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If you were around in the '90s, and especially if you lived in the UK,
如果你生活在90年代，尤其是90年代的英国，
you might remember all the panic about mad cow disease.
你可能还记得有关疯牛病的恐慌。
It’s a disorder that's killed thousands of cattle since the '80s and '90s,
自80和90年代这种疾病便导致数千头牛死亡，
and because a version of it can also infect humans, a lot of people were really freaked out.
并且由于这种疾病的一种变体能够感染人类，许多人都非常恐慌。
Today, thanks to safer farming, it probably isn't anything you need to worry about.
而今多亏了安全的养殖，你也可能没有必要再去担心了。
And even though scientists still don't know exactly how it works,
虽然科学家们仍然不清楚疯牛病致病原理，
we can say one thing for sure: Your steak is almost definitely probably not infected.
但有件事我们可以确定：你的牛排几乎绝对不可能被感染。
Mad cow disease is the common name for a condition called Bovine Spongiform Encephalopathy, or BSE.
疯牛病是一种被称为牛绵状脑病或BSE病情的常用名称。
It's a progressive neurological disease that affects cows.
这是一种更加恶化的神经类疾病，能够对牛产生影响。
And over time, it causes severe brain and nervous system damage,
随着时间的流逝，它会引发严重的大脑和神经系统损伤，
which eventually leads to trouble standing and walking, and changes in mood, like increased aggression and nervousness.
最终导致站立和行走问题以及情绪的变化，比如更加强烈的攻击性和神经敏感。
The "spongiform" part of the name just means spongy,
BSE这个名称中的“spongiform”就是海绵体，
because the infection creates a bunch of holes in the cow's brain where its cells should be.
因为感染会在牛大脑内的细胞所在区域形成空洞。
The first two cases of BSE were identified in the UK in 1986,
BSE的头两个病例发生于1986年的英国。
but it takes a really long time for symptoms to show up,
但却是在很久之后才出现症状，
so scientists think the first infections probably date back to the '70s.
因此科学家们认为头一起感染病例可能发生于70年代。
During the outbreak's peak in 1993, almost a thousand new cattle were infected each week,
在1993年该疾病爆发的高峰时期，每周都会有近乎千头牛受感染，
but that number has gone down dramatically since then.
但自那时起，感染数量却急剧下降。
BSE is caused by a bizarre, self-replicating protein called a prion.
BSE是由一种有自复能力的畸形蛋白质引起，这种畸形蛋白质被称为朊病毒。
Other pathogens, like bacteria and viruses, use DNA to make copies of themselves,
其他病原体，如细菌和病毒都是利用DNA进行自我复制，
but a prion is just a deformed version of a normal protein that's found in cell membranes.
但朊病毒只是在细胞膜中发现的普通朊病毒的变体。
Sometimes those proteins can go rogue and get bent out of shape,
有时那些蛋白质我行我素不断变化形态，
but right now, we don't totally understand how or why it happens.
但现在我们无法完全理解其发生的方式和原因。
And when proteins become prions, they can bind to other proteins like them and make them bend in the same way,
当蛋白质变为朊病毒，它们可以绑在其他相似的蛋白质上并以同样的方式使它们弯曲，
and then those messed-up prions corrupt even more proteins, and so on.
然后那些混乱的朊病毒会使更多蛋白质恶化。
Clumps of them collect and spread in the brain and nervous system, eventually causing brain damage.
它们中的一部分会在大脑和神经系统中聚集并传播，最终引发脑损伤。
But that takes a while, so symptoms usually don't show up until years later.
但传播需要一些时间，因此症状直到几年后才会出现。
All of that is terrible, but how BSE got started is almost as horrifying.
所有这些都是可怕的，但是BSE的起因才是最可怕的。
It probably happened because cattle were being fed ground-up meat and bones from sheep and other cows. Ugh!
BSE的发生可能是因为牛被喂食了来自绵羊和其他牛身上的碎肉。呃！
There's another prion disease in sheep called Scrapie,
绵羊身上有另一种朊病毒病——痒病，
and it's possible that scrapie prions may have jumped to cows through their food and caused this whole mess.
痒病朊病毒可能通过所食食物传播到牛体内并引发这场混乱。
But it's also possible BSE just showed up when a random protein folded the wrong way.
