Is anisakiasis common in Japan? What is the reason? (2/2)

 Recently NHK News on-line carries the following investigative report:

アニサキス症 日本で多い？その理由とは？ (2/2)

2022年12月5日 18時07分

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一方で、韓国でも生で魚介類を食べる習慣があるためアニサキス症が起きてはいるものの、日本海側でとれた魚介類であることが多いため、日本と比べて発生件数は少ないとしている。

ということは日本海側の魚は安心して食べられるということなのだろうか。

国立感染症研究所 杉山客員研究員

「実はそうでもありません。最近になって日本海側の魚からもS型が発見されるようになりました。海洋環境の変化で回遊する魚が変わったことが原因と考えられています。今後の海洋環境の変化によってはアニサキスの生息地域が変わってくる可能性はあると思います。といってもP型やシュードテラノバでもアニサキス食中毒にはなりますので、やはり注意が必要です」

アニサキスの寄生が少ない魚は？

では、アニサキスの寄生が少ない魚はいるのか、杉山客員研究員にきいたところ、内海にいる魚種はアニサキスの寄生が少ないと言われているということだった。

取材を進めると、実際にブランド魚の「関さば」にアニサキスの寄生率が少ないという研究が発表されていたことが分かった。

大分県沖の豊後水道で1本釣りされる「関さば」は、元々、地元の漁業関係者や料理人の間では、アニサキスの寄生が少ないと言われてきたという。

しかし、科学的なデータがないため、その実態は不明だった。

そこで立ち上がったのが、大分大学の小林隆志教授の研究チームだ。

2014年から2016年にかけて、地元の漁協などの協力を得て、「関さば」74匹、九州西部でとれたさば40匹、そして九州南部の40匹を解剖して寄生するアニサキスをすべて取り出し、それぞれの寄生率について調査をした。

その結果、

▼関さばのアニサキスの寄生率が6.8％だったのに対し、

▼九州西部は75％、

▼九州南部は38％だったというのだ。

大分大学 小林隆志教授

「今回の調査で、関さばのアニサキス寄生率が少ないことが実証されました。ただ、その理由はまだわかりません。ほかの海域の群れとほとんど交わらず、独立している群れのことを『系群』といいますが、関さばも『系群』を形成していると言われています。これは推測の域を出ていませんが、関さばは瀬戸内海を周遊してアニサキスの寄生が少ない独特の『系群』を作っているのではないかと言えます」

では、関さばは生で食べても安全ということなのか。

大分大学 小林隆志教授

「残念ながら『安全』とは言い切れません。実際に寄生率6.8％という低い数値ながらアニサキスは寄生しています。生で食べるときには通常通り注意が必要です」

また、大分県漁業協同組合佐賀関支店は、「もともと寄生率が少ないとはきいていましたが、全国的にアニサキス症が増加する中で、今回実証してもらったことでより安心を得られた」と話している。

生の魚に瞬間的に電気を流してアニサキスを殺虫する技術も開発されたが、本格的な導入はまだ先で、残念ながら生の魚を食べるときには注意しなければならないのが現状のようだ。

アニサキスは、健康診断の際などに無症状のまま胃に刺さっていることが偶然見つかることもある。

こうしたことからアニサキス症は、刺さったことの痛みだけで生ずるのではなく、アレルギー反応もあるのではないかと言われているが、その発症のメカニズムもまだ解明されていない。

アニサキスで苦しむ人が1人でも少なくなるよう、私は、引き続き取材を続けていきたい。

アニサキスに注意するために

魚に脂がのってよりおいしくなる時期だが、生で食べる際には、

▼購入前や調理前には必ずアニサキスがいないかを確認し、見つけたら必ず取り除くこと

▼新鮮な魚を購入し、釣った魚の内臓はすぐ取り除くことを忘れずに

▼塩やわさび、醤油や食酢をかけても通常の量では死なないので注意が必要

Translation

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On the other hand, even though anisakiasis also occurred in South Korea where there was a custom of eating raw seafood, the incidence of anisakiasis was lower than in Japan because most of the seafood was caught on the Sea of Japan coast.

