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The tapeworm. | 0:00:13 | 0:00:15 | |
It's one of nature's most fascinating parasites. | 0:00:15 | 0:00:19 | |
There are thousands of different kinds of tapeworm, | 0:00:21 | 0:00:24 | |
each evolved to live in a different host species. | 0:00:24 | 0:00:28 | |
And there are several species of tapeworm that live in humans, | 0:00:30 | 0:00:33 | |
including one called Taenia saginata. | 0:00:33 | 0:00:36 | |
Like many parasites, it has a complicated life cycle, | 0:00:38 | 0:00:41 | |
which involves passing through more than one species. | 0:00:41 | 0:00:45 | |
So imagine you're in rural Kenya | 0:00:47 | 0:00:48 | |
and you've got a great big tapeworm inside you. | 0:00:48 | 0:00:51 | |
This tapeworm is producing eggs. | 0:00:51 | 0:00:54 | |
One day, you go down to a field and you excrete there, | 0:00:54 | 0:00:58 | |
and you contaminate the grass. | 0:00:58 | 0:01:00 | |
Then along comes a poor unfortunate cow who eats that grass. | 0:01:00 | 0:01:05 | |
Along with grass, the cow eats the tapeworm eggs, | 0:01:08 | 0:01:11 | |
which hatch into larvae and then enter the cow's bloodstream... | 0:01:11 | 0:01:15 | |
..spreads through the blood to the muscle, | 0:01:17 | 0:01:19 | |
perhaps the shoulders or the tongue, | 0:01:19 | 0:01:21 | |
and there it forms a really tough cyst. | 0:01:21 | 0:01:24 | |
And it hangs around, just waiting for the next stage, | 0:01:24 | 0:01:28 | |
which is for the cow to be eaten by a human. | 0:01:28 | 0:01:31 | |
The beef tapeworm can only grow to adulthood inside a human, | 0:01:36 | 0:01:40 | |
and for that reason, it's hard to study. | 0:01:40 | 0:01:42 | |
So I've decided to infest myself, | 0:01:44 | 0:01:47 | |
as my contribution to research into these shy, retiring creatures. | 0:01:47 | 0:01:51 | |
So I need to find infected beef. | 0:01:53 | 0:01:56 | |
But in Britain, it's extremely unlikely | 0:01:59 | 0:02:01 | |
you'll find a contaminated cow, | 0:02:01 | 0:02:03 | |
which is why I've come to Kenya. | 0:02:03 | 0:02:05 | |
With the help of a local meat inspector, | 0:02:12 | 0:02:14 | |
we found some infected meat. | 0:02:14 | 0:02:16 | |
Then we cut three cysts out of the meat, | 0:02:19 | 0:02:22 | |
ready for me to swallow. | 0:02:22 | 0:02:24 | |
Cheers. | 0:02:26 | 0:02:28 | |
It's like jumping off a cliff. Here we go. | 0:02:30 | 0:02:32 | |
Ah! | 0:02:35 | 0:02:36 | |
There they go. | 0:02:38 | 0:02:40 | |
In just a few seconds, the tapeworm cysts are in my stomach. | 0:02:42 | 0:02:46 | |
That's full of acids that normally help protect us from disease. | 0:02:46 | 0:02:51 | |
But the tapeworm uses our defences to its advantage. | 0:02:54 | 0:02:58 | |
The acids dissolve the outer case of the cyst, | 0:02:58 | 0:03:02 | |
releasing the worm inside. | 0:03:02 | 0:03:03 | |
If they survive, each cyst will release a tapeworm scolex, | 0:03:10 | 0:03:15 | |
equipped with four suckers, which it will use to latch onto my gut. | 0:03:15 | 0:03:19 | |
Then it starts to grow, new segments emerging from the scolex. | 0:03:22 | 0:03:27 | |
As it grows, the segments will get bigger and more mature, | 0:03:31 | 0:03:36 | |
whilst new segments appear near the head. | 0:03:36 | 0:03:39 | |
To see what a grown worm looks like, | 0:03:41 | 0:03:43 | |
I met up with tapeworm expert, Prof Phil Craig. | 0:03:43 | 0:03:48 | |
That is the adult tapeworm, and this tapeworm is exactly ten weeks old. | 0:03:50 | 0:03:55 | |
We know that because it was from a previous volunteer. | 0:03:55 | 0:03:58 | |
By ten weeks, the mature segments are full of eggs... | 0:04:01 | 0:04:05 | |
..and they break off from the tapeworm and emerge from your body... | 0:04:06 | 0:04:10 | |
..ready to infect a cow. | 0:04:12 | 0:04:14 | |
So it comes out of your bottom, and it can actually crawl out? | 0:04:17 | 0:04:22 | |
Unfortunately, yes. | 0:04:22 | 0:04:24 | |
Psychologically, that upsets quite a few people that are infected. | 0:04:24 | 0:04:27 | |
I can imagine. | 0:04:27 | 0:04:29 | |
Yeah, it can come out under its own steam, as it were, | 0:04:29 | 0:04:31 | |
so once the segment is in the rectum, | 0:04:31 | 0:04:34 | |
it'll move around and that causes | 0:04:34 | 0:04:35 | |
