Half The Human Population Is Infected!

Are brain parasites altering the personalities of three billion people? The question emerged a few years ago, and it shows no signs of going away.

I first encountered this idea while working on my book Parasite Rex. I was investigating the remarkable ability parasites have to manipulate the behavior of their hosts. The lancet fluke Dicrocoelium dendriticum, for example, forces its ant host to clamp itself to the tip of grass blades, where a grazing mammal might eat it. It’s in the fluke’s interest to get eaten, because only by getting into the gut of a sheep or some other grazer can it complete its life cycle. Another fluke, Euhaplorchis californiensis, causes infected fish to shimmy and jump, greatly increasing the chance that wading birds will grab them.

Those parasites were weird enough, but then I got to know Toxoplasma gondii. This single-celled parasite lives in the guts of cats, sheddding eggs that can be picked up by rats and other animals that can just so happen be eaten by cats. Toxoplasma forms cysts throughout its intermediate host’s body, including the brain. And yet a Toxoplasma-ridden rat is perfectly healthy. That makes good sense for the parasite, since a cat would not be particularly interested in eating a dead rat. But scientists at Oxford discovered that the parasite changes the rats in one subtle but vital way.

The scientists studied the rats in a six-foot by six-foot outdoor enclosure. They used bricks to turn it into a maze of paths and cells. In each corner of the enclosure they put a nest box along with a bowl of food and water. On each the nests they added a few drops of a particular odor. On one they added the scent of fresh straw bedding, on another the bedding from a rat’s nests, on another the scent of rabbit urine, on another, the urine of a cat. When they set healthy rats loose in the enclosure, the animals rooted around curiously and investigated the nests. But when they came across the cat odor, they shied away and never returned to that corner. This was no surprise: the odor of a cat triggers a sudden shift in the chemistry of rat brains that brings on intense anxiety. (When researchers test anti-anxiety drugs on rats, they use a whiff of cat urine to make them panic.) The anxiety attack made the healthy rats shy away from the odor and in general makes them leery of investigating new things. Better to lie low and stay alive.

Then the researchers put Toxoplasma-carrying rats in the enclosure. Rats carrying the parasite are for the most part indistinguishable from healthy ones. They can compete for mates just as well and have no trouble feeding themselves. The only difference, the researchers found, is that they are more likely to get themselves killed. The scent of a cat in the enclosure didn’t make them anxious, and they went about their business as if nothing was bothering them. They would explore around the odor at least as often as they did anywhere else in the enclosure. In some cases, they even took a special interest in the spot and came back to it over and over again.
The scientists speculated that Toxoplasma was secreted some substance that was altering the patterns of brain activity in the rats. This manipulation likely evolved through natural selection, since parasites that were more likely to end up in cats would leave more offpsring.

The Oxford scientists knew that humans can be hosts to Toxoplasma, too. People can become infected by its eggs by handling soil or kitty litter. For most people, the infection causes no harm. Only if a person’s immune system is weak does Toxoplasma grow uncontrollably. That’s why pregnant women are advised not to handle kitty litter, and why toxoplasmosis is a serious risk for people with AIDS. Otherwise, the parasite lives quietly in people’s bodies (and brains). It’s estimated that about half of all people on Earth are infected with Toxoplasma.

Given that human and rat brains have a lot of similarities (they share the same basic anatomy and use the same neurotransmitters), a question naturally arose: if Toxoplasma can alter the behavior of a rat, could it alter a human? Obviously, this manipulation would not do the parasite any good as an adaptation, since it’s pretty rare for a human to be devoured by a cat. But it could still have an effect.

8 comments

  • must be the source of psychopathy in humans (the brain addled elite)

  • Liberal progressives and their affinity toward the ‘European Model’ explained

  • far more things affect how people behave. Like what neuroprogramming is influenced by the particular social and informational physical environment you live in; and what tendencies your mind has learned to depend on for solving the problems you encounter, for example. In fact it would blow your mind to know each and every one of them; because people in that frame of understanding are actually no longer people, but systems. Everything, from TV to emotional & psychological crutches to the very fact humans don’t consciously evaluate all their options for spending each day, and right down to the air pressure and temperature and layout of a room and how many people have access to it, influences exactly what/who you yourself are; why you are this way in particular. Destiny is simply defined as how all of these things like traffic systems and like financial trades and all the rest of it converge onto influencing individual systems we call human beings (and falsely attribute/ascribe to, the status of independently-acting “personalities”).

    So yeah when people take on a new infection they are altered, but it’s the same for a new grudge or worldview or whatever. Ultimately it’s just as difficult to be able to pin down or isolate, something to judge or quantify something by; some individual action or effect. Knowing a previously unidentified/unseen illness such as discussed in the article might help, but there are already plenty of ills in society to identify! For example, we might discuss emotional needs not being met in everyday society, which opens up opportunities for a predatory advertising system to benefit..

    • Idk what you’re saying, i think that the point is IF humans COULD be controlled via a parasitic” clingon ie toxoplasmosis, would we know it? Joe rogan says all Brazilians are infected with toxoplasmosis, the effects, he has claimed, induce animal instinct ie: men are territorial to a high degree and women are more horny. If Joe’s to be believed, idk why we wouldn’t, toxoplasmosis HAS infected humans in a controlling way. I guess ponder taken hold its aim is to multiply and spread… What better way than fighting (blood borne infections) and fucking in order to spread

      • That sounds believable enough

        My point was that there are also many other “undiagnosed” conditions of the human psyche and human behaviour itself. For example, we only hear objective arguments surrounding our use of the planet through ecological study; otherwise it’s a social item of opinion ultimately driven by very complex interactions throughout our society.. essentially meaning we never “see the obvious”. Point being.. that there are many more things we ought to consider– not just effects we label as non-traditionally-human (separate from psychology and the body) !!

      • I’m offensive and find Joe’s comment very Brazilian.
        (Seriously, don’t say “all” Brazilians, there are different people around here).

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s