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寄生虫是怎么霸占和指挥我们的神经的 – 译学馆
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寄生虫是怎么霸占和指挥我们的神经的

How Parasites Commandeer and Change Our Neurocircuits | Kathleen McAuliffe

你的神经是否被猫的寄生虫占领?
我们都知道 寄生虫能让我们生病吸取我们的营养
We know that parasites can make us sick, of course, and siphon off our nutrients, but
但令人惊讶的是 他们(寄生虫)中的一些 事实上可能是一个很大的数字
it’s very surprising to hear that some of them, in fact there may be a large number,
至少有一百 此时此刻操纵着宿主的行为
at least a hundred are known about at this point in time manipulate the behavior of their host
来扩大他们的传播
in order to enhance their own transmission.
能理解这个现象的最好方式 我认为需要一个例子
And the best way to understand this phenomenon I think is with an example.
猫身上有一种寄生虫叫做 刚地弓形虫简称弓形虫
And one is a cat parasite called Toxoplasma Gondii or just Toxoplasma for short.
在阅读相关科学研究时 我第一次了解到这种寄生虫的操纵行为
I first learned about this parasitic manipulation while just reading about scientific research
我遇到的一个研究显示 被这种寄生虫感染的啮齿动物
and I came across a study that showed that rodents that are infected with this parasite,
他们可以从地面沾染这种寄生虫
they can pick up the parasite from the ground.
猫从粪便中排出这种寄生虫 因为啮齿动物在四周清扫就会沾染弓形虫
Cats defecate this parasite so rodents as they arescavenging around can pick up the parasite
然后弓形虫就会侵入啮齿动物的大脑操纵着动物的神经回路
and it then invades their brain and it actuallytinkers with the animal’s neural circuits
这种改变会使啮齿动物被猫尿所吸引
in such a fashion that it makes it attracted to the scent of cat urine.
我所说的“吸引”指的是性吸引
And when I say attracted I mean sexually attracted.
猫尿的气味引起啮齿动物的性冲动因此他们会接近猫
The rodents become sexually aroused by the scent of cat urine so they approach and
不必说 他们这是不想活了他们很快就会死在猫的胃里
they are
不必说 他们这是不想活了他们很快就会死在猫的胃里
and needless to say they’re not long for this world and they soon end up in the belly of a cat
猫的胃是弓形虫进行有性繁殖的唯一场所
and that’s the only place where this parasite can sexually replicate.
这是它的小诡计
So that’s its little trick.
它同时也做着其他许多事情
And it does many other things as well.
例如 弓形虫可以转移到睾丸
For example, the same parasite goes to the testicles and
促进性激素睾酮的释放
jacks up production of the sex hormone testosterone.
在雌性中 还没有人知道 它可以
In females, by means nobody’s figured out yet, it can
增加性激素孕酮的水平
increase the level of the sexhormone progesterone.
在所有案例中 这些变化会使啮齿动物更加勇猛
And in both cases these changes make the rodent more embolden
可以说 导致他们降低警惕 愚蠢地对猫采取行动
and cause the rodent to sort of lower its guard and to act in foolish ways around cats.
关于弓形虫的其他诡计 另一个例子是
So that’s yet another example of other tricks it has
它可以返回猫的胃
for getting back into the belly of a cat.
弓形虫也可以感染我们
This parasite can also infect us.
我们感染它的途径之一是 通过换猫砂盒
One of the ways we can get it is changing a cat’s litter box.
在当前的医学思维中
And the current thinking in medicine is that
弓形虫主要对胎儿发育构成威胁
the parasite it mainly poses a threat to a developing fetus
它可以在胎儿发育过程中损伤神经系统甚至是导致失明
and can harm the developing baby’s nervous system or even cause blindness.
众所周知 其也对免疫能力低下人群构成威胁
And it’s also well known to be a threat to people who are immuno-compromised, so for
比如 接受器官移植或进行化疗的人群
example, people who have received transplanted organs or being treated with chemotherapy.
目前认为对于大多数健康人群而言
And it’s still assumed that for most healthy people
一旦寄生虫进入大脑 并不会造成威胁
it poses no threat that once the pararsite get inside the brain, and it just
它只是在神经内待着不动不会产生任何问题
hunkers down inside neurons never again to cause any problems.
但是现在 有几个欧洲或者美国实验室
But there’s now several labs, bothin Europe and the United States
有所质疑
that are challenging that dogma.
他们发现的大量证据表明 对于一小部分人群而言
And they have uncovered a lot of evidence that for a small percentage of people the
隐性感染确实会产生不良后果
dormant infection may indeed have adverse consequences.
