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Uploaded:2012-04-19
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Hank introduces us to some freaky parasites that use mind control to hijack the brains of their hosts.

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Human parasites episode: http://www.youtube.com/watch?v=ABeBqbBy2Lo

Sources:
http://www.npr.org/2011/10/30/141832947/invasion-of-the-mind-controlling-parasites
http://www.nature.com/nature/journal/v440/n7085/full/440756a.html
http://news.nationalgeographic.com/news/2005/09/0901_050901_wormparasite.html
http://www.radiolab.org/2009/sep/07/the-scratch/
http://wwwnc.cdc.gov/eid/article/9/11/03-0143_article.htm
http://www.redorbit.com/news/health/1657166/researchers_link_parasites_to_schizophrenia/
Images:
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http://farm7.static.flickr.com/6149/5977688562_c903b84c84.jpg
http://en.wikipedia.org/wiki/File:Paragordius_tricuspidatus.jpeg
http://en.wikipedia.org/wiki/File:Spinochordodes_in_Meconema.jpg
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So parasites. Kind of gross, kind of upsetting. Right? You know, they wheedle their way into our bodies, set up camp, basically turn us into a living cafeteria.

I did a whole long episode on parasites. You should watch it. It's super interesting. But what's, you know, more upsetting to me than when they start to, you know, actually eat me, is when they try and take over my brain.

[INTRO]

Or did you not know that there are parasites that can take over your brain? Sorry, well here's the thing. Some parasites aren't content to just set up shop and, like, consume the body of their host. They need their host to do something specific to continue their life cycle.

And because parasites are so crafty, they can do this by, uh, taking over the brains of their hosts. Take for example the green-banded broodsac, a kind of worm that likes to live inside of birds. But, in order to get into a bird, it has to first get into a bird's food. And this is where the snail comes in.

Certain snails love to eat bird poop. You know, to each his own. And bird poop is, you know, where green-banded broodsac larva end up after infecting a bird.

So, a snail strolls by and sees "oh, awesome, some delicious bird crap sitting on a leaf." But little does it know that that poo has a baby little worm larva in it that's going to hijack its brain, turn it into a zombie, and drive its body around like a go-cart.

The worm uses the snail to create this unbelievable scene just to get the attention of the bird. Basically, the worm will drive its zombie snail to a conspicuous location where a bird is sure to see it, and then it jams itself up into the snail's eye tentacle and puts on a laser show, making the snail's head look like a giant, delicious maggot. So a bird eats the snail, and the whole cycle starts over.

But I'll see one of those and raise you a hairworm. These little bastards work their way into insect like grasshoppers through water that the insects are drinking and they live inside of those insects until they are fully grown.

But when it's time for these hairworms to mate, they need to get back into the water. And so you know what it does? It secretes proteins that interfere with the grasshopper's brain chemistry, overrides its entire existence, every fiber of its being, and commands the grasshopper to commit suicide.

It makes the grasshopper jump into the nearest body of water, where it drowns, and the worm is super happy, crawls out of its butthole and goes on to mate with other disgusting butthole worms.

Fortunately for us, not a lot of parasites are able to deal with the marvelously complicated thing that we've got sitting on top of our necks. Oh but there is this one thing.

So there's this protozoan, called toxoplasma gondii, which we're just gonna call toxo for short. Cats poop out the toxo babies, but then cats don't eat cat poop, because that would be gross, unlike dogs. But the things that do eat cat poop, for whatever reason, turn out to be rats. But then the toxo has the problem of how to get from the rat back into a cat. So the toxo interferes with the brain chemistry of the rat, and switches off the little lever that says, "Do not go near cats. Cats will eat you." And instead it tells the rat brain, "You love the cats. You love those kitties. Aren't they--they're so charming and adorable, wouldn't you just like to spoon a cat?"

The first time a rat tries to spoon a cat, you know what happens. It gets chomped. And success!

But here's the thing. People also spend a lot of time around cats. And we're actually pretty similar to rats when it comes to brain chemistry, as upsetting as that might be. And there is research that suggests that the gigantic jump in cases of schizophrenia in the mid to late 19th century occurred at the same time as the gigantic jump in cat ownership.

Indeed, some studies have shown a link between the amount of toxo and the amount of schizophrenia, suggesting that this little jerk might be interfering with human brain chemistry.

But no one is yet saying that this explains the crazy cat lady phenomenon. The jury's still out on that one.

Thank you for watching this episode of SciShow. If you want to subscribe head to youtube.com/scishow where there will be more fascinating episodes, just like the one you that just watched about the science of the world around us and, uh, it will, I promise you, make you a smarter person. Now, if you want to connect with us, ask us questions, or suggest topics, we'll be on Facebook and Twitter and of course in the YouTube comments below.