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Intense stomach pain after eating fish – food poisoning from Anisakis

Due to the Japanese cultural practice of eating raw seafood such as sushi and sashimi, cases of digestive system illnesses are much more common than other countries, with 500 to 1,000 occurring each year.
In line with the development of extensive distribution systems for fresh and live seafood, a great variety of seafood species have come to be eaten raw habitually. And this list includes fish which are parasitized by an organism called Anisakis. Accordingly, there is a possibility that cases of food poisoning caused by Anisakis will increase going forward.

What is Anisakis-induced food poisoning?

Anisakis is a parasite which grows into its adult form inside marine mammals such as whales and dolphins; its larvae, meanwhile, parasitize fish such as mackerel and Todarodes. When seafood which carries Anisakis is eaten raw or in a near raw sate, Anisakis enters the stomach and intestinal wall of human beings, causing gastroenteritis, also called “Anisakis disease.”
Anisakis disease frequently occurs within eight hours after eating parasitized seafood and mainly causes intense stomach pain. This may also be accompanied by nausea and vomiting.

Click here to learn more about Anisakis

図 腹痛の男性

 

Which species of fish does Anisakis parasitize?

Mackerel, salmon, Pacific herring, Todarodes, sardine, and Pacific saury are known to be carriers. In addition, according to a study on the state of parasites conducted by the Tokyo Metropolitan Institute of Public Health up to 2009, it was found that Okhotsk atka mackerel, Japanese Spanish mackerel, splendid alfonsino, young tuna, and fat greenling are also parasitized by Anisakis. Conversely, unless given live bait already parasitized by Anisakis, the parasitization of farmed fish by Anisakis is virtually unknown.
The eggs of Anisakis are excreted together with the feces of its final host – marine mammals such as whales. After hatching from these eggs, Anisakis is eventually eaten by a type of plankton called krill, inside of which it grows into L3 larva. As Anisakis can spread not only from krill to the fish which prey on krill but also fish which prey on fish infected with Anisakis, a great variety of fish are parasitized by this organism.

Will using vinegar kill Anisakis?

Anisakis cannot be killed by the amounts of vinegar used in normal cooking. In fact, cases of Anisakis disease have occurred which are believed to have been caused by vinegared mackerel.
Similarly, Anisakis also cannot be killed by the amounts of wasabi, soy sauce, and other condiments normally used for cooking.

Are there any precautions which should be taken when storing seafood?

In general, Anisakis more frequently parasitizes the organs of fish over their muscle tissue.
Experiments conducted by the Tokyo Metropolitan Institute of Public Health have found that leaving seafood to sit at room temperature makes it easy for Anisakis to move into muscle tissue. Accordingly, when planning on eating raw fish, it is important to choose fresh products, remove internal organs as quickly as possible, and store seafood at low temperatures (4° C or less).
Fig: Fish

Key points for preventing Anisakis-induced food poisoning

  • Anisakis can be killed through cooking or freezing. As such, heat seafood sufficiently to ensure the penetration of heat to the center or freeze until seafood is completely frozen to the center (at -20° C for at least 24 hours).
  • When planning on eating raw fish, choose fresh products, remove internal organs as quickly as possible, and store seafood at low temperatures (4° C or less).
  • When preparing fish for eating raw, be aware of Anisakis and check carefully for its presence. Take particular care when preparing meat close to organs (such as the stomach).
  • Anisakis’ ability to penetrate into the stomach and intestinal wall declines considerably when it is damaged; accordingly, when preparing dishes such as namero (chopped seasoned fish), chop the meat finely.

Message for businesses

When handling seafood with a high possibility of Anisakis infection at restaurants and stores, cooking or freezing the fish completely to its center (-20° C for at least 24 hours) are effective means of preventing food poisoning. When cooking or freezing are difficult, remove internal organs as quickly as possible and store at low temperature (4° C or lower). In addition, take measures such as warning customers and conducting a visual check of fish, sashimi, and sushi when preparing or serving the same.

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