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Is there a disease that makes us love cats? - Jaap de Roode

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    Is there a disease
    that makes us love cats,
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    and do you have it?
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    Maybe,
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    and it's more likely than you'd think.
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    We're talking about toxoplasmosis,
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    a disease caused by toxoplasma gondii.
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    Like all parasites, toxoplasma lives
    at the expense of its host,
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    and needs its host to produce offspring.
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    To do that, toxo orchestrates a brain
    manipulation scheme
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    involving cats,
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    their rodent prey,
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    and virtually all other birds and mammals,
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    including humans.
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    Documented human infections go as far back
    as ancient Egypt.
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    We found samples in mummies.
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    Today, about a third of the world's
    population is infected,
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    and most of them never even know it.
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    In healthy people, symptoms often
    don't show up at all.
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    When they do, they're mild and flu-like.
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    But those are just the physical symptoms.
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    Toxoplasma also nestles into our brains
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    and meddles with our behavior
    behind the scenes.
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    To understand why, let's take a look
    at the parasite's life cycle.
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    While the parasite can multiply
    in practically any host,
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    it can only reproduce sexually
    in the intestines of cats.
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    The offspring, called oocysts,
    are shed in the cat's feces.
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    A single cat can shed up to
    a hundred million oocysts.
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    If another animal, like a mouse,
    accidentally ingests them,
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    they'll invade the mouse's tissues
    and mature to form tissue cysts.
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    If the mouse gets eaten by a cat,
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    the tissue cysts become active
    and release offspring
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    that mate to form new oocysts,
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    completing the cycle.
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    But there's a problem.
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    A mouse's natural desire to avoid
    a cat makes it tough to close this loop.
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    Toxoplasma has a solution for that.
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    The parasites invade white blood cells
    to hitch a ride to the brain
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    where they seem to override the innate
    fear of predators.
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    Infected rodents are more reckless
    and have slower reaction times.
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    Strangest of all, they're actually
    attracted to feline urine,
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    which probably makes them more likely
    to cross paths with a cat
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    and help the parasite
    complete its life cycle.
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    How does the parasite pull this off?
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    Although the exact mechanism isn't known,
    toxo appears to increase dopamine,
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    a brain neurotransmitter that is involved
    in novelty-seeking behavior.
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    Thus, one idea is that toxo tinkers
    with neurotransmitters,
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    the chemical signals
    that modulate emotions.
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    The result?
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    Fatal attraction.
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    But mice aren't the only animals
    that end up with these parasites,
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    and that's where humans,
    and all of toxo's other hosts, come in.
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    We can accidentally ingest oocysts
    in contaminated water,
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    or unwashed produce,
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    or from playing in sandboxes,
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    or cleaning out litter boxes.
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    This is behind the common recommendation
    that pregnant women not change cat litter.
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    Toxo can cause serious birth defects.
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    We can also get toxo
    from eating undercooked meat
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    from other animals that picked up
    some oocysts.
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    And it turns out that toxo can mess with
    our brains, too.
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    Studies have found connections between
    toxo and schizophrenia,
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    biopolar disorder,
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    obsessive compulsive disorder,
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    and aggression.
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    It also slows reactions
    and decreases concentration,
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    which may be why one study found
    that people involved in traffic accidents
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    were almost three times more likely
    to have toxoplasma.
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    So is toxo manipulating our brains
    as an evolutionary strategy
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    to get predatory cats to eat us?
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    Or are our brains just similar enough
    to a rodent's
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    that the same neurological tricks that
    lure them in catch us in the net, too?
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    And is toxo the reason so many people
    love cats and keep them as pets?
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    Well, the jury's still out on that one.
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    Some recent studies
    even contradict the idea.
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    Regardless, toxoplasma has definitely
    benefited from humans
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    to become one of the world's
    most successful parasites.
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    It's not just our willingness to let
    cats on our dining room tables
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    or in our beds.
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    Raising livestock
    and building cities which attract rodents
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    has provided billions of new hosts,
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    and 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.

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Video Language:
English
Team:
closed TED
Project:
TED-Ed
Duration:
05:06

English subtitles

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