Michael Mosley: Infested! Living with Parasites


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Michael Mosley: Infested! Living with Parasites

Dr Michael Mosley explores the bizarre and fascinating world of parasites by turning his body into a living laboratory and deliberately infesting himself with them.


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The tapeworm.

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It's one of nature's most fascinating parasites.

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There are thousands of different kinds of tapeworm,

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each evolved to live in a different host species.

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And there are several species of tapeworm that live in humans,

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including one called Taenia saginata.

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Like many parasites, it has a complicated life cycle,

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which involves passing through more than one species.

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So imagine you're in rural Kenya

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and you've got a great big tapeworm inside you.

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This tapeworm is producing eggs.

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One day, you go down to a field and you excrete there,

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and you contaminate the grass.

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Then along comes a poor unfortunate cow who eats that grass.

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Along with grass, the cow eats the tapeworm eggs,

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which hatch into larvae and then enter the cow's bloodstream...

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..spreads through the blood to the muscle,

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perhaps the shoulders or the tongue,

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and there it forms a really tough cyst.

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And it hangs around, just waiting for the next stage,

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which is for the cow to be eaten by a human.

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The beef tapeworm can only grow to adulthood inside a human,

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and for that reason, it's hard to study.

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So I've decided to infest myself,

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as my contribution to research into these shy, retiring creatures.

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So I need to find infected beef.

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But in Britain, it's extremely unlikely

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you'll find a contaminated cow,

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which is why I've come to Kenya.

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With the help of a local meat inspector,

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we found some infected meat.

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Then we cut three cysts out of the meat,

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ready for me to swallow.

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Cheers.

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It's like jumping off a cliff. Here we go.

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Ah!

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There they go.

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In just a few seconds, the tapeworm cysts are in my stomach.

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That's full of acids that normally help protect us from disease.

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But the tapeworm uses our defences to its advantage.

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The acids dissolve the outer case of the cyst,

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releasing the worm inside.

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If they survive, each cyst will release a tapeworm scolex,

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equipped with four suckers, which it will use to latch onto my gut.

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Then it starts to grow, new segments emerging from the scolex.

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As it grows, the segments will get bigger and more mature,

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whilst new segments appear near the head.

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To see what a grown worm looks like,

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I met up with tapeworm expert, Prof Phil Craig.

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That is the adult tapeworm, and this tapeworm is exactly ten weeks old.

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We know that because it was from a previous volunteer.

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By ten weeks, the mature segments are full of eggs...

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..and they break off from the tapeworm and emerge from your body...

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..ready to infect a cow.

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So it comes out of your bottom, and it can actually crawl out?

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Unfortunately, yes.

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Psychologically, that upsets quite a few people that are infected.

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I can imagine.

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Yeah, it can come out under its own steam, as it were,

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so once the segment is in the rectum,

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it'll move around and that causes

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a sort of a strange fluttering sensation,

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and then it will move through the rectum, through the anus,

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and crawl around between the buttocks,

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down the legs and out onto the floor.

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-Right.

-Can be embarrassing.

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It might surprise my wife or friends.

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I think it probably would. Yes.

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After six weeks, I decided to take a look at my tapeworm,

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using a technique known as capsule endoscopy.

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Down the hatch.

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It involves a tiny camera which you swallow.

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Ah!

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Live from my stomach.

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Several hours later, the capsule had passed into my intestines,

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and using a tablet, I could see live pictures from my gut.

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Aah, that is it.

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That is the tapeworm.

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I can just see its tail and its segments waving around.

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I don't know if I'm absolutely disgusted or...

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I'm actually quite excited. Wow.

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Because it would have been hugely disappointing

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to have gone all the way to Kenya,

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come back and seen nothing.

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But what's amazing is, I've not experienced anything

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and yet you can see it there.

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That is so weird.

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This footage provides scientists with a rare chance

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to see a live worm in its natural habitat.

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So we sent the complete video to a team at Salford University.

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Just at the back there, you can just see the worm,

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the thinnest part of the worm.

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This is sort of the front end.

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The segments are getting more mature

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as you're moving down the intestine here,

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they're getting bigger, becoming sexually mature.

