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《科学秀》由Brilliant.org赞助播出。
If your summer has ever included cooling off with a nice swim in a lake,
如果你夏天去湖里游泳的话，
you might be acquainted with something called swimmer's itch.
你或许会了解被称为游泳者瘙痒症的东西。
These itchy red bumps appear on the exposed parts of your skin after you take a dip in a lake or pond,
去湖里或池塘里游完泳上来，这些痒痒的红疹就会出现在你的皮肤上，
and they can last for a week or more. But swimmer's itch is more than just an annoying rash
这些红疹会持续一周。但是游泳者瘙痒症并不仅仅是这些恼人的皮疹
it's actually caused by parasites that burrow into your skin and then die there. Yeah. Ew.
事实上它是由钻入并死在你皮肤里边的寄生虫引起的。没错，很恶心。
The culprits are tiny worms called schistosomes.
罪魁祸首是一种被称为血吸虫的小蠕虫。
Each schistosome species specializes in a specific bird or mammal host.
每种血吸虫都专门以某种鸟类或哺乳动物为寄主。
Some schistosome species target humans, causing a debilitating disease called schistosomiasis.
一些血吸虫以人类为目标，引起血吸虫病。
But the ones that cause swimmer's itch aren't after you
但是那些引起游泳者瘙痒症的血吸虫并不是以你为目标
they're part of a different group of species whose hosts include ducks, geese, muskrats, and raccoons.
它们是一种不同的种类，它们的寄主包括鸭子、鹅、麝鼠以及浣熊。
That itchy rash is what happens when one of these schistosome larvae makes a mistake.
当其中一种血吸虫幼虫出错时，就会发生这种痒痒的皮疹。
Adult parasites live in their host's blood, and when they lay eggs, the host eventually poops them out.
成年寄生虫生活在寄主的血液里，它们产卵时，寄主最终会把它们排出来。
With a little luck, the eggs end up in water, where they hatch into larvae
比较幸运的卵会流入水中，孵化成幼虫
that swim around in search of the aquatic snails that they need to infect to complete the next stage of their life cycle.
在水中游荡寻找水生螺，以便完成生命周期的下一个阶段。
The baby schistosomes continue to multiply and develop inside the snail,
幼虫继续繁殖并在螺中成长，
and eventually the infected snail releases a second type of larvae called cercariae into the water.
最终被感染的螺往水中释放第二类幼虫—摇尾幼虫。
This is where swimmer's itch gets its technical name, cercarial dermatitis.
因此游泳者瘙痒症得名尾蚴性皮炎。
These little guys, each less than a millimeter long, head out to look for a member of their original host species to start the cycle all over again.
这些不超过一毫米长的小家伙，探出头寻找它们的原寄主再次开始新的周期。
You'd think it would be easy to tell the difference between a human and a muskrat or goose or whatever,
你或许认为辨别人类、麝鼠或鹅很简单，
but sometimes the cercariae mess up and burrow into a human swimmer's skin. It's a fatal mistake.
但是有时，摇尾幼虫就会弄错，然后钻进人类游泳者的皮肤中。这是一个致命的错误。
They can't develop there, and so they die.
它们无法在那里生长，所以它们会死掉。
And because dead baby parasites are definitely not something that's supposed to be in your body,
因为死掉的寄生虫宝宝绝对是不应该出现在你身体里的东西，
they trigger an allergic reaction as they break down. That's what all the itching and redness is from.
它们会触发一种过敏反应，因此引发瘙痒和红肿。
Because it's an allergic reaction, some people are more sensitive than others
因为这是一种过敏反应，所以一些人对这些更为敏感
it just depends on how strongly your immune system responds.
这取决于免疫系统的反应强度。
And if you're exposed to swimmer's itch over and over again, you can actually become more sensitive to it over time.
如果你一次又一次出现游泳者瘙痒症，那么你真的会对它更加敏感。
You're most likely to get swimmer's itch in freshwater,
在淡水中更有可能出现游泳者瘙痒症，
but it's possible to get it in salt water too, so even at the ocean you're not completely safe.
但是在盐水中也有可能，因此即便在海洋中，你也不是绝对安全的。
To keep your risk small, towel off or shower as soon as you get out of the water,
为了降低危险，一上岸就拿毛巾擦擦或是洗个澡，
and don't do anything to attract birds that may host schistosomes to the area.
不要做任何吸引鸟类的事情，它们可能携带吸血虫。
That's right -- no more feeding the ducks.
没错—也别再喂鸭子了。
It's a small price to pay to avoid parasites dying a slow, itchy death under your skin.
这是避免寄生虫在你皮肤下慢慢痒痒地死去所付出的小代价。
If you don't want to take your chances at the beach, maybe a mathematical game of chance is more your style.
如果你不想在沙滩上冒险，或许数学机会对策是你的菜。
This course on Brilliant.org will sharpen your math skills while helping you master probability.
Brilliant.org的这个课程将锻炼你的数学技巧，帮助你掌握几率学。
Thinking about parasites dying under human skin really put me in the headspace for the "Survive this Chapter" part.
想到寄生虫在人类皮肤下死亡真的让我想到了Survive this Chapter。
You have to avoid eating a poisoned apple and all kinds of dangerous situations to progress onto the next challenge.
你要避免吃掉毒苹果以及避免各种危险才能进入下一关。
It's fun, and I learned a lot, and best of all, you're actually completely safe the whole time.
很有趣，我也学到了很多，最棒的是，完全安全。
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点击Brilliant.org/SciShow
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前200名通过连接注册的用户将获得订阅年费八折优惠。
