Parasite - Incidence of Anisakis in Japan

 An interesting report in this month's Emerging Infectous Disease involves Anisakis, a parasite commonly linked with raw or undercooked seafood, and its incidence in Japan, a country that consumes a large amount of raw seafood in the form of sushi and sashimi.  Researchers estimated that the annual incidence is close to 20,000 cases per year.  I think that many people assume that sushi and sushimi represents zero risk, especially when we think of Japan.  This is not the case.

"In Japan, A. simplex s.s. nematodes are responsible for the highest incidence of anisakiasis, whereas the species A. pegreffii is the leading cause of anisakiasis in Europe and South Korea (2). A. simplex s.s. nematodes penetrate the muscles of various fish species at a higher rate than A. pegreffii (11), which could partly explain the smaller proportion of A. pegreffii anisakiasis cases in Japan because A. pegreffii nematodes are often removed with fish viscera during the preparation of sushi and sashimi. Furthermore, fish habitat can corroborate the difference in predominant anisakid nematode species between South Korea and Japan; A. simplex s.s.–carrying fish are predominant in the Pacific side of Japan, whereas A. pegreffii–carrying fish are more common in the Sea of Japan and the East China Sea, located between South Korea and Japan (11)"

"As preventive measures, the government of Japan has repeatedly instructed local establishments (e.g., restaurants, fish mongers, and grocery stores) and consumers to freeze seafood at −20°C for at least 24 hours before consuming it raw or to remove anisakid nematodes during cooking."   In the US, there is no regulated standard for 'sushi grade seafood' but this term generally means that that the seller has determined that the fish is acceptable for eating raw based on several factors, including if that the fish has been frozen according to a validated freezing schedule for parasite reduction.

Anisakiasis, the disease caused by infection of this worm.  According to the CDC, "when certain infected marine mammals (such as whales or sea lions) defecate into the sea, eggs are released and become infective larvae while in the water. These larvae are ingested by crustaceans, which are then eaten by fish or squid. When humans eat raw or undercooked infected fish or squid, they ingest nematode larvae. Once inside the human body, the larvae can invade the gastrointestinal tract. Eventually, the parasite dies and produces an inflamed mass in the esophagus, stomach, or intestine."

"Some people experience a tingling sensation after or while eating raw or undercooked fish or squid. This is actually the worm moving in the mouth or throat. These people can often extract the worm manually from their mouth or cough up the worm and prevent infection. Also, some people experience vomiting as a symptom and this can often expel the worm from the body."

Anisakiasis Annual Incidence and Causative Species, Japan, 2018–2019 - Volume 28, Number 10—October 2022 - Emerging Infectious Diseases journal - CDC
ISSN: 1080-6059
Emerging and Infectious Disease Journal
Volume 28
Number 10—October 2022
Anisakiasis Annual Incidence and Causative Species, Japan, 2018–2019
Hiromu SugiyamaComments to Author , Mitsuko Shiroyama, Ikuyo Yamamoto, Takashi Ishikawa, and Yasuyuki Morishima

Author affiliations: National Institute of Infectious Diseases, Tokyo, Japan (H. Sugiyama, I. Yamamoto, Y. Morishima); Azabu University, Kanagawa, Japan (M. Shiroyama); BML, Inc., Saitama, Japan (T. Ishikawa)

Abstract

Using data from 2018–2019 health insurance claims, we estimated the average annual incidence of anisakiasis in Japan to be 19,737 cases. Molecular identification of larvae revealed that most (88.4%) patients were infected with the species Anisakis simplex sensu stricto. Further insights into the pathogenesis of various anisakiasis forms are needed.