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Probably, they're starting to get fertilisation taking place,

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so the worm is actually starting to reproduce at this stage.

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Can you tell at this point how big it is? I have no idea of the scale.

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-By the looks of this, it's certainly over a metre in length.

-So a metre?

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That's another worm, yeah?

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-You have more than one worm, definitely.

-Right.

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I'll stop there. OK.

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-And guess what? You've got three worms.

-Oh, blimey.

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This is the very front end, the head end.

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This is the bit that attaches onto the intestine.

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There are actually four muscular suckers around that sort of head,

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and those are what's latching onto the wall of your intestine,

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-keeping the worm in place.

-Right. Wow.

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100% hit rate. I have to say, a very successful experiment.

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Humans are home to many parasites.

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The ones that live on our skin are called ectoparasites,

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and this is one of the most familiar ectoparasites -

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the head louse.

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To find out more about this very common parasite,

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I've come to a delousing salon in north London.

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What I'd love you to do, then, is infect me.

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Head lice can only survive by drinking human blood,

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which they do several times a day.

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To keep these lice alive, I need to feed them...on me.

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These little pots should keep them safe,

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while allowing them to bite me.

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-Thank you very much for infecting me.

-You're welcome.

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There aren't many people who would be pleased to hear

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their visitor is infested with lice.

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-Hi, James.

-Hello.

-I come bearing gifts.

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Oh, excellent.

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But James Logan is clearly delighted.

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Let's have a look. Oh, that's brilliant.

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James studies lice and other parasites

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at the London School of Hygiene and Tropical Medicine.

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-OK, so here we have one.

-Hm-hm.

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Shall we put it on your arm?

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Why not?

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See if he scurries around.

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Using a hand-held microscope,

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we can study my head louse as it settles in.

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You can really see the blood here, can't you?

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So this one's quite recently fed on your blood,

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but you can see it being sort of pumped down here through its gut.

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Like all lice, the head louse has retractable mouth parts

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that can puncture my skin.

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But what really surprised me is how active they can be.

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-It's going so fast, I can't keep up.

-This one's quite active, isn't it?

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It certainly is.

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Look at that, it's gone right to the last hair on your arm.

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Look at it clinging onto the edge of that hair with two of its claws.

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Look at those claws.

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It's got another claw out, and I wonder whether it's sat there

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waiting for another host to come past.

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So if I were to rub my head against yours,

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it would just grab a hold of your hair with the other claws

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-and it'd be across in an instant, would it?

-Exactly right, yeah.

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Although they feed on your skin,

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head lice always lay their eggs on hair,

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which is why they can only complete their life cycle on your head.

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But there is another species that lives on humans,

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and that can tell us something fascinating about our distant past.

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There's another type of louse called the body louse,

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and I've got an example here to show you what an infestation looks like.

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And this, remarkably, is highly adapted to clothing.

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This was actually... I believe, this was from a homeless person...

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-Yeah.

-...who had a very heavy infestation.

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And I think, it looks like trousers to me, with a seam here,

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and this is exactly where they lay their eggs.

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-Aah. That is revolting.

-You can see...

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Yeah, and those are eggs, so that is a massive infestation.

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-It makes you feel quite itchy, doesn't it?

-It does.

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The body louse behaves very differently to the head louse.

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But if you compare their bodies' shapes,

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you see something significant.

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OK, so the one on the right, the dark one,

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-is my friend, the head louse?

-Yep.

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He's looking dead at the moment, I have to say, not looking good.

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And the one on the left, they're body lice?

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That's exactly right.

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And what you can see is, they look remarkably similar.

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When you look at their DNA,

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what you find is that they diverged around 100 to 200,000 years ago,

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so not actually that long ago in sort of evolutionary terms,

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but enough to make them different species.

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And so that tells us something about when we, as humans,

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started to wear clothing.

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So before that, the idea is, humans were naked,

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then they started to wear clothes, maybe a head louse drops down,

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-thinks it's actually quite a nice place to live...

-Yep.

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..and begins to evolve, a whole new species starts to evolve on clothes.

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Exactly right, yep.

