Scientists find big discrepancy in anisaki estimates and official statistics

Researchers have estimated that Japan had around 20,000 cases of anisakiasis each year in 2018 and 2019. These numbers are much higher than official figures.

Anisakiasis is a parasitic disease caused by anisakid worms. Transmission occurs when infective larvae are ingested from fish or squid eaten raw or undercooked. The Japanese consume large amounts of seafood and it is common to have raw seafood, such as sushi and sashimi.

For anisakiasis, there is a big difference between food poisoning statistics from the Ministry of Health, Labor and Welfare and the actual incidence, the researchers said.

Using a database of health insurance claims from 2018 to 2019, scientists estimated the average annual incidence of anisakiasis in Japan at 19,737 cases. The database covers more than 8.4 million people per year, or about 6% of Japan’s total population.

The number of patients registered in the database was 991 in 2018 and 766 in 2019, found the study published in Emerging infectious diseases.

Researchers estimated that the number of people with anisakiasis in Japan was 21,511 in 2018 and 17,962 in 2019. The number of patients recorded in food poisoning statistics during the same period was considerably lower than 478 in 2018 and 336 in 2019.

More attention on Anisakis infection
The government of Japan has asked local establishments such as restaurants and fishmongers as well as consumers to freeze seafood at -20 degrees C (-4 degrees F) for at least 24 hours before consuming it raw or remove the anisakid worms during cooking.

The Ministry of Health, Labor and Welfare of Japan provides food poisoning statistics with information on fish species reported by patients and preparation procedures associated with infections to help consumers and fishmongers avoid anisakiasis.

Scientists also obtained 189 anisakid worm larvae isolated from 181 patients with anisakiasis in 30 of Japan’s 47 prefectures in 2018 and 2019. They identified 168 larvae of Anisakis simplex sensu stricto, 10 larvae of Anisakis pegreffii and 11 larvae of Pseudoterranova azarasi.

In Japan, Anisakis simplex parasites are responsible for the highest incidence, while Anisakis pegreffii parasites are the main cause in Europe and South Korea.

Symptoms of anisakiasis are abdominal pain, nausea, vomiting, abdominal distention, diarrhea, blood and mucus in the stools, and mild fever. Allergic reactions with skin rashes and itching, as well as anaphylaxis, may also occur. Treatment may require surgical removal of the worm.

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