In fact, if someone with measles coughs in an elevator, 90% of the people who use that

實際上，如果患有麻疹的人在電梯中咳嗽，那麼在使用該電梯的人中

elevator after will catch the disease.

有 90％ 會感染到麻疹。

Unless of course you've been vaccinated.

當然，除非你已經接種過了疫苗。

Then you'll be completely fine.

那你就不會有事。

This is the measles virus, it's been around for thousands of years and has been responsible

這是麻疹病毒，已經存在了數千年，並造成了

for the deaths of millions of people.

數百萬人的死亡。

Now, on the surface, measles symptoms seem fairly innocuous.

現在，從表面上看，麻疹產生的症狀似乎是無害的。

But the real damage, the damage that can lead to death, happens on a cellular level.

但是真正的傷害，可能導致死亡的傷害，是發生在細胞上。

Hi I'm Roberto Cattaneo.

嗨，我是 Roberto Cattaneo 。

I'm a Doctor of Philosophy and Professor of Molecular Biology at the Mayo Clinic.

我是梅奧醫學中心的博士，及分子生物學教授。

I'm studying the measles virus since about 35 years.

我研究麻疹病毒大約已經 35 年了。

Measles uses the trachea as a trampoline.

麻疹把氣管當成跳板。

It is in the ideal position in the body to get expelled and to get aerosolized dispersed

氣管是身體中將病毒排出體外最理想的位置，它將病毒以小分子霧狀方式

in the air in small particles very efficiently.

有效地散播至空氣中。

When someone with measles coughs or sneezes, these droplets contain the measles virus,

當患有麻疹的人咳嗽或打噴嚏時，這些飛沫中會含有麻疹病毒

and because measles is a respiratory disease, all someone needs to do is breathe in that

並且由於麻疹是一種呼吸系統疾病，因此人們只要吸入被病毒感染的空氣

infected air in order to contract measles.

就會染上麻疹。

Unless, of course, they've been vaccinated.

當然，除非他們已經接種了疫苗。

When the measles virus reaches the lungs, it is met by a type of white blood cell called a macrophage.

當麻疹病毒到達肺部時，會遇到一種叫做巨噬細胞的白血球。

Usually, macrophages seek out and destroy dangerous pathogens like viruses.

通常，巨噬細胞會發現並消滅，像是病毒之類的危險病原體。

But the measles virus tricks the macrophage into not seeing it as a danger and instead,

但是麻疹病毒，會誘使巨噬細胞誤認為它是沒有危險性的

safely transports the virus into the body's lymph nodes.

反而將它安全地運送至人體的淋巴結。

It's here that the virus begins to replicate and spread throughout the entire lymphatic system.

就在這裡，病毒開始複製並傳染至整個淋巴系統。

Yea, I mean the macrophages thinks to have a system in which they basically get rid of the virus

是的，我的意思是說，巨噬細胞基本上有一套機制可以消滅病毒

And measles can stay there.

但是麻疹病毒卻可以在那裡存活。

So not only it is invisible but it begins to make damage to these cells.

因此，它不僅像是隱形的，而且還開始對這些巨噬細胞造成損害。

The task of these cells is also to go out and fight infection,

這些細胞具有抵抗外來感染的任務

but instead of fighting infection, they go out with the virus and distribute it to the body.

但它們不但沒有抵抗病毒感染，反而將其傳播到身體各部位。

Now, as the virus starts to spread, it enters immune cells that express a protein named

現在，隨著病毒開始傳播，它侵入至免疫細胞裡稱為

SLAM.

SLAM 的蛋白質受體。

These cells are “memory” immune cells, meaning that they remember other pathogens

這些細胞是有「記憶」能力的免疫細胞，這意味著它們會記住

that previously infected the host.

先前感染過宿主的其他病原體。

Measles attacks and kills these SLAM-expressing memory cells and once those memories of past

麻疹病毒會攻擊並殺死這些記憶細胞，一旦過去感染的記憶被清除

infections are erased, the body will be in a much weaker position to fight off future infections

人體對於未來被感染的抵抗力就會變弱了。

This is why measles is so deadly.