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So it's quite incredible to think you can look at the louse

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to find out more about our own ancestry and our own evolution.

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Some parasites cause relatively little harm to their host.

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But this one is deadly.

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It's a microscopic single-celled parasite...

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..called plasmodium.

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It causes malaria,

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a disease that kills more than half a million people a year.

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I want to find out why it is so deadly,

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so I've come to the National Institute of Medical Research,

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where they will infect my blood with plasmodium.

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So, I've got a sample of my blood here, looking nice and red. Healthy?

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Yes, yes, and warm, straight out of your body.

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-Hi there.

-Hi.

-I won't shake hands.

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-Thanks very much, Fiona.

-Right, I guess we're not allowed in that room.

-That's right, yeah.

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What's Fiona up to at the moment, then?

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So, what she's going to do now is

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she's going to take a sample of Plasmodium falciparum.

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So this is the most dangerous form of the parasite

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that causes most deaths in, for example, Sub-Saharan Africa.

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We've grown this in the lab,

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we can culture it continuously in human red cells,

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and she's now going to take a sample of those parasites

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-and inoculate them into your blood.

-Right.

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I must admit that of all the diseases,

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malaria is high on the ones I want to avoid.

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Well, you should try to avoid it if you can.

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To see the malaria parasite multiplying in my blood,

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they're using a new photographic time-lapse technique.

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Although I have treated people with malaria,

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I have never seen the malaria parasite in action before.

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Very intrigued to see what happens to my blood,

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but what is chilling is thinking that out there in the world,

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mosquitoes are infecting children.

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1,000 children every day are dying.

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That's why this sort of work is so important.

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Here it is. My blood infected by the deadly malaria parasite.

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So the parasite goes through this life cycle in the infected red cells.

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Once the infection is complete,

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Mike Blackman shows me the finished movie,

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which reveals how the parasite kills its host.

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So the little white blobs here, they are the parasite, right?

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They are the parasite, yeah.

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So a single merozoite, this invasive form of the parasite,

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binds to a red cell, invades it, grows within it,

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digests the haemoglobin of the red cell,

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this is the red protein that is used to carry oxygen via red cells,

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and then eventually forms around about 16 to 32 daughter merozoites.

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Does it? Oh, wow, look at that one go.

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-That one just exploded, didn't it?

-That's, right, exactly, yes.

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And suddenly you're seeing lots. Oh, wow, they're really going.

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The whole thing is destroyed in a single, very rapid process.

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The merozoites are released and they immediately invade a new cell,

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-and these things...

-I had no idea it was going to be that violent.

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I mean, that was utterly destroyed.

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Each explosion obliterates one of my oxygen-carrying red blood cells,

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and releases new parasites into my blood to infect yet more cells.

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Suddenly, you've gone from a situation where

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there are relatively few, they're everywhere,

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and they're just swarming.

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I mean, you do appreciate just what a terrible thing they're doing.

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Yeah, if this were going on inside you, you'd be in a pretty poor way.

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You soon become anaemic from lack of blood cells,

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and the debris from all those shattered cells can

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block your blood vessels, which in turn can be fatal.

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So our interest here is exactly how this goes on,

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how does the parasite actually do that? We don't really know.

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The parasite is very, very good, very smart.

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It's evolved with its human host for a long time.

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This is Toxoplasma gondii.

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It's a microscopic parasite that looks like a wriggling comma,

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and it's possibly the most prolific parasite that lives on humans.

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Its life cycle always passes through a cat,

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where the parasite breeds.

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An infected cat passes oocysts,

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tiny capsules containing the parasites.

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The oocysts can survive on the ground for months,

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waiting to be eaten by a rat or mouse,

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which then becomes a carrier.

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But for the life cycle to complete,

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the parasite has to get back into a cat,

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which means the mouse has to be caught and eaten by a cat.

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So, toxoplasma has to encourage its mouse host to commit suicide.

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A few years ago,

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Joanne Webster set up a series of elegant experiments to see

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how toxoplasma might go about altering a rodent's behaviour,

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making it more likely to get eaten.

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She placed infected and uninfected rats in a chamber

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where she had liberally doused one corner with cat urine.