a sort of a strange fluttering sensation, | 0:04:35 | 0:04:39 | |
and then it will move through the rectum, through the anus, | 0:04:39 | 0:04:43 | |
and crawl around between the buttocks, | 0:04:43 | 0:04:45 | |
down the legs and out onto the floor. | 0:04:45 | 0:04:49 | |
-Right. -Can be embarrassing. | 0:04:49 | 0:04:50 | |
It might surprise my wife or friends. | 0:04:50 | 0:04:52 | |
I think it probably would. Yes. | 0:04:52 | 0:04:54 | |
After six weeks, I decided to take a look at my tapeworm, | 0:04:56 | 0:05:00 | |
using a technique known as capsule endoscopy. | 0:05:00 | 0:05:03 | |
Down the hatch. | 0:05:05 | 0:05:06 | |
It involves a tiny camera which you swallow. | 0:05:06 | 0:05:08 | |
Ah! | 0:05:08 | 0:05:11 | |
Live from my stomach. | 0:05:11 | 0:05:12 | |
Several hours later, the capsule had passed into my intestines, | 0:05:13 | 0:05:17 | |
and using a tablet, I could see live pictures from my gut. | 0:05:17 | 0:05:21 | |
Aah, that is it. | 0:05:21 | 0:05:25 | |
That is the tapeworm. | 0:05:25 | 0:05:27 | |
I can just see its tail and its segments waving around. | 0:05:27 | 0:05:31 | |
I don't know if I'm absolutely disgusted or... | 0:05:31 | 0:05:34 | |
I'm actually quite excited. Wow. | 0:05:34 | 0:05:36 | |
Because it would have been hugely disappointing | 0:05:37 | 0:05:39 | |
to have gone all the way to Kenya, | 0:05:39 | 0:05:41 | |
come back and seen nothing. | 0:05:41 | 0:05:42 | |
But what's amazing is, I've not experienced anything | 0:05:42 | 0:05:45 | |
and yet you can see it there. | 0:05:45 | 0:05:47 | |
That is so weird. | 0:05:47 | 0:05:51 | |
This footage provides scientists with a rare chance | 0:05:51 | 0:05:54 | |
to see a live worm in its natural habitat. | 0:05:54 | 0:05:58 | |
So we sent the complete video to a team at Salford University. | 0:05:58 | 0:06:02 | |
Just at the back there, you can just see the worm, | 0:06:02 | 0:06:05 | |
the thinnest part of the worm. | 0:06:05 | 0:06:07 | |
This is sort of the front end. | 0:06:07 | 0:06:08 | |
The segments are getting more mature | 0:06:08 | 0:06:10 | |
as you're moving down the intestine here, | 0:06:10 | 0:06:12 | |
they're getting bigger, becoming sexually mature. | 0:06:12 | 0:06:15 | |
Probably, they're starting to get fertilisation taking place, | 0:06:15 | 0:06:20 | |
so the worm is actually starting to reproduce at this stage. | 0:06:20 | 0:06:23 | |
Can you tell at this point how big it is? I have no idea of the scale. | 0:06:23 | 0:06:27 | |
-By the looks of this, it's certainly over a metre in length. -So a metre? | 0:06:27 | 0:06:32 | |
That's another worm, yeah? | 0:06:37 | 0:06:41 | |
-You have more than one worm, definitely. -Right. | 0:06:41 | 0:06:45 | |
I'll stop there. OK. | 0:06:46 | 0:06:47 | |
-And guess what? You've got three worms. -Oh, blimey. | 0:06:47 | 0:06:51 | |
This is the very front end, the head end. | 0:06:51 | 0:06:54 | |
This is the bit that attaches onto the intestine. | 0:06:54 | 0:06:56 | |
There are actually four muscular suckers around that sort of head, | 0:06:56 | 0:07:00 | |
and those are what's latching onto the wall of your intestine, | 0:07:00 | 0:07:04 | |
-keeping the worm in place. -Right. Wow. | 0:07:04 | 0:07:06 | |
100% hit rate. I have to say, a very successful experiment. | 0:07:06 | 0:07:11 | |
Humans are home to many parasites. | 0:07:14 | 0:07:16 | |
The ones that live on our skin are called ectoparasites, | 0:07:16 | 0:07:20 | |
and this is one of the most familiar ectoparasites - | 0:07:20 | 0:07:25 | |
the head louse. | 0:07:25 | 0:07:27 | |
To find out more about this very common parasite, | 0:07:30 | 0:07:33 | |
I've come to a delousing salon in north London. | 0:07:33 | 0:07:37 | |
What I'd love you to do, then, is infect me. | 0:07:41 | 0:07:44 | |
Head lice can only survive by drinking human blood, | 0:07:45 | 0:07:48 | |
which they do several times a day. | 0:07:48 | 0:07:51 | |
To keep these lice alive, I need to feed them...on me. | 0:07:52 | 0:07:56 | |
These little pots should keep them safe, | 0:07:59 | 0:08:01 | |
while allowing them to bite me. | 0:08:01 | 0:08:03 | |
-Thank you very much for infecting me. -You're welcome. | 0:08:04 | 0:08:07 | |
There aren't many people who would be pleased to hear | 0:08:09 | 0:08:11 | |
