other monsters for survival. Having no particular  interest in us, most of them are relatively  

武装した怪物が生まれては 生存をかけて戦っている

harmless, as our immune systems deal with  their weapons easily. But there are exceptions.

人類に特段の関心はなく ほとんどは比較的無害だ

Naegleria fowleri is an amoeba  that has not only developed a  

免疫系が彼らの武器を 簡単に処理できる

deadly taste for human brains but is also a  match for our defences and stars in dramatic  

だが、例外もある

headlines. What happens when  this monster enters your body?

Naegleria fowleri というアメーバは 人間の脳を食べて死に至らせ、免疫系にも対応する

Naegleria fowleri is an amoeba, a microbe with a  nucleus, one of the smallest lifeforms on earth.  

劇的な見出しを飾るスターだ

It is a voracious hunter of bacteria and other  critters that it devours whole and rips into  

この怪物が体内に侵入したら 何がおきるのか？

pieces. Like many amoebea it is able to transform  into different stages that help it survive,  

Naegleria fowleri はアメーバだ

but most of the time Naegleria  fowleri is in its trophozoite stage,  

核を持つ微生物であり 地球上で最小の生物の一つだ

during which it looks like a squishy blob  with tiny arms and hunts, divides and thrives.

アメーバは、細菌や他の生物を丸のみして細断する 獰猛なハンターだ

Its natural home is in fresh water: ponds,  rivers, lakes and hot springs. But unfortunately  

他のアメーバと同様、Naegleria fowleri は 生存のために変形できる

it also feels happy in pipes, swimming pools,  fountains or spas when they are not properly  

ほとんどの場合、Naegleria fowleri は栄養体で

treated. The warmer the water, the more it thrives  and multiplies. So in the summer, when humans seek  

小さな腕を持つグニャグニャの塊で

to cool off and enjoy themselves, the chances  are highest that both species will interact.

それが狩り、分裂し、繁栄している

Because this makes it hard to avoid, millions of  people regularly have contact with the amoeba,  

本来の生息場所は淡水で 池、川、湖、温水などだが

especially in warmer climates, and many people  even seem to have antibodies against it.  

残念ながら、居心地のいい場所には パイプ、プール、噴水、温泉などもある

And this is mostly ok, you can even  swallow it without consequences.

適切な処置が無い場合だ

Things turn bad when people dive or swim in water  contaminated with the amoeba and water splashes  

水温が高いほど 盛んに繁殖していく

high up into their noses. In a single drop  of lake water there are millions of viruses,  

だから、人間が涼しさと楽しさを求める夏は

bacteria and amoebea and that isn't really a big  deal. But Naegleria fowleri is different. Let  

アメーバと遭遇する可能性が 最大になるのだ

us zoom into the nose of an unsuspecting victim  enjoying a great summer day and see what happens.

だから回避は難しく

First of all, the amoeba doesn't  really want to be inside your nose  

特に温暖な地域では数百万人が 定期的に接触しており

as it is not really looking for trouble,  it just wants to eat a few bacteria.  

抗体を持つ人が多数ですらあるようだ

Instead it is greeted by your natural defenses.  Unfortunately for humans, Naegleria fowleri  

まあ概ね問題はなく 感染せずに飲み込むことすら可能だ

happens to be exceptionally good at generally  flying under the radar of your immune system.  

アメーバに汚染された水を泳いだり潜ったりして 水が鼻の高さまでくると、事態は悪化する

For example, the inside of your nose is covered  by mucosa, a slime filled with chemicals that  

湖の水一滴には何百万という ウイルス、細菌、アメーバがいるが

kill or stun possible invaders or alert immune  cells. But Naegleria fowleri is not particularly  

大した問題ではない

bothered by them and instead calmly checks out the  scenery, mildly annoyed about the whole ordeal.

だが Naegleria fowleri は違う

Now, if you are unlucky, the tiny  critter stumbles over something  

夏の一日を楽しむ無防備な犠牲者の鼻を拡大し 何が起きるか見てみよう

that actually sparks its interest: Nerve cells.

第一に、アメーバは望んで あなたの鼻に入ったのではない

Your nose is filled with a large  network of olfactory nerve cells  

細菌を少し食べたいだけで トラブルは求めていないのに

that pick up molecules from the outside and  transmit their information to your olfactory bulb,  

あなたの免疫系に出迎えられる

the center of smell in your brain. To do  their job these cells talk to each other by  

困ったことに、Naegleria fowleri はなぜか 免疫系のレーダーを潜り抜けるのが非常にうまい

releasing various messenger chemicals and  recognizing them via specific receptors.  

例えば鼻の内側は 粘膜に覆われ

One of the most important of  these chemicals is acetylcholine.

含まれる化学物質は侵入者を殺すか気絶させ 免疫細胞へ警告する

Through sheer evolutionary bad  luck, Naegleria fowleri happens to  

だが Naegleria fowleri は特に困らない

have receptors that recognize acetylcholine.  

落ち着いて景色を眺めつつ この試練に少しイラつく程度だ

And it seems to attract them irresistibly, a  little like moths that are attracted by light.