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And we simply plopped the rat in and let them tootle about over

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each four-hour, ten-hour night, and simply watch where they went.

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Alice here is an uninfected female.

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She smelled the cat area and she shot off here.

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She seems to be avoiding the cat-smelling one.

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She's hanging around in different areas.

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Putting in a rat infected with toxoplasma

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produced a very different result.

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This is Felix here.

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He's infected and he's actually in the cat zone.

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Which is not what you'd expect. A normal mouse or rat would run...

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-Yeah, smell it and absolutely hide.

-And he seems to be just enjoying it.

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Yep, he's out, he's active, he's tootling about.

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So presumably, if you're the parasite, what you want is,

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you want the rat, Felix the Rat, to hang around

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-near where cats are because you want to be eaten.

-Yes.

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Joanne had shown that infected rats are attracted to cat smells.

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They're also generally more fearless

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and have slower reaction times.

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All these factors made them far more likely to become cat victims.

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What is rather disturbing is that this parasite, toxoplasma,

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also infects us.

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Around a quarter of the British population are infected

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without knowing it.

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You can catch it from cat litter.

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Or infected soil.

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Or from eating undercooked meat

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from an animal that was itself infected.

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Since toxoplasma can manipulate rat brains,

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can the parasite also change our behaviour?

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There's intriguing evidence that it can.

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Scientists have analysed blood samples from people

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involved in traffic accidents, and they found they are more than

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twice as likely to be infected with toxoplasma than the average.

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The claim is that infected people are slower to react

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and take greater risks -

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just like infected rats.

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Quite scary, isn't it,

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the thought of a parasite manipulating your behaviour?

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Absolutely, and I think the fact that it almost brings on

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the concept of free will,

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because how much of your behaviour you're expressing

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is yours and how much is it the parasite within you?

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Does toxoplasma change human behaviour?

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At the moment, there's no direct evidence.

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If there is an effect, it will be, in the vast majority of cases,

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very subtle.

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But the fact that it can alter a rat's behaviour

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is nothing short of remarkable.

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It shows just what extraordinary abilities evolution has

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equipped parasites with to ensure they spread to a new host.

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This is a leech.

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For thousands of years they were used to treat

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everything from skin diseases to fevers.

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Those cures almost certainly did more harm than good.

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But in the right hands, the leech can be a useful surgical assistant.

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Iain Whitaker is a reconstructive surgeon who is pioneering

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the modern use of leeches.

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I normally use them on extremities, for example a finger,

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or in rare instances, a nose or an ear.

0:20:060:20:08

-You're reattaching the end of a finger, something like that?

-Yes, that's right.

0:20:080:20:12

It is technically possible with microsurgery to attach the artery

0:20:120:20:15

so you've got blood flowing in,

0:20:150:20:17

but the blood flowing out via the veins is much more difficult.

0:20:170:20:20

-When things start to swell up?

-That's exactly right, that's the basis of it.

0:20:200:20:24

And the leeches are quite good at sort of controlling the flow,

0:20:240:20:27

-are they?

-Yeah, it's almost as if they're custom made.

0:20:270:20:30

You know, they remove a fairly predictable amount of blood,

0:20:300:20:33

it's self contained,

0:20:330:20:35

and they promote bleeding after they're removed as well.

0:20:350:20:38

It's the ability to remove blood that makes the leech

0:20:410:20:43

so useful in surgery.

0:20:430:20:46

But how much blood can a leech consume?

0:20:460:20:50

Well, there's one way to find out.

0:20:500:20:53

First, we have to see how much the hungry leech weighs.

0:20:530:20:57

-About point four.

-That's perfect.

-OK.

0:20:570:21:01

-So shall we put it on, are you ready?

-I'm ready, yeah.

0:21:010:21:04

They only need to feed once a year.

0:21:060:21:09

It takes about three months to digest a blood meal.

0:21:090:21:12

I can feel it, yeah.

0:21:130:21:15

I can definitely feel something going on there.

0:21:150:21:17

At the moment, it's attached by its head end,

0:21:170:21:21

where the jaws and teeth will have made a hole.