their visitor is infested with lice. | 0:08:11 | 0:08:13 | |
-Hi, James. -Hello. -I come bearing gifts. | 0:08:13 | 0:08:17 | |
Oh, excellent. | 0:08:17 | 0:08:18 | |
But James Logan is clearly delighted. | 0:08:18 | 0:08:21 | |
Let's have a look. Oh, that's brilliant. | 0:08:21 | 0:08:23 | |
James studies lice and other parasites | 0:08:23 | 0:08:25 | |
at the London School of Hygiene and Tropical Medicine. | 0:08:25 | 0:08:28 | |
-OK, so here we have one. -Hm-hm. | 0:08:28 | 0:08:31 | |
Shall we put it on your arm? | 0:08:31 | 0:08:33 | |
Why not? | 0:08:33 | 0:08:34 | |
See if he scurries around. | 0:08:34 | 0:08:37 | |
Using a hand-held microscope, | 0:08:37 | 0:08:39 | |
we can study my head louse as it settles in. | 0:08:39 | 0:08:41 | |
You can really see the blood here, can't you? | 0:08:43 | 0:08:46 | |
So this one's quite recently fed on your blood, | 0:08:46 | 0:08:48 | |
but you can see it being sort of pumped down here through its gut. | 0:08:48 | 0:08:52 | |
Like all lice, the head louse has retractable mouth parts | 0:08:53 | 0:08:57 | |
that can puncture my skin. | 0:08:57 | 0:08:59 | |
But what really surprised me is how active they can be. | 0:09:01 | 0:09:04 | |
-It's going so fast, I can't keep up. -This one's quite active, isn't it? | 0:09:05 | 0:09:08 | |
It certainly is. | 0:09:08 | 0:09:10 | |
Look at that, it's gone right to the last hair on your arm. | 0:09:10 | 0:09:13 | |
Look at it clinging onto the edge of that hair with two of its claws. | 0:09:13 | 0:09:17 | |
Look at those claws. | 0:09:17 | 0:09:18 | |
It's got another claw out, and I wonder whether it's sat there | 0:09:18 | 0:09:20 | |
waiting for another host to come past. | 0:09:20 | 0:09:22 | |
So if I were to rub my head against yours, | 0:09:22 | 0:09:25 | |
it would just grab a hold of your hair with the other claws | 0:09:25 | 0:09:29 | |
-and it'd be across in an instant, would it? -Exactly right, yeah. | 0:09:29 | 0:09:33 | |
Although they feed on your skin, | 0:09:33 | 0:09:35 | |
head lice always lay their eggs on hair, | 0:09:35 | 0:09:39 | |
which is why they can only complete their life cycle on your head. | 0:09:39 | 0:09:43 | |
But there is another species that lives on humans, | 0:09:44 | 0:09:48 | |
and that can tell us something fascinating about our distant past. | 0:09:48 | 0:09:52 | |
There's another type of louse called the body louse, | 0:09:53 | 0:09:55 | |
and I've got an example here to show you what an infestation looks like. | 0:09:55 | 0:09:59 | |
And this, remarkably, is highly adapted to clothing. | 0:09:59 | 0:10:03 | |
This was actually... I believe, this was from a homeless person... | 0:10:03 | 0:10:07 | |
-Yeah. -...who had a very heavy infestation. | 0:10:07 | 0:10:09 | |
And I think, it looks like trousers to me, with a seam here, | 0:10:09 | 0:10:12 | |
and this is exactly where they lay their eggs. | 0:10:12 | 0:10:15 | |
-Aah. That is revolting. -You can see... | 0:10:15 | 0:10:17 | |
Yeah, and those are eggs, so that is a massive infestation. | 0:10:17 | 0:10:21 | |
-It makes you feel quite itchy, doesn't it? -It does. | 0:10:21 | 0:10:23 | |
The body louse behaves very differently to the head louse. | 0:10:25 | 0:10:28 | |
But if you compare their bodies' shapes, | 0:10:28 | 0:10:31 | |
you see something significant. | 0:10:31 | 0:10:34 | |
OK, so the one on the right, the dark one, | 0:10:34 | 0:10:36 | |
-is my friend, the head louse? -Yep. | 0:10:36 | 0:10:37 | |
He's looking dead at the moment, I have to say, not looking good. | 0:10:37 | 0:10:40 | |
And the one on the left, they're body lice? | 0:10:40 | 0:10:42 | |
That's exactly right. | 0:10:42 | 0:10:44 | |
And what you can see is, they look remarkably similar. | 0:10:44 | 0:10:46 | |
When you look at their DNA, | 0:10:46 | 0:10:47 | |
what you find is that they diverged around 100 to 200,000 years ago, | 0:10:47 | 0:10:50 | |
so not actually that long ago in sort of evolutionary terms, | 0:10:50 | 0:10:53 | |
but enough to make them different species. | 0:10:53 | 0:10:56 | |
And so that tells us something about when we, as humans, | 0:10:56 | 0:10:58 | |
started to wear clothing. | 0:10:58 | 0:11:00 | |
