How Parasites Commandeer and Change Our Neurocircuits | Kathleen McAuliffe

How Parasites Commandeer and Change Our Neurocircuits | Kathleen McAuliffe

We know that parasites can make us sick, of
course, and siphon off our nutrients, but it’s very surprising to hear that some of
them, in fact there may be a large number, at least a hundred are known about at this
point in time manipulate the behavior of their host in order to enhance their own transmission. And the best way to understand this phenomenon
I think is with an example. And one is a cat parasite called Toxoplasma
Gondii or just Toxoplasma for short. I first learned about this parasitic manipulation
while just reading about scientific research and I came across a study that showed that
rodents that are infected with this parasite, they can pick up the parasite from the ground. Cats defecate this parasite so rodents as
they are scavenging around can pick up the parasite and it then invades their brain and
it actually tinkers with the animal’s neural circuits in such a fashion that it makes it
attracted to the scent of cat urine. And when I say attracted I mean sexually attracted. The rodents become sexually aroused by the
scent of cat urine so they approach and needless to say they’re not long for this world they
soon end up in the belly of a cat and that’s the only place where this parasite can sexually
replicate. So that’s its little trick. And it does many other things as well. For example, the same parasite goes to the
testicles and jacks up production of the sex hormone testosterone. In females, by means nobody’s figured out
yet, it can increase the level of the sex hormone progesterone. And in both cases these changes make the rodent
more embolden and cause the rodent to sort of lower its guard and to act in foolish ways
around cats. So that’s yet another example of other tricks
it has for getting back into the belly of a cat. This parasite can also infect us. One of the ways we can get it is changing
a cat’s litter box. And the current thinking in medicine is that
the parasite it mainly poses a threat to a developing fetus and can harm the developing
baby’s nervous system or even cause blindness. And it’s also well known to be a threat to
people who are immuno-compromised, so for example, people who have received transplanted
organs or being treated with chemotherapy. And it’s still assumed that for most healthy
people it poses no threat that once the parasite gets inside the brain that I just hunkers
down inside neurons never again to cause any problems. But there’s now several labs, both in Europe
and the United States that are challenging that dogma. And they have uncovered a lot of evidence
that for a small percentage of people the dormant infection may indeed have adverse
consequences. Nobody yet has a handle on what percentage
but about 20 percent of all Americans are infected with the parasite. So people’s guess is that we’re only talking
about a small percentage of people who have these adverse responses. But among other things it’s a link to mental
illness. So people with schizophrenia, for example,
they are two to three times more likely to have antigens against the parasite. It’s also been linked to manic depression
and it’s been linked to suicide. There was actually a study done in 22 nations
in Europe and the researchers found that suicide increased in direct proportion to the prevalence
of the parasite in each country. And it’s been a link to dangerous driving. Several studies in a few different countries
have shown that people who test positive for the parasite are more likely to be in car
accidents. So one theory, nobody knows for sure why what
the reason for this association is, but one theory is that just as rodents lower their
guard behave in a cocky way maybe people behind the wheel of a car are less vigilant. Or there’s also research that shows that infected
people have slightly slower reaction times so that’s perhaps another factor that may
influence their driving. I should emphasize these are all correlational
studies, but as scientists have learned more about what this parasite does to the rodent
brain it does make them think it’s plausible that the dormant infection is indeed causing
trouble for some individuals. There are many amazing examples of parasites
in nature that are manipulating behavior. One of my favorite examples is a parasitic
barnacle. Suspend any preconceived notions you have
about barnacles because this of barnacle is very iconoclastic; it doesn’t have a shell;
it doesn’t attach to the sides of peers or to rocks. It’s free-living during one phase of its lifecycle,
which at that point it can alight on a crab and inject a small clump of its cells into
the crab. And those cells then grow into a tangle of
root like structures and these roots wrap around all the crab’s internal organs and
eventually even sterilize the crab. And where the crab would normally grow a brood
pouch on the bottom of its belly to incubate it’s young, the parasitic barnacle pushes
out of the crab and grows a brood pouch of its own. And from that moment forward this crab lives
and exists solely to feed the parasite and to take care of it’s young. It waffs oxygen rich water around the brood
pouch to keep the parasite’s offspring well oxygenated. And then when its young are ready to be born
the crab then goes into deeper water and bobs up and down and releases the parasite’s babies
into the currents were they then go off into the world only to commandeer the minds and
bodies of more crabs. I mean to me this is the closest real life
thing to a body snatcher, science fiction’s idea of a body snatcher. I even call them robocrabs because they are
basically like an amphibious robot controlled by this parasitic barnacle. There is many other great examples in nature. Another one that I think is very impressive
is a parasitic wasp and it will grab hold of an Orb spider and attach its egg to the
abdomen of the spider. And then as this egg hatches into a larva
the larva secretes all kinds of chemicals that effectively instruct the spider to build
it a nursery. So the spider abandons its normal weaving
pattern, it stops making that sort of classic circular motif and instead creates a sort
of hammock like structure for the parasitic wasp’s larva and the larva actually attach
to the center of this net. And the spider even weaves a sort of decorative
motif around the parasite to protect it from its own enemies. It’s something even think fundamental as how
a spider weaves can be radically changed by these parasitic wasps. And there’s at least a dozen of them and they
all induce completely different kinds of webs. So that’s one example of I think a really
impressive example of a parasitic manipulation. There is a parasitic worm that gets into killifish,
it’s a very common fish found in California esrines, and it invades the fish’s brain and
the fish as a result rise to the surface and flip over on their sides and basically waive
their fins at predatory birds that are circling overhead, which that needless to say swoop
down and eat the fish. And the parasitized fish are much, much more
likely to be caught by birds, at least four times more likely to be caught. And what the parasitic worm appears to do
is it acts on parts of the brain that are controlled by serotonin, the neurotransmitter
serotonin. And the infected fish seem normal and healthy
in every single way except they’re much more mellow. They’re like a fish on Prozac. So that’s how that manipulation works. Another manipulation that actually makes me
shudder when I even think about it, it’s a fungus. And what happens is ants as they’re on the
forest floor they may pick up a spore of this fungus from the ground and there is nothing
domicile about this fungus because as soon as it attaches to the ant it burrows into
the ant and it starts rapidly growing. And as it’s doing this it instructs the ant
at exactly solar noon to go to the nearest sapling to climb exactly one foot above the
ground to go to the northwestern a part of the plant, lock onto the main vein of the
leaf and then this fungus, and this is the part of the creeps me out, like sprouts from
the ant’s head and it grows this long stock. And at the tip of the stock is this fruiting
body that then explodes and rains spores down on more ants that are walking along the forest
floor below.

