Cannot be treated with dewormer... 'National Fish' mackerel found to contain whale roundworm causing food poisoning

Recently, in mackerel caught off the east coast, there have been whale roundworms that can cause food poisoning symptoms.

Japanese media reports have emerged indicating that large quantities are being discovered.

On the 21st, the Nihon Keizai Shimbun (Nikkei) reported that from 2019 to 2021, the mackerel fillet parts caught in the Pacific contained an average of 15.3 whale tapeworms per fish, which was higher than the 2.1 found in mackerel from the East Sea. However, recent tests on mackerel from the East Sea also detected large quantities of whale tapeworms, reducing the gap. In the two East Sea areas caught in 2022-2023, an average of 13.6 and 9.7 whale tapeworms per fish were detected.

The whale roundworm that parasitizes seawater fish includes types such as As, which easily moves from the internal organs to the flesh, and Ap, which is difficult to move within the fish's body. In the past, the whale roundworm found in mackerel caught in the East Sea contained little As, but recent investigations have confirmed that large amounts of As are now also detected in mackerel from the East Sea.

This roundworm is known to have whales as its final host and is called whale roundworm. It reaches whales ultimately through the food chain of fish and marine mammals. The eggs of the whale roundworm are widely dispersed in the sea through whale feces. The larvae grow in water and then migrate to crustaceans, various fish, and squid before reaching the whale, where they become adults and lay eggs. When the host is alive or in a fresh state, it is a nematode that lives inside the intestines. However, if the parasitic fish or marine mammals die, it has the characteristic of piercing through the intestines and moving into the muscles.

Consuming raw or undercooked fish such as sushi can cause symptoms similar to food poisoning. However, AP is known to have a lower risk of infection than AS when only the internal organs are removed.

Usually, when a fish infected with whale roundworm is eaten, symptoms such as abdominal pain, nausea, vomiting, and cold sweat occur 2 to 4 hours later. These symptoms are similar to gastritis and gastric ulcers. Whale roundworms tend to penetrate the stomach wall, causing symptoms like stabbing pain and vomiting when infected. They cannot be treated with common deworming medications, and surgical removal of the larvae is the only treatment.

Visiting researcher Hiroshi Sugiyama from the National Institute of Infectious Diseases in Japan stated, "The risk of food poisoning symptoms from consuming mackerel caught in the East Sea has become not significantly different from that in the Pacific Ocean," adding, "The cause is not clear, but it may be related to changes in seawater temperature or ocean currents."

To avoid infection with whale roundworms, cook the fish in boiling water at 70°C or higher for at least one minute. If you want to eat fresh sashimi, it is better to cut the sashimi into small pieces. During the cutting process, the thin and long whale roundworms are cut and killed.

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When eating mackerel, you must make sure to cook it thoroughly and properly.

You should be especially careful with the internal organs~