So before that, the idea is, humans were naked, | 0:11:00 | 0:11:02 | |
then they started to wear clothes, maybe a head louse drops down, | 0:11:02 | 0:11:06 | |
-thinks it's actually quite a nice place to live... -Yep. | 0:11:06 | 0:11:08 | |
..and begins to evolve, a whole new species starts to evolve on clothes. | 0:11:08 | 0:11:11 | |
Exactly right, yep. | 0:11:11 | 0:11:13 | |
So it's quite incredible to think you can look at the louse | 0:11:13 | 0:11:15 | |
to find out more about our own ancestry and our own evolution. | 0:11:15 | 0:11:19 | |
Some parasites cause relatively little harm to their host. | 0:11:22 | 0:11:27 | |
But this one is deadly. | 0:11:27 | 0:11:29 | |
It's a microscopic single-celled parasite... | 0:11:30 | 0:11:34 | |
..called plasmodium. | 0:11:35 | 0:11:37 | |
It causes malaria, | 0:11:39 | 0:11:41 | |
a disease that kills more than half a million people a year. | 0:11:41 | 0:11:45 | |
I want to find out why it is so deadly, | 0:11:49 | 0:11:53 | |
so I've come to the National Institute of Medical Research, | 0:11:53 | 0:11:56 | |
where they will infect my blood with plasmodium. | 0:11:56 | 0:11:59 | |
So, I've got a sample of my blood here, looking nice and red. Healthy? | 0:12:03 | 0:12:06 | |
Yes, yes, and warm, straight out of your body. | 0:12:06 | 0:12:09 | |
-Hi there. -Hi. -I won't shake hands. | 0:12:10 | 0:12:12 | |
-Thanks very much, Fiona. -Right, I guess we're not allowed in that room. -That's right, yeah. | 0:12:13 | 0:12:18 | |
What's Fiona up to at the moment, then? | 0:12:18 | 0:12:20 | |
So, what she's going to do now is | 0:12:20 | 0:12:22 | |
she's going to take a sample of Plasmodium falciparum. | 0:12:22 | 0:12:25 | |
So this is the most dangerous form of the parasite | 0:12:25 | 0:12:28 | |
that causes most deaths in, for example, Sub-Saharan Africa. | 0:12:28 | 0:12:31 | |
We've grown this in the lab, | 0:12:31 | 0:12:33 | |
we can culture it continuously in human red cells, | 0:12:33 | 0:12:35 | |
and she's now going to take a sample of those parasites | 0:12:35 | 0:12:37 | |
-and inoculate them into your blood. -Right. | 0:12:37 | 0:12:39 | |
I must admit that of all the diseases, | 0:12:39 | 0:12:41 | |
malaria is high on the ones I want to avoid. | 0:12:41 | 0:12:44 | |
Well, you should try to avoid it if you can. | 0:12:44 | 0:12:46 | |
To see the malaria parasite multiplying in my blood, | 0:12:48 | 0:12:52 | |
they're using a new photographic time-lapse technique. | 0:12:52 | 0:12:55 | |
Although I have treated people with malaria, | 0:12:55 | 0:12:57 | |
I have never seen the malaria parasite in action before. | 0:12:57 | 0:13:01 | |
Very intrigued to see what happens to my blood, | 0:13:02 | 0:13:04 | |
but what is chilling is thinking that out there in the world, | 0:13:04 | 0:13:09 | |
mosquitoes are infecting children. | 0:13:09 | 0:13:11 | |
1,000 children every day are dying. | 0:13:11 | 0:13:13 | |
That's why this sort of work is so important. | 0:13:13 | 0:13:16 | |
Here it is. My blood infected by the deadly malaria parasite. | 0:13:18 | 0:13:22 | |
So the parasite goes through this life cycle in the infected red cells. | 0:13:23 | 0:13:28 | |
Once the infection is complete, | 0:13:28 | 0:13:30 | |
Mike Blackman shows me the finished movie, | 0:13:30 | 0:13:33 | |
which reveals how the parasite kills its host. | 0:13:33 | 0:13:36 | |
So the little white blobs here, they are the parasite, right? | 0:13:36 | 0:13:39 | |
They are the parasite, yeah. | 0:13:39 | 0:13:41 | |
So a single merozoite, this invasive form of the parasite, | 0:13:41 | 0:13:45 | |
binds to a red cell, invades it, grows within it, | 0:13:45 | 0:13:49 | |
digests the haemoglobin of the red cell, | 0:13:49 | 0:13:51 | |
this is the red protein that is used to carry oxygen via red cells, | 0:13:51 | 0:13:55 | |
and then eventually forms around about 16 to 32 daughter merozoites. | 0:13:55 | 0:14:01 | |
Does it? Oh, wow, look at that one go. | 0:14:01 | 0:14:04 | |
-That one just exploded, didn't it? -That's, right, exactly, yes. | 0:14:04 | 0:14:06 | |
And suddenly you're seeing lots. Oh, wow, they're really going. | 0:14:06 | 0:14:10 | |
The whole thing is destroyed in a single, very rapid process. | 0:14:12 | 0:14:16 | |