Does that mean that fish from the Sea of Japan side could be safely eaten?

National Institute of Infectious Diseases Visiting Researcher Sugiyama

"Actually, that's not the case. Recently, S-types have also been found in fish on the Sea of Japan coast. It is believed that this is due to changes in migratory fish because of changes in the marine environment. I think that the habitat of Anisakis may change depending on changes in the marine environment. However, even P-type and Pseudoterranova can cause Anisakis food poisoning, so we still need to be careful.”

Which fish had less Anisakis parasite?

Then, when I asked visiting researcher Sugiyama, whether there were any fish had less Anisakis parasite, I was told that fish species in the inland sea were said to be with less Anisakis parasite.

As I proceeded with the interview, I learned that a study had been published showing that the rate of Anisakis parasitism was actually low in the brand name fish "Seki mackerel".

“Seki mackerel” which was caught by single line fishing in Bungo Channel off the coast of Oita Prefecture originally had been said among local fishermen and chefs that they were less parasitized by Anisakis.

However, due to lack of scientific data, the actual situation was not known.

That was why the research team led by Professor Takashi Kobayashi of Oita University was set up.

From 2014 to 2016, with the cooperation of local fishermen's cooperatives etc., 74 "Seki mackerel", 40 mackerel caught in western Kyushu, and 40 mackerel caught in southern Kyushu were dissected and all Anisakis parasites were taken out. Respectively their parasitic rate was investigated.

The results were,

▼While the overall Anisakis parasitic rate of in Seki mackerel was 6.8%,

▼ In Western Kyushu it was 75%,

▼ In Southern Kyushu it was 38%.

 Professor Takashi Kobayashi, Oita University

"This study demonstrates that the rate of Anisakis parasitism in the Seki mackerel is low, but we still don't know why. Schools that rarely intersect with other sea areas and are independent are called "system groups", but it is said that Seki mackerel also form "system groups". This is only speculation, but it can be said that Seki mackerel may have circumnavigated the Seto Inland Sea to create a unique 'system group' that has less Anisakis parasites."

So, is Seki mackerel safe to eat raw?

Professor Takashi Kobayashi, Oita University

"Unfortunately, it cannot be said that it is 'safe'. In fact, Anisakis is parasitic even though the parasitic rate is as low as 6.8%. As usual, caution is required when eating raw."

In addition, the Saganoseki branch of the Oita Prefectural Fisheries Cooperative was saying that, ``While had heard that the parasitic rate was originally low, yet anisakiasis is on the rise nationwide now, we have gained more peace of mind with this actual proof.”

While a technology had been developed to kill Anisakis instantaneously by passing electricity through raw fish, its full-scale introduction was still a long way off; it was unfortunately as it seemed that the current situation was that people had to be careful when eating raw fish.

Anisakis was sometimes found by chance to be stuck in the stomach without any symptoms, such as during a health checkup.

For these reasons, anisakiasis was thought to cause not only a pain by a sting, but also by an allergic reaction, but the mechanism of its onset had not yet been elucidated.

I would like to continue reporting so that the number of people suffering from Anisakis could decrease even by one.

To be beware of Anisakis

While it was the time to eat as the fish became more oily and tastier, yet when eating it raw,

▼ Before purchasing or cooking, be sure to check for Anisakis, and if you found it, be sure to remove it.

▼ To buy fresh fish; and didn't forget removing the internal organs immediately after you caught it.

▼Be aware that even if you put in salt, wasabi, soy sauce, or vinegar, with the normal amount the Anisakis would not die.

              So, one of the main reasons why Anisakis is so common in Japan is its food culture of eating raw fish, such as sashimi and sushi. There are several ways to avoid Anisakis: 1. Before purchasing or cooking, be sure to check for anisakis, and if you find it, be sure to remove it. 2. To buy fresh fish, and don't forget removing the internal organs immediately after you catch it. 3.Be aware that even if you put in salt, wasabi, soy sauce, or vinegar, the normal amount used will not be enough to kill Anisakis.