0:21:210:21:24

Here you can see how the leech's triple-jawed mouth is able to

0:21:250:21:30

cut through a membrane. That's what it's doing to my skin.

0:21:300:21:34

Once it's made a hole, it can start feeding on my blood.

0:21:380:21:41

It sucks by contracting its muscles

0:21:450:21:47

in a rhythmic movement called peristalsis.

0:21:470:21:51

Its digestive tract, visible here in red, can expand to

0:21:530:21:56

hold huge quantities of blood.

0:21:560:21:59

And its saliva contains proteins that help the blood keep flowing.

0:22:010:22:06

But it will be injecting some fairly ingenious things.

0:22:090:22:12

Hirudin is probably the most important,

0:22:120:22:15

which will prevent it clotting so it can feed more efficiently.

0:22:150:22:18

It's the most potent anti-coagulant known to man.

0:22:180:22:21

And how long will I go on bleeding for?

0:22:210:22:23

I think the average is about 12 hours.

0:22:230:22:26

In some instances, it can go up to 48, and 72 in extreme circumstances.

0:22:260:22:30

Oh, God, it's moved. It's come off.

0:22:300:22:33

-It fell off.

-Oh, there we go.

0:22:330:22:35

Shall we see how heavy it is?

0:22:350:22:37

-Hey, blimey, so it's now seven or eight times heavier.

-Yeah.

0:22:370:22:40

That is phenomenal, I mean, on you that would be...

0:22:400:22:43

The equivalent of me, 115 to 120 stone after one meal.

0:22:430:22:48

By helping blood to flow freely into newly re-attached tissues,

0:22:500:22:54

the leech can save parts of the body that would otherwise die.

0:22:540:22:58

Because it's a very upsetting injury to lose a finger or a thumb,

0:22:580:23:03

and leeches are literally the answer in some cases when we

0:23:030:23:06

can't get any other way to remove the blood, you know.

0:23:060:23:09

So they literally will save people's careers.

0:23:090:23:11

Parasites that live inside us, endoparasites, face a challenge.

0:23:190:23:24

They have to avoid attack from our immune system.

0:23:240:23:27

Helena Helmby studies how parasitic worms manage this feat.

0:23:290:23:33

The thing that puzzles me is,

0:23:330:23:35

how do these worms evade the human immune system?

0:23:350:23:38

Because, I mean, some of them are huge.

0:23:380:23:40

Yes, and we have a very, very sophisticated immune system,

0:23:400:23:44

which is constantly on watch

0:23:440:23:46

guarding against any microorganism 24/7.

0:23:460:23:49

But these large parasites have actually developed

0:23:490:23:54

a very sophisticated way of dealing with our immune system,

0:23:540:23:57

because they have evolved with us for thousands

0:23:570:23:59

if not millions of years.

0:23:590:24:02

The worms have evolved mechanisms to dampen down our immune responses,

0:24:020:24:07

by secreting compounds that manipulate our immune system.

0:24:070:24:12

That enables the worms to survive,

0:24:120:24:15

but may also have benefits for us.

0:24:150:24:18

The worms are allowed to stay because the immune system realises

0:24:180:24:22

that the attack to kill them

0:24:220:24:25

would be far too dangerous, really, for the host.

0:24:250:24:29

Obviously, you don't want a massive inflammatory response

0:24:290:24:32

in your intestine because that'd cause a lot of damage to your intestine

0:24:320:24:35

and that would be dangerous for you as a host,

0:24:350:24:37

so there's some sort of an uneasy truce

0:24:370:24:40

between the worm and the host in this case.

0:24:400:24:43

So our bodies have evolved a kind of ceasefire with the worms.

0:24:450:24:49

But in a modern, technological society,

0:24:490:24:53

most people spend their lives worm free.

0:24:530:24:56

Some scientists believe this may have contributed to

0:24:560:24:59

the rise of allergies.

0:24:590:25:02

It's known as the hygiene hypothesis.

0:25:030:25:06

This theory states that having parasites in your body

0:25:100:25:13

can help your immune system work properly.

0:25:130:25:17

It's not proven, but the evidence is intriguing.

