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Toxoplasma Gondii: Brain Parasite Extraordinare

Updated on February 9, 2009

The Stuff of Science Fiction

For most of the 20th century science fiction authors speculated about various methods of brain control. Would mechanical implants control us? Hypnotic suggestions? Or even, gasp, aliens? Can't we just be our own people, free to be you and me? Well, apparently the answer is no. Scientists have now discovered that a brain parasite, called toxoplasma gondii, which infects half of the human population on Earth, may alter human behavior in signicant ways.

But before we get to human beings let's start a little lower down the mammalian ladder, with two animal arch enemies, the cat and the rat.

The Feline Connection

When you boil it down to the basic facts, cats are the common denominator where toxoplasma gondii infection is concerned. The parasite is the reason why pregnant women are cautioned not to clean cat litter boxes, because exposure to the parasite can cause toxoplasmosis. In infants this can cause serious neurological defects, organ damage, or even death. But for the moment we want to focus on the cat connection.

Cats are the main repository of the disease because the organism requires a cat to enter the reproductive phase of its lifecycle. It most certainly can and does infect other animals though. One of the most profound effects of the infection occurs in rats and mice. These creatures are fearful of cat urine because it marks the presence of a predator, and a healthy rat or mouse will try to hide when presented with cat urine. In studies done on rodents infected with toxoplasma gondii however, the rodents were not afraid of the smell of cat urine. In fact, they were even drawn to it, seeking out the scent and lingering by it, even though to do so meant certain death.

Why would a rat offer up its life like this? Simply put, because the toxoplasma gondii wanted it to. The parasite needs to be eaten by a cat in order to reproduce. Most cats prefer live, fresh meat, so the parasite allows the rat to live. In order to direct the rodent to the correct place however, the toxoplasma gondii targets the place in the rodent's brain where fear of cat urine resides, and almost surgically, alters it. Talk about an intelligent organism.

Once eaten by the cat the toxoplasma reproduces in the guts of the cat. The eggs are then shed, mostly in feces, and when rats come across this they start the whole cycle all over again.

Toxoplasma Gondii and Humans

At this point scientists estimate that almost 3 billion people (half the world's population) are infected with toxoplasma gondii. The implications of this spread far beyond normal medical concerns. This is because toxoplasma is also thought to cause mental changes in humans, though not in the same way as mice.

One of the strongest connections between human mental illness and toxoplasma gondii exists in schizophrenia. Toxoplasma gondii damages astrocytes, which are the brains support cells. Damaged astrocytes are also an indicator of schizophrenia. Women who pass toxoplasma gondii on to their children also are more likely to give birth to babies who will develop schizophrenia.

It has also been found that countries with higher infection rates of toxoplasma gondii have higher neuroticism scores, which includes high levels of anxiety or depression. Toxoplasma gondii is also thought to contribute to bi-polar disorder.

Such high infection rates mean that entire cultures may have been shaped by the brain parasite. A scary thought if one really thinks about it.

When a person contracts toxoplasma gondii it may result in mild flu-like symptoms, or even be asymptomatic (without symptoms). Most people who carry the parasite are unaware. The acute stage, when the parasite is initially contracted, lasts for a few days to a few months, after which the parasite becomes latent. It stays this way unless the infected person develops problems with the immune system (like HIV) after which the person can develop toxoplasmosis.

Toxoplasma gondii emerging out from fibroblasts


Acute toxoplasmosis can be treated by a variety of antibiotics including Sulfadiazine and clindamycin. The latent parasite is much harder to kill, and it is almost impossible to eradicate all of the cysts developed by the parasite in the body. It has been found that anti-psychotics, like those used to treat schizophrenia, are also effective in killing the parasite.


So the next time someone brings up mind control, don't laugh. You never know if the person sitting next to you has a host of little friends crawling around in their brain and muscle tissue. To investigate further click on the links to the right.


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    • dallas93444 profile image

      Dallas W Thompson 

      7 years ago from Bakersfield, CA

      Great article! In researching for my book, "Eyes Wide Shut: an Enigma" I was shocked to learn what you just shared. As no noted about half us have T. gondii. There is no cure. The scary part is if your immune system is "down" T. gondii can flare-up with much worse symptoms... including death. Organ transplants, Aids and many other causes can knocked down your immune system.

      It has been discovered T. gondii (Toxoplosmosis) is in our driniking water and the oceans. Seals in Morro Bay, California are dying. Whales in the Artic have T. gondii. Seals in England have it... It is thought the anchovies are "spreading" the T. gondii parasite in the oceans. Clams, mussels infect others as well...

      T. gondii changes entire cultures. Brazil and France have a high infection rate. 70%- 90%. One of the "symptoms" of T. gondii infection for women is men are attracted to them. Women are promosicuis. Infected men take more risks... Most all motorcycle owners are infected. People in car wrecks have a high infection rates...

      There is no cure...

      They have isolated a singe protein that causes T. gondii to do its "bad" stuff." T. gondii produces naturally occurring amino acid L-3,4-dihydroxyphenylalanine (L-dopa).

      Thanks for sharing this!

      Flag up!

    • profile image

      r cortez 

      9 years ago

      if anyone,,needs info about toxo,,im not a dr,,,but i really understand the illness,,,and if i can help someone i be glad,,,had toxo,,and now recovering,,,

    • profile image

      r cortez 

      9 years ago

      i had toxo,,,and i believe, that the parasite can change human behaviour,,or behaviour shift,,,im an inmunocompetent,,but still develop severe symtoms,,,had toxo for 4 years,,without a diagnosis,,,,these is very very serious ilness and its 1000 symptoms,,,,and a slow recovery,,,,after treatment,,in the acute phase i thought i was loosing my mind,,,y thought i had catch rabies,,,,,severe depression anxiety,,,,etc etc food allergies very very tired etc etc,,,,


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