The merozoites are released and they immediately invade a new cell, | 0:14:16 | 0:14:20 | |
-and these things... -I had no idea it was going to be that violent. | 0:14:20 | 0:14:23 | |
I mean, that was utterly destroyed. | 0:14:23 | 0:14:25 | |
Each explosion obliterates one of my oxygen-carrying red blood cells, | 0:14:25 | 0:14:30 | |
and releases new parasites into my blood to infect yet more cells. | 0:14:30 | 0:14:35 | |
Suddenly, you've gone from a situation where | 0:14:37 | 0:14:39 | |
there are relatively few, they're everywhere, | 0:14:39 | 0:14:41 | |
and they're just swarming. | 0:14:41 | 0:14:43 | |
I mean, you do appreciate just what a terrible thing they're doing. | 0:14:43 | 0:14:46 | |
Yeah, if this were going on inside you, you'd be in a pretty poor way. | 0:14:46 | 0:14:51 | |
You soon become anaemic from lack of blood cells, | 0:14:51 | 0:14:54 | |
and the debris from all those shattered cells can | 0:14:54 | 0:14:57 | |
block your blood vessels, which in turn can be fatal. | 0:14:57 | 0:15:00 | |
So our interest here is exactly how this goes on, | 0:15:02 | 0:15:05 | |
how does the parasite actually do that? We don't really know. | 0:15:05 | 0:15:08 | |
The parasite is very, very good, very smart. | 0:15:08 | 0:15:10 | |
It's evolved with its human host for a long time. | 0:15:10 | 0:15:14 | |
This is Toxoplasma gondii. | 0:15:16 | 0:15:18 | |
It's a microscopic parasite that looks like a wriggling comma, | 0:15:20 | 0:15:24 | |
and it's possibly the most prolific parasite that lives on humans. | 0:15:24 | 0:15:29 | |
Its life cycle always passes through a cat, | 0:15:31 | 0:15:34 | |
where the parasite breeds. | 0:15:34 | 0:15:35 | |
An infected cat passes oocysts, | 0:15:38 | 0:15:42 | |
tiny capsules containing the parasites. | 0:15:42 | 0:15:46 | |
The oocysts can survive on the ground for months, | 0:15:46 | 0:15:49 | |
waiting to be eaten by a rat or mouse, | 0:15:49 | 0:15:53 | |
which then becomes a carrier. | 0:15:53 | 0:15:55 | |
But for the life cycle to complete, | 0:15:58 | 0:16:00 | |
the parasite has to get back into a cat, | 0:16:00 | 0:16:03 | |
which means the mouse has to be caught and eaten by a cat. | 0:16:03 | 0:16:08 | |
So, toxoplasma has to encourage its mouse host to commit suicide. | 0:16:11 | 0:16:17 | |
A few years ago, | 0:16:20 | 0:16:21 | |
Joanne Webster set up a series of elegant experiments to see | 0:16:21 | 0:16:24 | |
how toxoplasma might go about altering a rodent's behaviour, | 0:16:24 | 0:16:30 | |
making it more likely to get eaten. | 0:16:30 | 0:16:32 | |
She placed infected and uninfected rats in a chamber | 0:16:34 | 0:16:37 | |
where she had liberally doused one corner with cat urine. | 0:16:37 | 0:16:41 | |
And we simply plopped the rat in and let them tootle about over | 0:16:41 | 0:16:45 | |
each four-hour, ten-hour night, and simply watch where they went. | 0:16:45 | 0:16:49 | |
Alice here is an uninfected female. | 0:16:49 | 0:16:51 | |
She smelled the cat area and she shot off here. | 0:16:51 | 0:16:54 | |
She seems to be avoiding the cat-smelling one. | 0:16:54 | 0:16:57 | |
She's hanging around in different areas. | 0:16:57 | 0:17:00 | |
Putting in a rat infected with toxoplasma | 0:17:00 | 0:17:03 | |
produced a very different result. | 0:17:03 | 0:17:05 | |
This is Felix here. | 0:17:05 | 0:17:07 | |
He's infected and he's actually in the cat zone. | 0:17:07 | 0:17:09 | |
Which is not what you'd expect. A normal mouse or rat would run... | 0:17:09 | 0:17:12 | |
-Yeah, smell it and absolutely hide. -And he seems to be just enjoying it. | 0:17:12 | 0:17:16 | |
Yep, he's out, he's active, he's tootling about. | 0:17:16 | 0:17:19 | |
So presumably, if you're the parasite, what you want is, | 0:17:19 | 0:17:22 | |
you want the rat, Felix the Rat, to hang around | 0:17:22 | 0:17:26 | |
-near where cats are because you want to be eaten. -Yes. | 0:17:26 | 0:17:29 | |
Joanne had shown that infected rats are attracted to cat smells. | 0:17:30 | 0:17:35 | |
They're also generally more fearless | 0:17:35 | 0:17:37 | |
and have slower reaction times. | 0:17:37 | 0:17:40 | |
All these factors made them far more likely to become cat victims. | 0:17:40 | 0:17:45 | |
What is rather disturbing is that this parasite, toxoplasma, | 0:17:45 | 0:17:50 | |