11 thoughts on “How Parasites Commandeer and Change Our Neurocircuits | Kathleen McAuliffe”



  2. Thank you for the parasite audiobook series as it is very informative and interesting. I am wondering if you would be able to help me determine if the 165 degree temperature suggested when cooking meat is hot enough to kill all living parasites and their eggs, especially the pork tapeworm, their eggs and cysts. I have heard the temperature needed to kill all pork tapeworm stages is 500 degrees which would destroy the meat totally. It has also been said that freezing for varying lengths of time will kill all stages. I realize that the pork tapeworm resides in many other animals including man where it is responsible for epileptic seizures.

  3. Humans also have social parasites who siphon off the fruits of our labors for their own purposes. How do we cure that one?

  4. So what's the point of this video, is there a solution that she offers other than getting rid of our cat's, because that's not going to happen. She also fails to mention that not all cats have this parasites. What about dogs who are notorious for having parasite. When I was a kid we had a crazy dog who chased cars and use to scoot across the carpet. We were poor and this poor dog clearly suffered from parasites but was never taken to see a vet. I'm almost 60 and have suffered for years from unexplained illness that the countless doctors I be saw had no answers for. I remembered how that dog behaved and tried to convince my doctors that I had parasites which I believed was the source of my unexplained illiness. They tried to convince me I was wrong, but I follow my gut and turned out I was full of parasites, from that DOG from years ago. I've only been on my parasite journey for about a year but my health is greatly improved. Bottom line most animals probably harbor parasite so why just speak about cats.🤔

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