Odds Are, You’re Probably Infected With This Brain Parasite And Don’t Even Know It

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at 2015.10.13
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Have you heard of Toxoplasma gondii, or Toxo for short? Chances are you probably haven”t. Chances are you”re probably infected with it.

Don”t worry, it”s not a deadly disease, but it is insidious in its own way. Toxo is a parasite that”s traditionally found in rats, but breeds inside the stomachs of cats. It does this by subtly rewiring rats” brains to be attracted to cats. The rat then willingly puts itself in harm”s way for a cat to kill and eat it, thus transferring the parasite to the cat.

Traditional thinking was that while humans can contract Toxo, it”s no real threat to us. In those with impaired immune systems, the parasite can sometimes cause complications. However, for healthy adults, infection results in a short flu-like sickness while the body fights off the parasite. It then proceeds to lay dormant inside the brain.

Well at least that used to be what we thought…

Meet Czech scientist Jaroslav Flegr. Most of what we know about Toxo comes from his research.

Meet Czech scientist Jaroslav Flegr. Most of what we know about <em>Toxo </em>comes from his research.

It sounds strange, but Flegr began studying Toxo after recognizing that some of his behaviors in many ways mimicked that of other species whose brains were being manipulated by parasites (recklessness, disregard for his own safety). After the fall of Communism, Flegr began to dedicate himself to the of study Toxo and its lifecycle. Eventually, he had himself tested for it, and it turns out he was infected.

It”s estimated that around half the human population is infected with Toxo, it”s actually pretty easy to contact.


In the United States and Europe, many people become infected with Toxo by coming into contact with the litter boxes of outdoor cats. Cats pick up the parasite by killing infected rodents when they hunt. But cat lovers aren”t the only ones who have to worry about contracting Toxo. Because the organism lives in the soil before it”s picked up by rats, you can also contract it by eating unwashed vegetables.

So what does Toxo do exactly?

So what does <em>Toxo</em> do exactly?

When rats and other small rodents contract Toxo, essentially the parasite rewires parts of the rats” brain to make them attractive targets to be killed by cats. It makes the rats bolder and more tolerable of risk. It also makes them attracted to the scent of cat urine. Toxo does this by essentially rerouting dopamine (the reward hormone) in the rat”s brain. Then once the cat kills the rat, Toxo jumps hosts and the cycle begins again.

Alright, so Toxo is bad news for rats, but what about humans? That”s the question Flegr set out to answer.

Alright, so <em>Toxo </em>is bad news for rats, but what about humans? That

Flegr recognized some of his own behaviors as similar to those of rats infected with Toxo (minus the attraction to cat urine), but could those just be a coincidence? So he set up experiments with various participants who both had and did not have Toxo. What he found was that infected men were more introverted, suspicious, oblivious to people”s opinions of them, and inclined to disregard rules. While infected women were much the opposite. They were more outgoing, trusting, image-conscious, and rule-abiding than uninfected women. These results sound strange, but Flegr was able to replicate them over and over again across all areas of society.

As Flegr continued his Toxo research he began to find evidence of some pretty disturbing things and other research institutes began to take notice…

As Flegr continued his <em>Toxo </em>research he began to find evidence of some pretty disturbing things and other research institutes began to take notice...

One study Flegr conducted linked Toxo infection with a higher likelihood of traffic accidents. He attributes this to the parasite lowering the normal fear response. These days Flegr is looking into a possible link between Toxo infection and schizophrenia. One of the long term symptoms of schizophrenia is a reduction in gray brain matter and according to prelimary studies, Toxo is to blame. While it has yet to be empirically proven, Flegr believes that Toxo infection can actually trigger schizophrenia in those who are genetically predisposed to the illness.

The big question is though, should we start panicking about Toxo?

The big question is though, should we start panicking about <em>Toxo</em>?

Probably not. Infection rates in America are markedly lower than in other parts of the world. (Only 10 to 20 percent versus up to 55 percent in France, 30 to 40 percent in the Czech Republic, and up to 95 percent in parts of the developing world.) Also, and here”s the bad news, there”s no effective treatment for eradicating Toxo in humans once you”re infected. So even if you”re infected, you can”t really do anything about it.

(via: The Atlantic)

But don”t get rids of your cats just yet if you”re looking to avoid getting Toxo. It”s only outdoor cats who are prone to bringing Toxo into the home. If you do have outdoor cats, Flegr says that they typically only shed Toxo for three weeks when they”re young. Flegr advises keeping kitchen surfaces clean, thoroughly washing all vegetables, and avoiding water that hasn”t been properly purified.

I”m very uncomfortable with the idea of a prehistoric parasite inadvertently infecting me, then subtly influencing my thoughts and actions, but at the time same time, I think I”d rather not know if I”m infected with Toxo. In this particular area of life I think that ignorance really is bliss.

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