is increasingly being seen in Western countries, the study says.

Case Study

After saying he had recently eaten sushi, doctors in Portugal suspected the 32-year-old man may have anisakidosis.

They inserted an endoscope — a long tube with a camera on the end — through his mouth into his stomach. Pictures revealed the larva of a worm-like parasite firmly attached to an area of his stomach, which was swollen and inflamed.

After doctors removed the larva with a special kind of net, the man’s symptoms cleared up quickly. Laboratory analysis showed that the larva belonged to the anisakis species.

Anisakis larvae range in length from 5 to 20 millimeters (about a fifth of an inch to about an eighth of an inch).

Study author Joana Carmo, MD, says the disease is fairly rare in Europe. Ninety percent of the cases are in Japan, and the disease is also frequent in Scandinavian countries due to cod liver consumption.

“However, in other European countries, fish infestation is probably more frequent than we thought,” Carmo says. She says one study showed that anisakis was found in 39.4% of the fresh mackerel examined from different fish markets in Granada, Spain.