还没有人确证是多少比例的人群
Nobody yet has a handle on what percentage
但是约有20%的美国人都有寄生虫感染
but about 20 percent of all Americans are infected with the parasite.
所以人们猜测 我们只是在讨论很小一部分的人群
So people’s guess is that we’re only talking about a small percentage of people who have
他们会出现这些不良反应
these adverse responses.
但是除此之外 寄生虫也与精神疾病相关
But among other things it’s a link to mental illness.
所以 例如精神分裂患者 他们的抗寄生虫抗原
So people with schizophrenia, for example, they are two to three times more likely to
是正常人的两到三倍
have antigens against the parasite.
寄生虫也与躁狂抑郁症和自杀相关
It’s also been linked to manic depression and it’s been linked to suicide.
在一个涉及欧洲22个国家的研究中 研究者发现
There was actually a study done in 22 nations in Europe and the researchers found that suicide
每个国家的寄生虫患病率与自杀的增多成正比
increased in direct proportion to the prevalence of the parasite in each country.
已发现寄生虫与危险驾驶有关
And it’s been a link to dangerous driving.
几个不同国家做的研究中显示 寄生虫测试阳性者
Several studies in a few different countries have shown that people who test positive for
更容易出现车祸
the parasite are more likely to be in car accidents.
有个理论认为 没有人确切知道出现这种关系的原因
So one theory, nobody knows for sure why what the reason for this association is, but one
还有人推测 就像啮齿动物会降低警惕 行为自大一样
theory is that just as rodents lower their guard behave in a cocky way maybe people behind
可能开车的人也没有足够警惕
the wheel of a car are less vigilant.
也有研究表明 被感染的人相对有较长的反应时间
Or there’s also research that shows that infected people have slightly slower reaction times
所以这也可能是影响他们驾驶的另一个因素
so that’s perhaps another factor that may influence their driving.
需要强调的是 这些都是相关性研究但是因为科学家们已经了解到
I should emphasize these are all correlational studies, but as scientists have learned more
寄生虫对啮齿动物的大脑所造成的影响使得他们认为一些说法是合理的
about what this parasite does to the rodent brain it does make them think it’s plausible
即 隐性感染确实会一些人带来麻烦
that the dormant infection is indeed causing trouble for some individuals.
自然界中有许多令人惊叹的关于寄生虫操纵行为的例子
There are many amazing examples of parasites in nature that are manipulating behavior.
我最喜欢的一个例子是 寄生藤壶
One of my favorite examples is a parasitic barnacle.
暂停任何对藤壶先入为主的观念
You know, suspend any preconceived notions you have about barnacles
因为藤壶突破传统
because this of barnacle is very iconoclastic;
它没有壳 也不会附着在同类或石头上
it doesn’t have a shell; it doesn’t attach to the sides of peers or to rocks.
它在生命周期中的某个阶段是自由生存的那个阶段中 它可以降落在螃蟹上
It’s free-living during one phase of its lifecycle, which at that point it can alight on a crab
然后将它的一小从细胞注给螃蟹
and inject a small clump of its cells into the crab.
那些细胞生长成一团根状结构
And those cells then grow intoa tangle of root like structures
这些根将螃蟹的内部器官都缠绕起来甚至最终杀灭了螃蟹的所有细胞
and these roots wrap around all the crab’s internalorgans and eventually even sterilize the crab.
在螃蟹的腹底部通常会长有一个孵育后代的育儿袋
And where the crab would normally grow a broodpouch on the bottom of its belly to incubate it’s young,
藤壶会把蟹都推出去然后长出一个它自己的育儿袋
the parasitic barnacle pushes out of the craband grows a brood pouch of its own.
从那一刻起 这只螃蟹的存在就只是为了给寄生虫提供饲料
And from that moment forward this crab lives and exists solely to feed the parasite and
以及照顾寄生虫的后代
to take care of it’s young.
它搅动育儿袋附近富含氧气的水
It waffs oxygen rich water around the brood pouch to
以使寄生虫的后代能充分接触氧气
keep the parasite’s offspring well oxygenated.
然后当寄生虫的后代即将出生时螃蟹会去往更深处的水域
And then when its young are ready to be born the crab then goes into deeper water
上下摆动 将寄生虫幼体释放入水流中
and bobs up and down and releases the parasite’s babies into the currents
随之去往世界各地 去掌控更多的螃蟹的身心
where they then go off into the world only to commandeer the minds and bodies of more crabs.
我的意思是 对我来说 这是最接近现实生活的盗尸者
I mean to me this is the closest real life thing to a body snatcher,
常在科幻小说中出现的盗尸者
science fiction’s idea of a body snatcher.
