Tokyo Food Safety Information Center » Good things to know »Food parasites »Kudoa septempunctata - Myxosporidia

Kudoa septempunctata - Myxosporidia

In recent years, cases of food poisoning have occurred across the country where the cause was unclear. Symptoms included transient vomiting and diarrhea several hours after eating, ultimately resulting in victims experiencing minor illness. What many of these cases shared in common was that fresh fish, especially olive flounder sashimi, had been served. An investigation conducted by the Ministry of Health, Labour and Welfare revealed that Kudoa septempunctata, a parasite found in olive flounder, can cause symptoms such as diarrhea in humans.
Food poisoning from Kudoa septempunctata can be prevented by freezing or cooking olive flounder.
Conversely, while eating olive flounder raw is popular, freezing it reduces the quality of the meat and, as such, research is currently exploring means other than freezing for preventing Kudoa septempunctata food poisoning. Initiatives are also being implemented in areas where olive flounder is produced (aquaculture farms) such as monitoring tests prior to shipping and cleaning of breeding environments.

Kudoa septempunctata characteristics

Size Approximately 10 micrometers
Characteristics Spores: Parasitize olive flounder muscle tissue
The details of the Kudoa septempunctata life cycle are still unknown.
In other parasites in the Kudoa genus whose life cycles are understood, the organisms generally move back and forth between parasitizing annelids such as Hediste and fish and do not spread directly between fish. Accordingly, it is believed that Kudoa septempunctata does not transfer between fish in aquaculture farms and tanks.
ヒラメ筋肉中の偽シスト 偽シストの中には多数の胞子が入っている クドア・セプテンプンクタータの胞子
Pseudocyst in olive flounder muscle tissue   Kudoa septempunctata spores

Effects on people

When an olive flounder parasitized by a large number of Kudoa septempunctata (around 10 × 107 Kudoa septempunctata spores per gram of muscle tissue) is eaten by a human, the parasite causes symptoms such as transient diarrhea and vomiting several hours after eating. Such symptoms are slight in degree and recovery is rapid.
Cases of Kudoa septempunctata food poisoning tend to occur most often in summer (August to October) and only in small numbers from winter to spring (November to May).

Parasitized fish

Olive flounder

Prevention methods

Freeze olive flounder meat at -20° C for at least 4 hours or cook at 75° C for at least 5 minutes to prevent Kudoa septempunctata food poisoning.

Countermeasures taken at aquaculture farms

Existing investigations show that that the ocean regions in which Kudoa septempunctata parasitization has been confirmed in aquaculture farms are limited. They also indicate that there is a high possibility that cases of Kudoa septempunctata parasitization spreading in aquaculture farms were due to the movement of parasitized fry (juvenile fish).
Accordingly, in order to prevent food poisoning from olive flounder, a variety of countermeasures are being taken at aquaculture farms.
Main countermeasures taken at aquaculture farms

  • The introduction of fish not parasitized by Kudoa septempunctata.
  • Breeding management to prevent the mixing of olive flounder with differing breeding histories.
  • Securing breading environments where annelids such as Hediste do not live.
  • Properly managing breeding histories.
  • Conducting testing to confirm an absence of Kudoa septempunctata parasitization prior to shipping.

Currently, the life cycle of Kudoa septempunctata is not fully known. Accordingly, it difficult to establish specific methods for reliably preventing Kudoa septempunctata parasitization in olive flounder, and research is continuing to be conducted.


Life cycle
The cycle from parasite egg to larva to development into the adult form and the production of the next generation. When the life cycle of a parasite is understood, it is possible to prevent its parasitization by stopping any of its stages.

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