How Parasites Commandeer and Change Our Neurocircuits | Kathleen McAuliffe

Parasites are more than dormant feeders. Microscopic science is uncovering the ways viruses and bacteria prey on their hosts, influencing them to behave in some very strange ways. Kathleen McAuliffe's book is This Is Your Brain on Parasites: How Tiny Creatures Manipulate Our Behavior and Shape Society: goo.gl/ABWKvg
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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.