Is there a disease that makes us love cats? - Jaap de Roode
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0:07 - 0:10Is there a disease
that makes us love cats, -
0:10 - 0:12and do you have it?
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0:12 - 0:14Maybe,
-
0:14 - 0:16and it's more likely than you'd think.
-
0:16 - 0:18We're talking about toxoplasmosis,
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0:18 - 0:23a disease caused by toxoplasma gondii.
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0:23 - 0:27Like all parasites, toxoplasma lives
at the expense of its host, -
0:27 - 0:30and needs its host to produce offspring.
-
0:30 - 0:35To do that, toxo orchestrates a brain
manipulation scheme -
0:35 - 0:36involving cats,
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0:36 - 0:38their rodent prey,
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0:38 - 0:41and virtually all other birds and mammals,
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0:41 - 0:43including humans.
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0:43 - 0:48Documented human infections go as far back
as ancient Egypt. -
0:48 - 0:51We found samples in mummies.
-
0:51 - 0:54Today, about a third of the world's
population is infected, -
0:54 - 0:57and most of them never even know it.
-
0:57 - 1:01In healthy people, symptoms often
don't show up at all. -
1:01 - 1:04When they do, they're mild and flu-like.
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1:04 - 1:07But those are just the physical symptoms.
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1:07 - 1:10Toxoplasma also nestles into our brains
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1:10 - 1:14and meddles with our behavior
behind the scenes. -
1:14 - 1:19To understand why, let's take a look
at the parasite's life cycle. -
1:19 - 1:23While the parasite can multiply
in practically any host, -
1:23 - 1:27it can only reproduce sexually
in the intestines of cats. -
1:27 - 1:32The offspring, called oocysts,
are shed in the cat's feces. -
1:32 - 1:36A single cat can shed up to
a hundred million oocysts. -
1:36 - 1:41If another animal, like a mouse,
accidentally ingests them, -
1:41 - 1:45they'll invade the mouse's tissues
and mature to form tissue cysts. -
1:45 - 1:48If the mouse gets eaten by a cat,
-
1:48 - 1:51the tissue cysts become active
and release offspring -
1:51 - 1:54that mate to form new oocysts,
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1:54 - 1:56completing the cycle.
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1:56 - 1:57But there's a problem.
-
1:57 - 2:01A mouse's natural desire to avoid
a cat makes it tough to close this loop. -
2:01 - 2:05Toxoplasma has a solution for that.
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2:05 - 2:10The parasites invade white blood cells
to hitch a ride to the brain -
2:10 - 2:14where they seem to override the innate
fear of predators. -
2:14 - 2:19Infected rodents are more reckless
and have slower reaction times. -
2:19 - 2:24Strangest of all, they're actually
attracted to feline urine, -
2:24 - 2:28which probably makes them more likely
to cross paths with a cat -
2:28 - 2:31and help the parasite
complete its life cycle. -
2:31 - 2:34How does the parasite pull this off?
-
2:34 - 2:39Although the exact mechanism isn't known,
toxo appears to increase dopamine, -
2:39 - 2:44a brain neurotransmitter that is involved
in novelty-seeking behavior. -
2:44 - 2:49Thus, one idea is that toxo tinkers
with neurotransmitters, -
2:49 - 2:52the chemical signals
that modulate emotions. -
2:52 - 2:53The result?
-
2:53 - 2:55Fatal attraction.
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2:55 - 2:59But mice aren't the only animals
that end up with these parasites, -
2:59 - 3:04and that's where humans,
and all of toxo's other hosts, come in. -
3:04 - 3:09We can accidentally ingest oocysts
in contaminated water, -
3:09 - 3:11or unwashed produce,
-
3:11 - 3:13or from playing in sandboxes,
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3:13 - 3:15or cleaning out litter boxes.
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3:15 - 3:21This is behind the common recommendation
that pregnant women not change cat litter. -
3:21 - 3:24Toxo can cause serious birth defects.
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3:24 - 3:27We can also get toxo
from eating undercooked meat -
3:27 - 3:31from other animals that picked up
some oocysts. -
3:31 - 3:34And it turns out that toxo can mess with
our brains, too. -
3:34 - 3:38Studies have found connections between
toxo and schizophrenia, -
3:38 - 3:40biopolar disorder,
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3:40 - 3:42obsessive compulsive disorder,
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3:42 - 3:44and aggression.
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3:44 - 3:47It also slows reactions
and decreases concentration, -
3:47 - 3:52which may be why one study found
that people involved in traffic accidents -
3:52 - 3:57were almost three times more likely
to have toxoplasma. -
3:57 - 4:02So is toxo manipulating our brains
as an evolutionary strategy -
4:02 - 4:06to get predatory cats to eat us?
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4:06 - 4:09Or are our brains just similar enough
to a rodent's -
4:09 - 4:15that the same neurological tricks that
lure them in catch us in the net, too? -
4:15 - 4:21And is toxo the reason so many people
love cats and keep them as pets? -
4:21 - 4:24Well, the jury's still out on that one.
-
4:24 - 4:27Some recent studies
even contradict the idea. -
4:27 - 4:31Regardless, toxoplasma has definitely
benefited from humans -
4:31 - 4:34to become one of the world's
most successful parasites. -
4:34 - 4:38It's not just our willingness to let
cats on our dining room tables -
4:38 - 4:40or in our beds.
-
4:40 - 4:43Raising livestock
and building cities which attract rodents -
4:43 - 4:45has provided billions of new hosts,
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4:45 - 4:50and you and your cat may be two of them.
- Title:
- Is there a disease that makes us love cats? - Jaap de Roode
- Description:
-
View full lesson: http://ed.ted.com/lessons/is-there-a-disease-that-makes-us-love-cats-jaap-de-roode
Today, about a third of the world’s population is infected with a strange disease called toxoplasmosis — and most of them never even know it. And while the parasite can multiply in practically any host, it can only reproduce sexually in the intestines of cats. Could this disease be the reason so many people love cats and keep them as pets? Jaap de Roode shares what we know about toxoplasmosis.
Lesson by Jaap de Roode, animation by Anton Bogaty.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 05:06
Brian Greene edited English subtitles for Is there a disease that makes us love cats? - Jaap de Roode | ||
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Jessica Ruby edited English subtitles for Is there a disease that makes us love cats? - Jaap de Roode | ||
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