我甚至叫他们机器蟹
Because I even call them robocrabs
因为他们基本上像是一个被寄生藤壶控制的两栖机器人
because they are basically like an amphibious robot controlled by this parasitic barnacle.
自然界中还有许多很好的例子
There is many other great examples in nature.
另一个给我留下深刻印象的是 寄生蜂
Another one that I think is very impressive is a parasitic wasp
它会抓住圆蛛 贴上蜘蛛腹部的卵
and it will grab hold of an Orb spider and attach its egg to the abdomen of the spider.
然后当卵孵化出幼虫 幼虫会分泌出各种化学物质
And then as this egg hatches into a larva the larva secretes all kinds of chemicals
这些化学物可以有效控制蜘蛛建造它的温床
that effectively instruct the spider to build it a nursery.
因此蜘蛛放弃了它正常的编织模式停止了那种经典的圆形图案
So the spider abandons its normal weaving pattern, it stops making that sort of classic circular motif
而是为寄生蜂幼虫建造了一种吊床似的结构
and instead creates a sort of hammock like structure for the parasitic wasp’s larva
幼虫会附着在这个网的中心
and the larva actually attach to the center of this net.
蜘蛛甚至会在寄生虫周围编织一种装饰性的图案
And the spider even weaves a sort of decorative motif around the parasite
以保护它免受敌人的危害
to protect it from its own enemies.
基本上可以认为
It’s something even as think fundamental as
是这些寄生蜂从根本上改变了蜘蛛的编织方式
how a spider weaves can be radically changed by these parasitic wasps .
同时他们中至少有一打 都导致了完全不同种类的网的产生
And there’s at least a dozen of them and they all induce completely different kinds of webs.
因此 关于寄生虫的操纵能力 我认为这个真的是一个令人印象极其深刻的例子
So that’s one example of I think a really impressive example of a parasitic manipulation.
有一种可以进入鳉鱼体内的寄生蠕虫(鳉鱼在加利福尼亚esrines很常见)
There is a parasitic worm that gets into killifish, it’s a very common fish found in California esrines,
寄生蠕虫会侵入鱼的大脑导致鱼上升到水面
and it invades the fish’s brain and the fish as a result rise to the surface
鱼身翻转 基本上不再使用他们的鳍当捕食的鸟类在上空盘旋时
and flip over on their sides and basically waive their fins at predatory birds that are circling overhead,
不必说 鸟类会俯冲下来吃掉这些鱼
which that needless to say swoop down and eat the fish.
这种被寄生的鱼有很多很多 它们更容易被鸟捉住
And the parasitized fish are much, much more likely to be caught by birds,
被捉住的次数至少是正常鱼类的四倍
at least four times more likely to be caught.
而寄生蠕虫所做的似乎是 作用于大脑的一部分
And what the parasitic worm appears to do is it acts on parts of the brain
通过血清素,神经递质血清素控制大脑
that are controlled by serotonin, the neurotransmitter serotonin.
除非被感染的鱼更加成熟 否则从各方面看来它们都是正常而健康的
And the infected fish seem normal and healthy in every single way mellow.
他们就像是吃了百忧解的鱼(百忧解治疗精神抑郁)
They’re like a fish on Prozac.
这就是寄生虫如何进行它的操纵行为的
So that’s how that manipulation works.
另外一种操纵行为 想起来就令我发抖 它来自真菌
Another manipulation that actually makes me shudder when I even think about it, it’s a fungus.
其发生在蚂蚁身上 当蚂蚁行走在森林地面上时
And what happens is ants as they’re on the forest floor
这种真菌居无定所
and there is nothing domicile about this fungus
因为一旦它沾染在蚂蚁身上
because as soon as it attaches to the ant
它就会钻入蚂蚁体内 开始快速生长
it burrows into the ant and it starts rapidly growing.
当它在做这些事的时候 他还会命令蚂蚁
And as it’s doing this it instructs the ant
去往植物在西北面的那部分
to go to the northwestern a part of plant
然后这种真菌
and then this fungus,
这是让我毛骨悚然的一部分像是从蚂蚁头部长出的豆芽
and this is the part of the creeps me out, like sprouts from the ant’s head
它长出这么长的枝干
and it grows this long stock.
在这个枝干的尖端是这种真菌的子实体然后子实体会爆裂开来
And at the tip of the stock is this fruiting body that then explodes
播撒孢子在更多的蚂蚁身上而他们正行走在下面的森林大地上
and rains spores down on more ants that are walking along the forest floor below.

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