also infects us. | 0:17:50 | 0:17:53 | |
Around a quarter of the British population are infected | 0:17:53 | 0:17:55 | |
without knowing it. | 0:17:55 | 0:17:57 | |
You can catch it from cat litter. | 0:17:57 | 0:17:59 | |
Or infected soil. | 0:18:01 | 0:18:02 | |
Or from eating undercooked meat | 0:18:04 | 0:18:07 | |
from an animal that was itself infected. | 0:18:07 | 0:18:09 | |
Since toxoplasma can manipulate rat brains, | 0:18:13 | 0:18:16 | |
can the parasite also change our behaviour? | 0:18:16 | 0:18:21 | |
There's intriguing evidence that it can. | 0:18:21 | 0:18:23 | |
Scientists have analysed blood samples from people | 0:18:26 | 0:18:29 | |
involved in traffic accidents, and they found they are more than | 0:18:29 | 0:18:32 | |
twice as likely to be infected with toxoplasma than the average. | 0:18:32 | 0:18:37 | |
The claim is that infected people are slower to react | 0:18:38 | 0:18:41 | |
and take greater risks - | 0:18:41 | 0:18:43 | |
just like infected rats. | 0:18:43 | 0:18:45 | |
Quite scary, isn't it, | 0:18:48 | 0:18:50 | |
the thought of a parasite manipulating your behaviour? | 0:18:50 | 0:18:52 | |
Absolutely, and I think the fact that it almost brings on | 0:18:52 | 0:18:55 | |
the concept of free will, | 0:18:55 | 0:18:56 | |
because how much of your behaviour you're expressing | 0:18:56 | 0:18:59 | |
is yours and how much is it the parasite within you? | 0:18:59 | 0:19:02 | |
Does toxoplasma change human behaviour? | 0:19:02 | 0:19:06 | |
At the moment, there's no direct evidence. | 0:19:06 | 0:19:10 | |
If there is an effect, it will be, in the vast majority of cases, | 0:19:10 | 0:19:14 | |
very subtle. | 0:19:14 | 0:19:15 | |
But the fact that it can alter a rat's behaviour | 0:19:15 | 0:19:19 | |
is nothing short of remarkable. | 0:19:19 | 0:19:22 | |
It shows just what extraordinary abilities evolution has | 0:19:22 | 0:19:25 | |
equipped parasites with to ensure they spread to a new host. | 0:19:25 | 0:19:30 | |
This is a leech. | 0:19:36 | 0:19:39 | |
For thousands of years they were used to treat | 0:19:39 | 0:19:41 | |
everything from skin diseases to fevers. | 0:19:41 | 0:19:44 | |
Those cures almost certainly did more harm than good. | 0:19:44 | 0:19:47 | |
But in the right hands, the leech can be a useful surgical assistant. | 0:19:49 | 0:19:53 | |
Iain Whitaker is a reconstructive surgeon who is pioneering | 0:19:56 | 0:19:59 | |
the modern use of leeches. | 0:19:59 | 0:20:01 | |
I normally use them on extremities, for example a finger, | 0:20:02 | 0:20:06 | |
or in rare instances, a nose or an ear. | 0:20:06 | 0:20:08 | |
-You're reattaching the end of a finger, something like that? -Yes, that's right. | 0:20:08 | 0:20:12 | |
It is technically possible with microsurgery to attach the artery | 0:20:12 | 0:20:15 | |
so you've got blood flowing in, | 0:20:15 | 0:20:17 | |
but the blood flowing out via the veins is much more difficult. | 0:20:17 | 0:20:20 | |
-When things start to swell up? -That's exactly right, that's the basis of it. | 0:20:20 | 0:20:24 | |
And the leeches are quite good at sort of controlling the flow, | 0:20:24 | 0:20:27 | |
-are they? -Yeah, it's almost as if they're custom made. | 0:20:27 | 0:20:30 | |
You know, they remove a fairly predictable amount of blood, | 0:20:30 | 0:20:33 | |
it's self contained, | 0:20:33 | 0:20:35 | |
and they promote bleeding after they're removed as well. | 0:20:35 | 0:20:38 | |
It's the ability to remove blood that makes the leech | 0:20:41 | 0:20:43 | |
so useful in surgery. | 0:20:43 | 0:20:46 | |
But how much blood can a leech consume? | 0:20:46 | 0:20:50 | |
Well, there's one way to find out. | 0:20:50 | 0:20:53 | |
First, we have to see how much the hungry leech weighs. | 0:20:53 | 0:20:57 | |
-About point four. -That's perfect. -OK. | 0:20:57 | 0:21:01 | |
-So shall we put it on, are you ready? -I'm ready, yeah. | 0:21:01 | 0:21:04 | |
They only need to feed once a year. | 0:21:06 | 0:21:09 | |
It takes about three months to digest a blood meal. | 0:21:09 | 0:21:12 | |
I can feel it, yeah. | 0:21:13 | 0:21:15 | |
I can definitely feel something going on there. | 0:21:15 | 0:21:17 | |