這就是為什麼麻疹如此致命的原因。

But even though the virus has tricked your immune system to helping it, that doesn't

但是，即使麻疹病毒欺騙了你的免疫系統，也並不表示

mean your immune system has given up.

你的免疫系統已經無效。

Well, at some point the immune system will notice and will secrete cytokines and attract other immune cells.

在某個時候，免疫系統會反應而分泌出細胞激素，並引起其他免疫細胞的注意。

So at some point the enemy will be identified and taken care of.

在此同時，病毒就會被識別出來而被消滅。

But for the viruses in fact it is only necessary to get out of the host and find a new host.

但是實際上，對於病毒而言，它只需要脫離原宿主，去找一個新宿主就可以繼續存活。

So it's in fact better not to kill the host.

因此，病毒實際上最好不要殺死宿主 (它才能繼續被散播出去)。

That's right, it's in the best interest of the virus not to kill you, that's some other diseases job.

對的，不將你殺死，才是對這種病毒最有利的，殺死宿主是其他疾病的事。

The job of the measles virus is to find a new host, which brings us to another protein

麻疹病毒的任務既是尋找新的宿主，我們就必需提到該病毒入侵的

the virus expresses: nectin4.

另一種蛋白質受體：nectin4。

And we discovered nectin4 as the epithelial receptor or host exit receptor for measles virus.

我們發現 nectin4 是麻疹病毒入侵上皮細胞的受體或宿主出口受體。

As measles spreads throughout the body, it also enters cells that express the protein nectin4.

隨著麻疹擴散到全身，病毒也入侵細胞的 nectin 4 蛋白質受體。

This protein is expressed very preferentially in the trachea.

這種蛋白質在氣管中特別顯著。

And the more the virusit replicates in the trachea, the more cells it kills there.

病毒在氣管中複製的越多，被殺死的細胞就越多。

This dead cell build up actually causes the human host to cough or sneeze, helping spread

被殺死的細胞屍體不斷堆積，就會造成人類宿主咳嗽或打噴嚏，這樣就就助長

it into a new human host, bringing us right back to where we started.

將病毒傳播到新的人類宿主中，從而又開始一個另一個的傳染循環。

Now, the good news is that once you get the measles, your body learns how to defeat it

現在，好消息是，一旦你得了麻疹，你的身體學會了如何戰勝它

and you probably won't get it again.

那你可能就不會被再次感染了。

This is similar to how the vaccine works, but the difference is you're given a weaker

這與疫苗的原理是一樣的，區別在於疫苗的劑量較低

dose, so you can become immune without getting sick or damaging your immune cells.

因此你既可以免疫又不致生病或損壞免疫細胞。

So the vaccine causes the host to remain immune to measles we think for life long or almost life long time.

因此，麻疹疫苗可使人類對麻疹有終身或近乎終身的免疫功效。

And without measles, other diseases, the ones that actually do the killing, have gone down.

少了麻疹，其他疾病，也就是真正足以致死的疾病，都已减少了。

Basically the number of hospitalization has been reduced considerably sometimes to about

基本上，一些因其他傳染病而住院的人數已大大減少

half for several different infectious diseases.

有時甚至減少了大約一半。

So, if you haven't been vaccinated...

因此，如果你尚未接種疫苗...

Yea, the vaccine works beautifully.

沒錯，麻疹疫苗的效果很好。

maybe think about it?

也許你願意考慮一下？

Measles may be the enemy of the immune system, but researchers, including Dr Cattaneo, are

麻疹可能是免疫系統的敵人，但包括 Cattaneo 博士在內的研究人員

working on ways to alter the measles virus so it kills cancer cells.

正在研究用對付麻疹病毒方法，來殺死癌細胞。

For me, a reason to continue study measles is to make it into a friend, making an old

對我來說，繼續研究麻疹的一個原因，是想把它變為朋友

enemy into a new friend by modifying it genetically.

通過基因改造，把原來的敵人變成新的朋友。