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MLA Full: "Terrifying Parasites Inside the Human Body." YouTube, uploaded by SciShow, 6 May 2012,
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APA Full: SciShow. (2012, May 6). Terrifying Parasites Inside the Human Body [Video]. YouTube.
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Chicago Full: SciShow, "Terrifying Parasites Inside the Human Body.", May 6, 2012, YouTube, 09:05,
WARNING! This video may freak you out. While some parasites can actually do good in the human body, many do not. In fact, some of the bad ones are downright terrifying. Join Hank Green for a creepy look into the world of parasites—but you've been warned!

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References for this episode can be found in the Google document here:
Hank: We're pretty used to considering our bodies to be our property. You're born with this body; you can feed it and exercise it, and clothe it however you would like. You could make it smarter or dumber in any way you see fit. Because this is my body, right? Well, yeah, technically, I mean, you own your body the way that you own your house except you can't sell it... at least legally. But it turns out you are not the only resident of your body. Let's just say that you have some tenants. And like all tenants, there are some that, ya know, mow the lawn, and shovel the side walks, and fix the leaky sinks for you. And then you have the ones who are cooking meth in the bonus room and blowing up your garage with fireworks.

[intro music]

So welcome to this video: it's all about the stuff that lives inside you. Look on the bright side, though. If you Googled human parasites you'd see all kinds of pictures you do not want to see, so this is much better a way of being introduced to the topic. So consider it a gift from me. I'm gonna tell you all stuff that you need to know without telling you about much of the stuff that you really don't want to know about, and probably isn't gonna happen to you anyway. Namely the *"censored" beeps* being *"censored" beeps* noses and *"censored" beeps* and s-*"censored" beeps* that they *"censored" beeps*. These are things I've seen, you guys. And they can't be unseen.

So, "parasite." That's a strong word. Technically a parasite is any organism that makes its living off of another organism. And sometimes they're bad, and sometimes they're not. Parasitism is a pretty clever strategy. They just sort of sneak in, they set up camp inside of a body, and then they can devour it from the inside out. Or they might not do any significant harm at all or they might even help their host animal. There are many animals living inside of me right now that are actually helping me live a happy, healthy life, and there are also a bunch that I just don't notice and are completely unobtrusive. So I'm going to talk about these good guys first, and then a little later on I'm going to scare the adenoids out of your face by talking about those supervillian parasites that you do not want.

So, animals that live, you know inside of another animal but actually help them, those are called "mutualistic symbiotic relationships." And that's roughly the relationship that we have with the one hundred trillion microbes that are living inside of us at any given moment. So, one hundred trillion - hard to really wrap your mind around that number. As scale: number of cells that you have with YOUR DNA in them: about ten trillion. I'm gonna say this again for you. There are TEN times more bacteria cells in your body than "you" cells. Do your best not to let this freak you out, 'cause those are really really important littler animals living in you, and they make your life WAY BETTER. Some scientists are going so far as to call this the "human microbiome." We're our own biome! So much so that some scientists have gone so far as to name this human microbiome -- that is, the ecosystem of animals that lives inside of us -- our "forgotten organ."

So, what are these things doing to earn their keep? Well, I'm glad you asked that. They kill harmful bacteria in our noses, they form a protective coating on our skin, and the vast majority of them live in our intestines, doing really useful stuff, like helping us break down the food that we can't digest by ourselves, making vitamins biologically available to us, teaching our immune systems not to freak the frick out over stuff that doesn't matter, and killing off the harmful bacteria that often find their way into our guts. Without them, our lives would be miserable. And I'm gonna tell you HOW miserable, I'm just gonna say that adult diapers would be involved. They're so important that doctors are now diagnosing people with bad gut bacteria. And they're putting GOOD gut bacteria into the people through what's called "fecal transplants," which is exactly what it sounds like. (I talk about it more on my "Obesity" video.)

But not all of the animals that live inside us are super-good-awesome animals. Some of them are just... "meh." We provide a lot of food and transportation and lodging for a lot of animals that do basically do absolutely nothing to us. This is called "commensal symbiosis," when one of the participants benefits, and the other one... it doesn't care. An example of this being the eyelash mite or follicle mite that basically lives anywhere that there's hair on your face. Basically these tiny little arthropods just hang onto the base of your hair follicle and eat the oils that are secreted by your sebaceous glands. And that might seem gross and sort of not cool to you, but it's not really affecting you in any way, so I suggest you just deal with it. Besides, you're gonna have to save your big freak out guns for where we're headed to right now.

