HealthWatch: Human Behavioral Change May Be Tied To Cat Parasite

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A vet examines a cat.  (Liu Jin/AFP/Getty Images)

A vet examines a cat. (Liu Jin/AFP/Getty Images)

CBS SF Bay (con't)

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STANFORD (CBS 5) – Intriguing new research finds how tiny organisms carried by cats may be causing subtle and at times dramatic changes in human behavior.

Researchers now believe something commonly carried by cats could be controlling you, a tiny parasite called Toxoplasma Gondi.

“This is a very clever parasite,” said Dr. Patricia Conrad, an expert in the parasite at the U.C. Davis School of Veterinary Medicine. Conrad added that some people consider toxoplasma to be the most successful parasite in the entire world.

The parasite can only sexually reproduce in the intestines of cats. Infected cats then excrete millions of microscopic eggs, called oocysts, in the soil, in water, and in litter boxes. That’s why pregnant women are told not to handle litter boxes.

“There is a risk that then the parasite will go from the mother to her baby,” said Dr. Jose Montoya, an expert in infectious diseases at Stanford University – as well as the Director of the Toxoplasma Serology Laboratory at the Palo Alto Medical Foundation. The Lab is the national reference lab for toxoplasmosis in the United States.

If a pregnant woman passes the parasite to her unborn child, the baby can then suffer serious brain damage, even die, explained Dr. Montoya.

But because cats poop outdoors, infected cats excrete far more oocysts into the environment. These oocysts endure for months, if not years. Many Americans who don’t own cats or handle litter boxes can get infected. They pick it up in the environment.

According to the Centers for Disease control, an estimated 60 million Americans are infected with the parasite, and they actually are chronically infected and show little ill effect.

“So it’s our immune system that really helps to control the parasite keep it in check,” explained Dr. Conrad.

But now there’s growing evidence that the parasite can creep into your brain, and directly manipulate your behavior.

“It’s a little creepy actually. It’s almost like a science fiction story but it’s probably what’s actually happening,” said Dr. Robert Yolken, an infectious disease specialist and neuro-virologist at Johns Hopkins University School of Medicine.

His research found people infected with toxoplasma were two to three times more likely to develop schizophrenia or bipolar disorder. He said that, while the parasite doesn’t directly cause mental illness, he believes strongly that toxoplasma is a risk factor.

The work of Czech scientist Dr. Jaroslav Flegr takes it a step further. Dr. Flegr is an evolutionary biologist at Charles University in Prague. Flegr discovered that individuals chronically infected with the parasite develop subtle personality changes. The organism appears to tweak brain circuits, slow down reaction times, and cause individuals to take more risks.

“He postulates that this is due to the fact that they don’t actually have the right conception of risk, of what its like, say, to cross the street when a car is coming against the light,” said Dr. Yolken.

But why would a parasite steer you into oncoming traffic, potentially killing you?

“It wants to survive and it’s very good at it,” commented Dr. Conrad.

Dr Conrad’s team studies the parasite in wild and domestic animals. In her Davis lab they grow the parasite in cultures and then cryogenically freeze them for future research.

Dr. Conrad said that since the parasite ultimately needs to get back into a cat to sexually reproduce, a number of studies — including one very good one by Stanford researchers — show how it performs a pretty nifty trick: If mice are infected with toxoplasma Gondi, Conrad said, the parasite goes to their brain and it alters their behavior.

Instead of running away from cats, mice will flock to cat urine. Here you find cats. The cat then eats the mouse, and the parasite gets back into the cat.

“That’s fatal attraction for a mouse.” said Dr. Conrad.

And while we’re not mice, once upon a time we were potential prey for bigger cats, said Dr. Flegr. That might explain why the parasite slows us down. It wants to get back into a bigger cat.

Not only that, but a small study done by Flegr on students found, when infected with toxoplasma, the male students preferred the scent of cat urine.

Dr. Montoya cautions while there is no hard evidence linking parasite to mind control in humans, he said that it’s worth studying. If you can prevent an infection, he said, it’s better than trying to treat the illness after the fact.

“The more we know about the potential consequences of this parasite, in the brains of humans, the more we will know where to act and how to prevent those unwanted consequences,” said Dr. Montoya.

But in the meantime, as a precaution, should we get rid of cats? For that answer, we turned to the experts and every person with whom we spoke was emphatic:

“Oh please no,” said Dr. Yolken, who owns cats.

“Absolutely not,” said Dr. Montoya, who has studied and done research on toxoplasma for 20 years.

“Of course not,” said Dr. Flegr who added cats really benefit our health.

“Everyone in our lab has cats. I have three cats,” said Dr. Conrad.

There are steps you can take to protect your cat. Cats get infected by eating infected wildlife, such as birds or rodents.

If you can, keep your cat indoors. Dr. Conrad said they will live longer, be healthier and then stay away from infected creatures.

If your cat needs to go outdoors, make sure they’re always well-fed so that they don’t hunt birds and mice for food. Also, make sure to bring them to the vet for regular checkups.

You can also put a bell on their collar to scare away their prey.

There are steps you can take to protect yourself. Wash all fruits and vegetables very carefully. If you camp, drink bottled water. Don’t drink water from streams or rivers. And since the parasite can be found in warm blooded mammals, cook your meat and game very thoroughly.

(Copyright 2012 by CBS San Francisco. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)

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