At the moment, it's attached by its head end, | 0:21:17 | 0:21:21 | |
where the jaws and teeth will have made a hole. | 0:21:21 | 0:21:24 | |
Here you can see how the leech's triple-jawed mouth is able to | 0:21:25 | 0:21:30 | |
cut through a membrane. That's what it's doing to my skin. | 0:21:30 | 0:21:34 | |
Once it's made a hole, it can start feeding on my blood. | 0:21:38 | 0:21:41 | |
It sucks by contracting its muscles | 0:21:45 | 0:21:47 | |
in a rhythmic movement called peristalsis. | 0:21:47 | 0:21:51 | |
Its digestive tract, visible here in red, can expand to | 0:21:53 | 0:21:56 | |
hold huge quantities of blood. | 0:21:56 | 0:21:59 | |
And its saliva contains proteins that help the blood keep flowing. | 0:22:01 | 0:22:06 | |
But it will be injecting some fairly ingenious things. | 0:22:09 | 0:22:12 | |
Hirudin is probably the most important, | 0:22:12 | 0:22:15 | |
which will prevent it clotting so it can feed more efficiently. | 0:22:15 | 0:22:18 | |
It's the most potent anti-coagulant known to man. | 0:22:18 | 0:22:21 | |
And how long will I go on bleeding for? | 0:22:21 | 0:22:23 | |
I think the average is about 12 hours. | 0:22:23 | 0:22:26 | |
In some instances, it can go up to 48, and 72 in extreme circumstances. | 0:22:26 | 0:22:30 | |
Oh, God, it's moved. It's come off. | 0:22:30 | 0:22:33 | |
-It fell off. -Oh, there we go. | 0:22:33 | 0:22:35 | |
Shall we see how heavy it is? | 0:22:35 | 0:22:37 | |
-Hey, blimey, so it's now seven or eight times heavier. -Yeah. | 0:22:37 | 0:22:40 | |
That is phenomenal, I mean, on you that would be... | 0:22:40 | 0:22:43 | |
The equivalent of me, 115 to 120 stone after one meal. | 0:22:43 | 0:22:48 | |
By helping blood to flow freely into newly re-attached tissues, | 0:22:50 | 0:22:54 | |
the leech can save parts of the body that would otherwise die. | 0:22:54 | 0:22:58 | |
Because it's a very upsetting injury to lose a finger or a thumb, | 0:22:58 | 0:23:03 | |
and leeches are literally the answer in some cases when we | 0:23:03 | 0:23:06 | |
can't get any other way to remove the blood, you know. | 0:23:06 | 0:23:09 | |
So they literally will save people's careers. | 0:23:09 | 0:23:11 | |
Parasites that live inside us, endoparasites, face a challenge. | 0:23:19 | 0:23:24 | |
They have to avoid attack from our immune system. | 0:23:24 | 0:23:27 | |
Helena Helmby studies how parasitic worms manage this feat. | 0:23:29 | 0:23:33 | |
The thing that puzzles me is, | 0:23:33 | 0:23:35 | |
how do these worms evade the human immune system? | 0:23:35 | 0:23:38 | |
Because, I mean, some of them are huge. | 0:23:38 | 0:23:40 | |
Yes, and we have a very, very sophisticated immune system, | 0:23:40 | 0:23:44 | |
which is constantly on watch | 0:23:44 | 0:23:46 | |
guarding against any microorganism 24/7. | 0:23:46 | 0:23:49 | |
But these large parasites have actually developed | 0:23:49 | 0:23:54 | |
a very sophisticated way of dealing with our immune system, | 0:23:54 | 0:23:57 | |
because they have evolved with us for thousands | 0:23:57 | 0:23:59 | |
if not millions of years. | 0:23:59 | 0:24:02 | |
The worms have evolved mechanisms to dampen down our immune responses, | 0:24:02 | 0:24:07 | |
by secreting compounds that manipulate our immune system. | 0:24:07 | 0:24:12 | |
That enables the worms to survive, | 0:24:12 | 0:24:15 | |
but may also have benefits for us. | 0:24:15 | 0:24:18 | |
The worms are allowed to stay because the immune system realises | 0:24:18 | 0:24:22 | |
that the attack to kill them | 0:24:22 | 0:24:25 | |
would be far too dangerous, really, for the host. | 0:24:25 | 0:24:29 | |
Obviously, you don't want a massive inflammatory response | 0:24:29 | 0:24:32 | |
in your intestine because that'd cause a lot of damage to your intestine | 0:24:32 | 0:24:35 | |
and that would be dangerous for you as a host, | 0:24:35 | 0:24:37 | |
so there's some sort of an uneasy truce | 0:24:37 | 0:24:40 | |
between the worm and the host in this case. | 0:24:40 | 0:24:43 | |
So our bodies have evolved a kind of ceasefire with the worms. | 0:24:45 | 0:24:49 | |
But in a modern, technological society, | 0:24:49 | 0:24:53 | |
most people spend their lives worm free. | 0:24:53 | 0:24:56 | |
Some scientists believe this may have contributed to | 0:24:56 | 0:24:59 | |