もしあなたが不運なら

So as your olfactory nerve cells do their job,  using plenty of acetylcholine to talk to the  

この微生物は 興味をかきたてるものに出会う

brain, Naegleria fowleri enters your tissue. It  seems to follow the chemical signals upstream.  

神経細胞だ

Neutrophils, crazy suicide warriors begin to  attack the amoebae. Individually they have no  

鼻は嗅覚神経細胞の 巨大ネットワークで満ち

chance against them as the invaders are large and  pretty buff fighters, used to dealing with tough  

外界の分子を拾い、その情報を 脳内の嗅覚中枢である嗅球に伝える

enemies. So the defenders swarm the intruders  and kill them either by vomiting chemicals  

神経細胞は任務遂行のために 様々な伝達物質を出し

that punch holes into them or by literally  ripping parts of them off and devouring them.  

特定の受容体で認識して交流する

But the Naegleria fowleri train is still on track  and while the Neutrophil attacks slow them down,  

特に重要な伝達物質が アセチルコリンだ

they continue to follow the olfactory  nerves to their final destination:

進化上の不運により

Your brain.

Naegleria fowleri は偶然にも アセチルコリン受容体を持っており

This process can take between one and nine days  

その伝達物質に強く惹きつけられる 光に蛾が集まるように

and you'll probably not notice  anything during that time.  

嗅覚神経細胞が働くとき 脳への伝達に多量のアセチルコリンが使われ

Until the amoebae reach the olfactory bulb, the  center of smell and entrance to your brain. Your  

Naegleria fowleri が 組織に侵入するのだ

brain cells are nothing more than helpless victims  and they all release that wonderful acetylcholine.

伝達物質の上昇流を追うように

Naegleria fowleri initiates a massacre and  releases an onslaught of various attack molecules.  

狂気の特攻隊員である好中球が 攻撃を始める

Some of them are basically little bombs  that rip holes into your cells on contact  

一対一では勝ち目はない

so their pieces can be eagerly  consumed. But Naegleria fowleri  

アメーバは大型の戦士で 強敵との戦いに馴れているので

is now multiplying - and it's also becoming  really creepy. In a feeding frenzy it can  

好中球はアメーバに群がり 身体に穴をあける化学物質を吐いたり

develop up to a dozen suckers called food cups,  that look like giant eerie mouths. The amoebae  

身体の一部を切り取って 食い荒らしたりして殺す

engage your brain cells, suck them in and  rip large “bites” out of them while they  

だがアメーバの進路に変更はなく 好中球の攻撃でもたついても

are still alive. Now things escalate quickly  and the disease that will kill you sets in.

嗅覚神経に沿って 目的地に向かい続ける

Alerted by the massacre, millions  of immune cells, Neutrophils,  

あなたの脳だ

Eosinophils and microglias invade the  infected tissue. Which is a problem:  

このプロセスには1～9日かかり その間はたぶん、何も気づかない

your immune system is dangerous and not  exactly a careful fighter. It's like  

しかしそれも嗅覚の中枢であり 脳の入り口である嗅球にたどり着くまでの話だ

burning down a forest to kill the wolves  inside it. A really bad idea in the brain.

あなたの脳は無力な犠牲者であり

They waste no time and attack the amoeba,  using all the weapons available to them,  

魅力的なアセチルコリンを わざわざ放出している

from chemicals to trying to eat them  alive. Neutrophils explode themselves  

Naegleria fowleri は大虐殺を始め 様々な攻撃分子を猛烈に放出する

to erect barriers spiked with deadly  chemicals. A fierce battle ensues.  

分子の一部は、接触した細胞に穴を空ける小型爆弾で 破片にむしゃぶりつける

Naegleria fowleri can actually fight back,  itself attacking and killing many immune cells.

ここで、このアメーバは増殖を始め いよいよバケモノじみていく

The immune system now throws everything it has at  the invader but in vain. The complement system,  

食欲が暴走し、巨大で不気味な 口のような吸盤が1ダースほど作られる

tiny protein bombs that can kill intruders on  their own, are easily disabled. Antibodies,  

アメーバはあなたの生きた脳にとりつき 吸い込み、嚙みちぎっていく

usually one of your superweapons, are just  destroyed or swallowed. A high fever that  

事態は急速にエスカレートし 死に至る病が発症する

usually slows enemies down does nothing,  as the amoeba actually thrives in the heat.  

大虐殺を受け、好中球、好酸球、ミクログリアが 何百万と感染組織に侵入する

All the while the amoebae continue to  multiply, fight and devour your brain cells.

問題は、免疫系は本来危険なもので 慎重には戦わないことだ

A disastrous chain reaction is taking place.  

森の中の狼を殺すのに 森を焼き払うようなもので

One major thing your immune cells do when  they fight is to cause inflammation. Which  

脳においては最悪の発想だ

directs large amounts of fluid from your  bloodstream into the site of an infection.  

ただちに免疫系は攻撃を始める 化学兵器から直接の捕食まで、あらゆる手段でだ

So as the battle rages on without a clear  winner, more and more fluid enters the brain.

