The crazy cat lady (or man) syndrome is real, says Czech scientist Jaroslav Flegr.

The biology professor at Charles University in Prague believes a protozoan parasite found in cat feces can manipulate a person’s brain — leading to mood disorders, such as schizophrenia, traffic accidents and even suicides.

For the last 20 years, Flegr, an evolutionary biologist and parasitologist, has studied the effects of Toxoplasma gondii in humans. After noticing some strange patterns in his own behaviour — not perceiving danger in dangerous situations, which can be a hallmark of the manipulation — Flegr was tested to see if he was infected. He was.

Scientists have long-known that Toxoplasma gondii causes toxoplasmosis — a disease 60 million people unknowingly carry, according to estimates from the Centers for Disease Control and Prevention in the U.S.

Most people are unaware they are carriers, as those with healthy immune systems experience nothing more than mild flu-like systems when they first become infected. Toxoplasmosis can be dangerous for people with weakened immune systems, and pregnant women are often cautioned to avoid cleaning a cat’s litter box as extreme cases of toxoplasmosis can lead to developmental defects in the unborn child.

Flegr, 53, who has studied toxoplasmosis in people through a series of personality questionnaires, believes one-third of the world’s population is infected by Toxoplasma gondii.

In addition to cleaning a cat’s litter tray, a person can become infected by eating raw or undercooked meat of infected grazing animals, eating unwashed vegetables that have been grown in infected soil, drinking water that has been contaminated by cat feces and through blood transfusions and organ transplants from a Toxoplasma-infected person.

Through his studies, Flegr has discovered males and females with toxoplasmosis behave differently. While men with toxoplasmosis are more likely to act suspicious, infected women show warmth.

As well, infected men have higher levels of testosterone compared to uninfected subjects, while infected women have lower levels of testosterone compared to their uninfected counterparts.

Flegr estimates approximately 30 per cent of the population in the Czech Republic is infected. In Canada and the U.S., the rates are much lower.

“In nearly all European countries the frequency of toxoplasmosis is going down,” Flegr said. The drop can be attributed to the improved methods of how people cook and prepare meat, he said.

In his studies, Flegr references reports that link toxoplasmosis with schizophrenia. A 2003 study by Edwin Fuller Torrey, of Stanley Medical Research Institute, and Robert H. Yolken, of Johns Hopkins University Medical Center, mentions how humans infected by the parasite “can produce psychotic symptoms similar to those displayed by persons with schizophrenia.”

Flegr isn’t trying to scare people; rather he hopes people become aware of the manipulation factors of Toxoplasma gondii.

“Human behaviour is very variable. People differ because they have different genes and they have been influenced by different environmental factors,” he said. “Toxoplasmosis is only one of many environmental factors.”

He does warn that an infected person “should be more careful” when driving, as his studies have led him to believe there is a risk of fatal traffic accidents in Toxoplasma gondii-infected people, as they tend not to perceive danger and have impaired reaction times. Latent toxoplasmosis is to blame for one million traffic-related deaths, Flegr writes in a 2010 study.

“In nearly all European countries the frequency of toxoplasmosis is going down,” Flegr said. The drop can be attributed to the improved methods of how people cook and prepare meat, he said.

“In the present time a lot of people eat frozen or at least cooled meat, and Toxoplasma doesn’t like this.”

Flegr’s research references numerous studies on the effects of toxoplasmosis in rats, indicating that in infected rats it can change the rat’s fear of cats into an attraction to a cat’s odours.

“A Toxo-infected rat looks and acts, in general, happy and healthy and very much like an uninfected rat,” Joanne Webster, professor of parasite epidemiology at Imperial College London, who has studied the effects of Toxoplasma gondii in rats, wrote in an email.

“However, specific behaviours likely to enhance transmission to the cat definitive host are subtly altered/manipulated. They are more active, less neophobic (fearful of new things) and in particular have the ‘fatal feline attaction’ where they are actually attracted to the feline definitive hosts.”

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Webster, who finds Flegr’s studies “very complementary,” doesn’t think people should be alarmed by the findings.

“I don’t think people should be complacent about such a highly prevalent parasite in the (central nervous system) of humans. However, there is certainly no need for panic.

“The severe pathologies, such as schizophrenia, are likely to occur in a very rare and few set of people, as a result of complex gene-environmental interactions — aspects for which we need further research to understand fully.”