the rise of allergies. | 0:24:59 | 0:25:02 | |
It's known as the hygiene hypothesis. | 0:25:03 | 0:25:06 | |
This theory states that having parasites in your body | 0:25:10 | 0:25:13 | |
can help your immune system work properly. | 0:25:13 | 0:25:17 | |
It's not proven, but the evidence is intriguing. | 0:25:17 | 0:25:20 | |
There's no doubt that there has been a huge rise in allergies | 0:25:21 | 0:25:24 | |
and so-called autoimmune diseases | 0:25:24 | 0:25:26 | |
as we've got richer and more hygienic. | 0:25:26 | 0:25:29 | |
And rates of these diseases are highest in countries | 0:25:31 | 0:25:34 | |
that don't have lots of parasitic worms. | 0:25:34 | 0:25:38 | |
But what's controversial is that some people are now using worms | 0:25:42 | 0:25:46 | |
to try and treat their diseases. | 0:25:46 | 0:25:49 | |
Daniel Heyman has Crohn's. | 0:25:51 | 0:25:53 | |
I got ill... | 0:25:53 | 0:25:55 | |
'It's a debilitating condition in which the immune system in the gut | 0:25:55 | 0:25:59 | |
'starts attacking the body's own tissues.' | 0:25:59 | 0:26:02 | |
..when I'd lost several stone in weight | 0:26:02 | 0:26:04 | |
and I was bleeding internally, and so it was pretty serious. | 0:26:04 | 0:26:09 | |
And it took me a while to kind of work out | 0:26:09 | 0:26:11 | |
what I could eat and what I couldn't. | 0:26:11 | 0:26:14 | |
And curry was no longer... | 0:26:14 | 0:26:15 | |
Curry wasn't on the menu at all, no, no, | 0:26:15 | 0:26:17 | |
I was limited to sort of fish, rice, very plain foods. | 0:26:17 | 0:26:20 | |
'Although there are drugs that help, | 0:26:23 | 0:26:25 | |
'they can have unpleasant side effects. | 0:26:25 | 0:26:28 | |
'So Daniel decided to infect himself with hookworm, | 0:26:28 | 0:26:31 | |
'a small blood-sucking worm that lives in the intestines. | 0:26:31 | 0:26:36 | |
'Daniel hoped they would suppress his gut's immune system | 0:26:38 | 0:26:41 | |
'for their own survival and, by doing so, reduce his symptoms. | 0:26:41 | 0:26:47 | |
'Daniel ordered a tube of live hookworm on the internet, | 0:26:47 | 0:26:51 | |
'and placed them on his skin, where they burrowed in, | 0:26:51 | 0:26:55 | |
'eventually finding their way into his guts. | 0:26:55 | 0:26:58 | |
'That was two years ago.' | 0:26:59 | 0:27:01 | |
Do you have any fear of food at the moment? | 0:27:01 | 0:27:03 | |
No, I mean, I'm really free, like, thanks to the worms. | 0:27:03 | 0:27:08 | |
THEY LAUGH | 0:27:08 | 0:27:10 | |
I am basically free to eat as anyone else would. | 0:27:10 | 0:27:13 | |
'Daniel's story is fascinating, | 0:27:14 | 0:27:17 | |
'but to prove that hookworm treatment works, | 0:27:17 | 0:27:20 | |
'you need proper clinical trials. | 0:27:20 | 0:27:22 | |
'Without that evidence, Helena Helmby, like most scientists, | 0:27:22 | 0:27:27 | |
'finds the idea of self-infection very troubling.' | 0:27:27 | 0:27:31 | |
I mean, scientists have worked now for over 100 years | 0:27:31 | 0:27:34 | |
trying to eradicate these diseases, and now we want to start | 0:27:34 | 0:27:37 | |
reintroducing them into people again. | 0:27:37 | 0:27:40 | |
I mean, these worms actually live in the gut and they suck blood | 0:27:40 | 0:27:45 | |
from your intestinal mucosa. | 0:27:45 | 0:27:47 | |
And they move around a lot as they do that, | 0:27:47 | 0:27:49 | |
so they cause a lot of bleeding. | 0:27:49 | 0:27:51 | |
And if you have a high dose of hookworm in your gut, | 0:27:51 | 0:27:53 | |
you will become anaemic quite quickly. | 0:27:53 | 0:27:56 | |
Rather than infecting people with human parasites, | 0:27:56 | 0:28:00 | |
we should be really looking into | 0:28:00 | 0:28:02 | |
purifying these molecules that the worms produce, | 0:28:02 | 0:28:05 | |
and turn them into drugs. | 0:28:05 | 0:28:07 | |
Turn them into worm pills. | 0:28:07 | 0:28:09 | |
So parasites can teach us a great deal about our own bodies. | 0:28:11 | 0:28:15 | |
And they may even hold the key to future medical treatments. | 0:28:17 | 0:28:20 | |
Human parasites are a reminder that | 0:28:21 | 0:28:25 | |
we are just one part of a complex web of life | 0:28:25 | 0:28:28 | |
that has evolved with us, | 0:28:28 | 0:28:31 | |
making us who we are. | 0:28:31 | 0:28:33 |