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"Toxoplasma gondii." That's the fancy name for it. "Toxo" is its shortened nickname. You've probably never heard of it, but odds are you've probably got it.
This is not some deadly disease that's going to turn you into a zombie or some other marauder. Toxo is a parasite that normally makes its home in rats, but it actually breeds more of its own kind in the belly of cats. Sounds weird, right? Toxo is insidious in its nature. It works its way into the brains of the rats, essentially making the rats think the cats look quite attractive. The rat basically becomes suicidal, placing itself in positions where it can actually attract the cat's attention. The cat does what comes naturally to it, of course. The result is a dead rat, a well-fed cat, and a parasite that is now transferred from host to incubator.
The traditional thinking was that Toxo was not a real problem for any human who happened to pick it up. If a person had an impaired immune system, the parasite's presence could cause complications. But, for the most part, healthy adults who contracted the parasite would experience flu-like symptoms for a short period of time. The body would fight off the parasite, the parasite would be forced into a dormant state, and there it would remain, doing no harm and going unnoticed.
That used to be the school of thought on the matter, anyway.
This is Jaroslav Flegr. He is a Czech scientist who is responsible for most of the body of information we have on Toxoplasma gondii. Flegr started to study the parasite after recognizing that he was actually exhibiting behaviors that he observed in many of the other species who were being influenced by a parasite infestation. These behaviors included recklessness and disregard for safety. Flegr began to study Toxo and its life cycle, and when he was able to have it done, he had himself tested. He discovered he was, indeed, infected.
In the United States and Europe, it is estimated that approximately half of the human population may be infected with Toxo. People can become infected by coming in contact with litter boxes used by cats who venture outdoors. Cats obtain the parasite by killing infected rodents. But the cats aren't the only ones to blame. This parasite can live in the soil before it attaches itself to a rat. This means you can also become infected by eating unwashed vegetables.
When a rat or other small creature becomes infested with Toxo, the parasite finds its way to the host's brain. Here it effectively "rewires" the rat's brain to ignore its natural fear of predators like cats. The parasite wants the host to be eaten by a cat. So it alters the rat's behavior, making it bolder and more tolerant of risky behavior. It also makes the rat find the scent of cat urine attractive. Once the cat kills the rat, the Toxo is transferred to the new host, the cat, and the cycle begins anew.
No one disputed the effect of Toxo on rats. With the exception of the attraction to cat urine, Flegr observed some of his own behaviors were similar to those of the infested rats. He set up experiments to test his hypothesis. Using test subjects that were and were not infected, he found that men who were infected were more likely to be introverted, suspicious, unconcerned with the opinions others held of them, and more likely to disregard rules. Infected women were more like to exhibit opposite behaviors. They were more extroverted, trusting, conscious of their images, and more rule-abiding than their uninfected counterparts. As strange as it sounds, Flegr was able to replicate the results across all societal spectrums.
Flegr continued his research, turning up some rather disturbing data. Other researchers began to take notice of his work. Flegr's studies uncovered a link between higher incidences of traffic accidents and Toxo infection. He believes this is a result of a lowered fear response; a result of the parasite's influence. He is now investigating a possible link between Toxo infestation and schizophrenia. One of the long-term results of schizophrenia is a reduction in the brain's gray matter. According to preliminary studies, Toxo may be to blame. Flegr suspects that a Toxo infection can possibly trigger schizophrenia in those who carry a genetic predisposition to the illness. There is no empirical evidence to support that theory; not as yet, anyway.
There's no reason to think that Toxo infestation is going to bring on the equivalent of a zombie apocalypse. Infection rates in the United States are significantly lower than in other countries. In the U.S., it is estimated that 10% to 20% of the population may be infected, compared to up to 55% in France, Czech Republic with 30% to 40%, and the incidence of infection may be as high as 95% in parts of the developing world.
There is, unfortunately, no effective treatment for Toxo at this time. Once infested, the parasite is there to stay. That doesn't mean you should immediately get rid of your beloved cats. It is only outdoor cats who are prone to bring Toxo into your home. An outdoor cat typically only sheds Toxo for about three weeks when they're young. Flegr advises protective measures such as keeping kitchen counters clean, thoroughly washing all vegetables and fruits, and avoiding improperly purified water.
Moral of the story: keep your cat's litter boxes clean, keep your home clean, and wash all fruits and vegetables before consuming. Simple, common sense measures that can keep your brain parasite-free.