但也有可能是因为当一种随机蛋白质错误折叠时，BSE正好出现了。
No matter how it started, the cattle feed only made things worse—
不论起因如何，牛喂养只会让事情变得更加糟糕——
because after cows died of BSE, they were ground up and fed to healthy cows, so the disease kept going.
因为当牛死于BSE后，它们会被碾碎并喂给健康的牛群，因此这种疾病就不断传播。
Unfortunately, a version of the disease can infect people, too.
不幸的是，这种病毒的变体还会感染人类。
The human version of BSE is called variant Creutzfeldt-Jakob Disease, or vCJD, and it's also caused by bent prions.
BSE的人类版被称为变异克雅氏病或vCJD，同样是由于弯曲朊病毒引起。
We don't know for sure that it comes from eating infected cattle,
我们不能确定这是否是因为食用了感染的牛所引起，
but since they're both prion diseases and both outbreaks happened around the same time, most scientists think that's the case.
但是既然它们都是朊蛋白类疾病，并且它们爆发在同一时间，大多数科学家认为这就是由食用感染的牛所引起。
Like with mad cow disease, the symptoms of vCJD can take years to show up, but once they do, things move pretty quickly.
就像疯牛病一样，vCJD的症状可能潜伏好几年，但是症状一旦出现，一切都会发生迅速变化。
Brain degeneration happens in just a few months, with symptoms like trembling, dementia, trouble walking, and eventually a coma.
近几个月内就会发生大脑退化，并伴有颤抖、痴呆、行走困难，最终昏迷等症状。
Since no cure exists yet, patients usually die within a year.
由于目前还没有治愈方法，患者通常会在一年之内死去。
Worldwide, there have been about 230 cases of vCJD, and about 180 of those were in the UK.
世界范围内已有约230起vCJD感染病例，约有180起发生在英国。
The rest were mainly in Europe, and there have been only four cases in the United States, but they were all picked up overseas.
其余的病例主要在欧洲，在美国仅有4起， 但这4起均收录于海外。
The rate at which people have been getting infected has gone way down since the '90s,
自90年代起，人类感染率一直在下降，
but scientists will keep studying it because there are other kinds of Creutzfeldt-Jakob disease not caused by cows.
但是科学家将继续对此的研究，因为还有其他类型的克雅二氏症不是由牛引起的。
Before mad cow disease was a thing, we knew about CJD as a rare condition that could appear if a random protein went bad,
在疯牛病出现之前，我们就知道雅各布病是一种如果随机蛋白质腐败就会消失的罕见疾病，
usually through an inherited mutation, or through medical procedures like transplants.
通常是通过一种遗传突变或通过医疗手段如移植。
Today, we keep the risk of variant CJD low by giving cows safer food and by making sure no nervous system tissue gets into our beef.
今天，我们通过给牛食用安全食物以及确保我们的牛肉中不含神经组织的方式降低变体CJD的风险。
And even though the risk is small, you also can't donate blood in the U.S.
即使风险小，
if you spent too much time in high-risk countries or got a blood transfusion in Europe,
但如果你在高风险国家呆了很长一段时间或是在欧洲输过血，你就不能在美国献血，
because there's a chance prions could be spread through blood, too.
因为这样的话，朊病毒就有机会通过血液传播。
Mainly, it's those new farming practices that have really helped get the disease under control,
基本上来讲，正是因为那些新的养殖方式才使得这种疾病得以控制，
and in 2016, there were no new reports of BSE in cows in the UK for the first time since the outbreak started.
2016年，自疯牛病爆发以来，英国第一次未出现BSE的新报告。
Which is both exciting and a relief.
这样的情势即令人兴奋也像是一种安慰。
Also, because mad cow disease is transmitted through nervous system tissue,
同样，因为疯牛病通过神经组织传播，
there's no evidence you can get it from milk or the meat used to make things like hamburgers and steak.
没有证据证明你会由于饮用牛奶或食用汉堡和牛排而感染。
So your roast beef is not out to get you, which is always good to know.
所以你的烤牛肉不会吃了你，知道这一点总是有好处的。
Thanks for watching this episode of SciShow, and special thanks to Patreon patron Scott Sorrell for asking us about mad cow disease!
谢谢收看本期科学秀，特别感谢Patreon观众Scott Sorrell的提问！
If you'd like to submit your questions or just support the show, you can do so at patreon.com/scishow.
如果你想提问或是支持科学秀，请登录patreon.com/scishow。
