Toxoplasma Sexes Up Rats Brains

A couple of years ago I became aware of the very intriguing virus Toxoplasma Gondii.  I say “intriguing” because of how it goes about its life cycle, and the unique way it influences hosts into strange behavior.

Just about every organism that this virus infects receives a behavior modification that is beneficial to the virus, and mostly detrimental to its host.  Its great limit is that it cannot reproduce unless it is in a cat’s gut, and this is where the following article picks up:

When a male rat senses the presence of a fetching female rat, a certain region of his brain lights up with neural activity, in anticipation of romance. Now Stanford University researchers have discovered that in male rats infected with the parasite Toxoplasma, the same region responds just as strongly to the odor of cat urine.

Is it time to dim the lights and cue the Rachmaninoff for some cross-species canoodling?

“Well, we see activity in the pathway that normally controls how male rats respond to female rats, so it’s possible the behavior we are seeing in response to cat urine is sexual attraction behavior, but we don’t know that,” said Patrick House, a PhD candidate in neuroscience in the School of Medicine. “I would not say that they are definitively attracted, but they are certainly less afraid. Regardless, seeing activity in the attraction pathway is bizarre.”

For a rat, fear of cats is rational. But a cat’s small intestine is the only environment in which Toxoplasma can reproduce sexually, so it is critical for the parasite to get itself into a cat’s digestive system in order to complete its lifecycle.

Thus it benefits the parasite to trick its host rat into putting itself in position to get eaten by the cat. No fear, no flight — and kitty’s dinner is served.


The fact that rats infected with toxoplasma tended to not fear cat is not newly known.  It is what really intrigued me to begin with.  The method by which it is done, however, is most sinister.  Sexual urge is the most carnal of desires, and the most primitive.  The manipulation by this virus of the grey matter of the rat, shortening its life on purpose by causing it to have a sexual attraction to a VERY risky behavior, is quite nefarious.

Like I said, it was this initial ability to modify the behavior of an animal that interested me, especially since up to 80% of the population may be infected with it.  What types of behaviors might this virus be causing?  Could it be why we find ourselves attracted to cats as pets?

Well, it may be more drastic than that.

Findings from what is believed to be the largest comparison of blood samples collected from healthy individuals and people with schizophrenia suggest that infection with the common Toxoplasma gondii parasite, carried by cats and farm animals, may increase the risk of schizophrenia.

Researchers found that of the 180 study subjects diagnosed with schizophrenia, 7 percent had been infected with toxoplasma prior to their diagnosis, compared to 5 percent among the 532 healthy recruits. Thus, people exposed to toxoplasma had a 24 percent higher risk of developing schizophrenia. The difference, while seemingly small, is important, researchers say, because the ability to explain even a small portion of the 2 million cases of schizophrenia in the United States may offer clues to the disease and some possible treatments.

For example, the investigators say they plan to study whether aggressive treatment of toxoplasma infection with antiparasitic drugs in patients with schizophrenia could halt the progression of the mental disorder, characterized by paranoia, delusions and hallucinations.

Most infections with toxoplasma occur early in life following exposure to the parasite in cat feces or undercooked beef or pork. Infections rarely cause symptoms, but the parasite remains in the body and can reactivate after lying dormant for years.


The chilling part of this is that it can lay dormant for years.  This may indicate that we have a retrovirus type viral infection, whereby the virus actually can encode itself into your DNA, and come “alive” again in the future by causing cells that it is “encoded” within to begin churning out the viral packages.

And this is what really gets me to thinking.  How much of our DNA has been gained via viral infection?  Only 1 out of every 10 cells in our body is actually us.  The rest are various bacteria and other microbes.  In essence, you are barely even you.  That seems to be an outstanding opportunity for some genetic swapping, especially when you get viruses into the equation.

Could that be what “flu like symptoms” are?  The “uploading” of this genetic material, and the subsequent spreading of these new cells (a la gene therapy)?




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