0:25:170:25:20

There's no doubt that there has been a huge rise in allergies

0:25:210:25:24

and so-called autoimmune diseases

0:25:240:25:26

as we've got richer and more hygienic.

0:25:260:25:29

And rates of these diseases are highest in countries

0:25:310:25:34

that don't have lots of parasitic worms.

0:25:340:25:38

But what's controversial is that some people are now using worms

0:25:420:25:46

to try and treat their diseases.

0:25:460:25:49

Daniel Heyman has Crohn's.

0:25:510:25:53

I got ill...

0:25:530:25:55

'It's a debilitating condition in which the immune system in the gut

0:25:550:25:59

'starts attacking the body's own tissues.'

0:25:590:26:02

..when I'd lost several stone in weight

0:26:020:26:04

and I was bleeding internally, and so it was pretty serious.

0:26:040:26:09

And it took me a while to kind of work out

0:26:090:26:11

what I could eat and what I couldn't.

0:26:110:26:14

And curry was no longer...

0:26:140:26:15

Curry wasn't on the menu at all, no, no,

0:26:150:26:17

I was limited to sort of fish, rice, very plain foods.

0:26:170:26:20

'Although there are drugs that help,

0:26:230:26:25

'they can have unpleasant side effects.

0:26:250:26:28

'So Daniel decided to infect himself with hookworm,

0:26:280:26:31

'a small blood-sucking worm that lives in the intestines.

0:26:310:26:36

'Daniel hoped they would suppress his gut's immune system

0:26:380:26:41

'for their own survival and, by doing so, reduce his symptoms.

0:26:410:26:47

'Daniel ordered a tube of live hookworm on the internet,

0:26:470:26:51

'and placed them on his skin, where they burrowed in,

0:26:510:26:55

'eventually finding their way into his guts.

0:26:550:26:58

'That was two years ago.'

0:26:590:27:01

Do you have any fear of food at the moment?

0:27:010:27:03

No, I mean, I'm really free, like, thanks to the worms.

0:27:030:27:08

THEY LAUGH

0:27:080:27:10

I am basically free to eat as anyone else would.

0:27:100:27:13

'Daniel's story is fascinating,

0:27:140:27:17

'but to prove that hookworm treatment works,

0:27:170:27:20

'you need proper clinical trials.

0:27:200:27:22

'Without that evidence, Helena Helmby, like most scientists,

0:27:220:27:27

'finds the idea of self-infection very troubling.'

0:27:270:27:31

I mean, scientists have worked now for over 100 years

0:27:310:27:34

trying to eradicate these diseases, and now we want to start

0:27:340:27:37

reintroducing them into people again.

0:27:370:27:40

I mean, these worms actually live in the gut and they suck blood

0:27:400:27:45

from your intestinal mucosa.

0:27:450:27:47

And they move around a lot as they do that,

0:27:470:27:49

so they cause a lot of bleeding.

0:27:490:27:51

And if you have a high dose of hookworm in your gut,

0:27:510:27:53

you will become anaemic quite quickly.

0:27:530:27:56

Rather than infecting people with human parasites,

0:27:560:28:00

we should be really looking into

0:28:000:28:02

purifying these molecules that the worms produce,

0:28:020:28:05

and turn them into drugs.

0:28:050:28:07

Turn them into worm pills.

0:28:070:28:09

So parasites can teach us a great deal about our own bodies.

0:28:110:28:15

And they may even hold the key to future medical treatments.

0:28:170:28:20

Human parasites are a reminder that

0:28:210:28:25

we are just one part of a complex web of life

0:28:250:28:28

that has evolved with us,

0:28:280:28:31

making us who we are.

0:28:310:28:33

In this version of the BBC One series made especially for schools, Dr Michael Mosley explores the bizarre and fascinating world of parasites by turning his body into a living laboratory and deliberately infesting himself with them. He travels to Kenya to give himself tapeworm - a parasite that can grow to many metres inside the human gut - and then swallows a pill-camera to reveal what's growing inside him. He also encounters lice, leeches and the deadly malaria parasite - within him. By the end of his infestation, Michael learns a new-found respect for these extraordinary creatures, which can live off and even take control of their hosts for their own survival.