Be Advised: The rest of this video is moderately-gross and may not be suitable for all audiences, especially those who suffer from delusional parasitosis, which, by the way, is a real thing.

Objectively, parasites are pretty awesome. I mean, they're tiny, generally, but they're scheming, and they're clever, and they can take down an animal much much much much much much bigger than it. Parasites that feed on humans -- the bad sort of parasites -- can be organized into a few different groups. We have the protozoans, the worms, the crawly bugs, and category number four: freaky stuff.

So let's start with the protozoans. Now, protozoa, which you may have heard of, are one-celled organisms, a lot of which can kind of move around on their own and get into the host through drinking contaminated water, or through the saliva of a tick or a mosquito that bites you, etc. And once these bad guys are in your gut or your blood or whatever, their single mission is to take you down. Take, for instance, Naegleria fowleri, also known as the brain-eating amoeba. This guy is found in bodies of fresh water that stay pretty warm all year. And this is why I live in Montana. So basically this little guy spots you swimming around in some tepid lake or river somewhere, crawls over to you, and wiggles it's way right up your nose. From there, it works up to the olfactory bulbs of your fore-brain and starts to feed on your nerve tissue. And then, your brain starts to swell up and then 98% of the time... you die. In 2011 two people died because they were using contaminated water to irrigate their sinuses with Neti Pots, so always remember to boil your Neti Pot water, especially if you live in Louisiana. Anyway, there are a bunch of other diseases that you've probably heard of that are caused by a parasitic amoeba: African sleeping sickness, giardia, malaria, toxoplasmosis.

And this bring us to the second type of parasites: the worms, which are arguably the worst. These are the ones which I highly recommend you DO NOT GOOGLE because parasitic worms are in it to win it! And when I say "win it," I mean "breed so many worms that they fill your whole body up and start coming out your nose or your butt." So, good news! If you live in the developed world and you have, like, power outlets and hot water and an internet connection, you probably don't have any chance of getting any of these worms. But many people in the developing world have to deal with these kinds of things every single day because they don't have access to clean food and water like we do. They're more likely, because of lack of plumbing, to be in more contact with human feces, and they live in a part of the world where a mosquito bite can lead to Elephantiasis. Ah yea, Elephantiasis, or Lymphatic Filariasis, an infectious tropical disease caused by parasitic round worms that are passed from person to person through mosquitoes. The worms can cause unbelievably horrifying amounts of swelling in the legs, arms, breasts, and genitals of their victims. Elephantiasis, it turns out, is one of the leading causes of disability worldwide.

So the next type of parasite, of course, is the crawly bugs, which is my classification for parasites that feed on you from the outside, like your bed bugs, or your scabies, or your body lice, or your genital crabs, that kind of thing. Now, in my opinion, these things are way better than the worms or the protozoa because they just-- they're way less likely to kill you. But they ARE pretty gross. In fact, just talking about them makes me feel like there's things crawling on me. And this is where the word delusional parasitosis comes in, that disease which has nothing to do with parasites except that you think you have them because you've been hearing about them and it makes your skin crawl.

And finally, we have number four, our last category of parasites: the freaky ones. And there are lots of other kinds of parasites as well, of course, like the botfly, which lays its eggs under your skin where they hatch and then feed on you until they're ready to... erupt, as it were. And  then there's the candiru, a tiny parasitic catfish that lives in the Amazon River and loves the smell of urine. If you're in the Amazon River and peeing, which I suggest you do not do, the candiru may sniff you out, swim up your urethra and camp out there until it is surgically removed. HNNNNNNGGGGGG

And these, my friends, are the tenants of your body. And I hope that you have them, the good ones at least, and the bad ones: well, let's just... get 'em away from us. Congratulations on becoming a smarter person! There are citations for this episode in the description if you would like to have them and read more about this. I question why you would want to, but it's very interesting. You can, as always, connect with us on Facebook and Twitter, ask us questions, suggest topics for us, and of course, down in the YouTube comments below.