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Cat parasite makes people psychotic


(NaturalNews) A new study, conducted by researchers from the Centre for Evolutionary and Functional Ecology in Montpellier, France, and published in the journal Current Biology, adds to the evidence that a parasite transmitted by domestic cats may cause psychiatric illness and instability in human beings.

The parasite in question, Toxoplasma gondii, has a complex life cycle. The organism can only reproduce if it infects the body of a feline, such as a house cat or leopard. There is no direct route of transmission for T. gondii from one feline to another, however. Instead, the parasite is shed in feline feces, from where it infects other animals. This infection is known as toxoplasmosis.

Long evolutionary history with primates

To date, research has focused on the parasite's infection of rodents. Scientists have conclusively shown that toxoplasmosis causes rodents to lose their fear of cats. This makes them more likely to be eaten, thus moving the parasite to a new feline host, where it can reproduce.

The new study shows for the first time that toxoplasmosis can also change the behavior of chimpanzees, our closest genetic relatives. Researchers exposed both toxoplasmosis-infected and non-infected captive chimpanzees to the urine of various big cats. They found that infected chimpanzees were three times more likely to investigate leopard urine, which chimpanzees normally find repulsive.

"It has been shown ... that T. gondii can induce behavioural change in parasitized rodents, making them more attracted to cat urine, thus benefiting parasite transmission," lead author Clemence Poirotte said.

"For the first time, we've shown that such parasite manipulation occurs in a primate, in a very specific way. We found that in our closest relative, the chimpanzee, Toxoplasma-infected animals lost their innate aversion towards leopard urine, their only natural predator."

Notably, infected chimpanzees did not become any more likely to approach the urine of lions or tigers. This suggests that T. gondii has co-evolved with chimpanzees over enough time to cause precise changes in their brain function that make them more likely to be eaten by leopards.

This lends support to the hypothesis that T. gondii may also cause targeted behavior changes in humans – rather than, for example, accidental changes that are simply side effects of the changes it causes to rodents.

"Our study rather supports the hypothesis that manipulative abilities of T. gondii have evolved in the human lineage when our ancestors were still under feline predation," Poirotte said. "Behavioural modifications in humans could thus be an ancestral legacy of our evolutionary past."

Forms cysts in human brain

The findings are being interpreted as support for an increasingly compelling hypothesis that toxoplasmosis may cause psychiatric disturbances in human beings. Several studies have shown that people with toxoplasmosis have slower reaction times, are more likely to take risks, and have higher rates of self-harming, suicide and even schizophrenia.

T. gondii is known to form cysts in the amygdala of the human brain, a region involved in regulating fear.

"Latent toxoplasmosis was commonly assumed to be asymptomatic in humans, except in pregnant women," Poirotte said. "Recent studies have shown that it could represent a risk factor for some mental disease such as schizophrenia, but more studies are needed to understand all the impacts on human health."

Toxoplasmosis infection is incredibly widespread among humans, with an estimated 60 million people infected in the United States alone. Infection occurs after exposure to cat litter, either through pet cats or contaminated food.

Toxoplasmosis is highly dangerous for pregnant women or people with compromised immune systems. The U.S. Centers for Disease Control and Prevention (CDC) consider it one of the leading causes of death from foodborne illness, and have named it a "neglected parasitic infection," targeted for special attention.

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