好中球は自爆し 致死的な化学兵器を含むバリアを張る

At this point the human will feel  symptoms that quickly escalate.  

壮絶な戦闘だ

It all begins pretty vaguely, a headache, fever,  

Naegleria fowleri も反撃でき 多くの免疫細胞を攻撃し死滅させる

nausea and vomiting. As the battle spreads  rapidly through the brain serious symptoms appear,  

免疫系は全てを侵略者にぶつけるが 無駄に終わる

from confusion, inability to concentrate  to fatigue, seizures and hallucinations.  

侵入者を殺せる小さなタンパク爆弾 「補体系」も容易に無効化される

The brain swells up massively but can't expand due  to the bones surrounding it. So it compresses and  

超兵器のはずの抗体も ただ壊されるか飲み込まれる

disables the brainstem that controls things like  breathing. Usually within a week the patient dies.

侵入者を鈍らせる高熱も無意味だ

Up to 97% of patients infected by the  amoeba share this fate. In almost all cases,  

高温で繁栄しているのだから

by the time an infection by Naegleria fowleri is  recognized the disastrous battle for the brain  

その間もアメーバは増殖し、戦い続け あなたの脳を食い荒らしていく

is already so far along that there is almost  nothing to be done. Not only do we currently  

悲惨な連鎖反応が生じる

not have effective treatments, there are also an  abundance of open questions about how an amoeba  

戦闘モードの免疫細胞は 炎症を生じさせる

that usually enjoys its life in open water, is  able to overcome our immune system so effectively.

その結果、血管から大量の体液が 感染部位に流れ込む

So how worried do you need to be about this  horrifying killer amoeba? Well, not very. While  

決着が遅れるほど さらに体液が脳に流れ込んでいくのだ

the Naegleria fowleri is clearly extremely deadly  and the infection truly horrible, there have only  

ここで人間は 症状の急激な悪化を感じる

been a few hundred cases in the last few decades.  You are way more likely to drown in a pool than  

まずは漠然とした症状の 頭痛、発熱、吐き気、嘔吐から始まり

to get infected. Not only does the amoeba need  to be flushed high up your nose, it also needs  

脳内の戦闘が激化すると 症状も深刻化する

to get a good grip and it also has to make its  way through the first lines of your defences.

混乱、集中力の欠如、疲労、発作、幻覚などだ

Ultimately Naegleria fowleri is neither evil  nor a huge public health risk. But every year  

脳は強く膨張するが 頭蓋に囲まれ広がれないため

some unlucky people have to deal with it. We still  have so much to learn about it and until we find a  

呼吸などを制御する脳幹が 圧迫され機能しなくなる

way to treat it, Naegleria fowleri will continue  to be this vague and horrifying thing, hunting  

通常、1週間以内に 患者は死亡する

in puddles and lakes and sometimes pools. Usually  for bacteria. And very occasionally, for people.

このアメーバの感染者の97％が 同じ運命をたどる

- Oh hey, who are you?

ほぼ全てのケースで 感染に気付くころには

It is me, your existential dread!

すでに脳内は苛烈な戦闘中で 手遅れなことがほとんどだ

- Uhm, ok.

有効な治療法が無いばかりか

I'm here to make you question your own  existence and everything you hold dear in life!

疑問がつきない点もある

- Could you not please.

淡水で生活するアメーバが 人間の免疫系に見事に対処できる理由についてだ

Tooooooo late, just look at all these amazing  posters FULL of humbling visualisations like the  

では、この恐るべき殺人アメーバを どれだけ警戒すべきか？

scale of the universe. LOOK! How huge it is and  how small you are! Look at the education edition,  

まあ、そんなに

how it dives deep into the history of evolution or  all these other scientific fields to make you feel  

Naegleria fowleri は明らかに極めて致死的だし 感染は真の恐怖だが

bad for all the stuff you don't know! Or  look at this one, IT GLOWS IN THE DARK!

過去数十年で数百件の報告しかない

- But Dread, these do make me feel good  actually! They do fill me with excitement  

プールで感染するより 溺れる可能性の方が高い

and awe about how amazing our universe is and  I love learning! And look how pretty they are!

鼻の深くに付着するだけでなく

Nooooooooo, I can't persist in  the presence of awe. Graglgrglglg.

しっかり掴まり 防御の第一線を通過する必要もある

If you too want to overcome your existential  dread, make your life beautiful and also support  

結局、Naegleria fowleri は 悪魔でも公衆衛生上の巨大リスクでもない

Kurzgesagt so we can put thousands of hours  into our videos and release them for free,  

ただ毎年、不幸な人々が 相手をさせられている

you can get these and many many  more amazing posters or shirts or  

解明すべき点は多く

so many more things in our shop. We put as  much care into our products as into our videos,  

治療法を見つけるまでは

trying to find something clever or a new angle  that will challenge your perspective while still  

Naegleria fowleri は水たまりや池 たまにプールにいる脅威の怪物のままだ

teaching you the core aspects. It's the best  way to support what we do on this channel.

基本的には細菌への脅威だが 極めて稀に、人間に牙をむくのだ