PHOENIX (3TV/CBS 5) - A common parasite found in cat intestines may take away the natural fear of dangerous behavior from some animals -- and humans. That's according to some past and ongoing scientific studies.

The most widely accepted of those studies show that mice that are infected with Toxoplasmosis lose their fear of the smell of cat urine. Cats are natural predators, so cat urine normally causes mice to run away.

Mice are infected by being exposed to cat feces. Humans become infected with Toxo the same way.

Other studies have shown a statistically higher number of infected humans die in traffic accidents and performing dangerous activities like riding motorcycles.

"It’s a very fascinating idea that you have this parasite that is manipulating your behavior in some ways that you don’t recognize," said Dr. Anita Koshy, who is an associate professor of neurology at the University of Arizona. She also runs the Koshy Lab, which studies Toxoplasmosis.

Koshy is interested in how Toxo can live in the human brain for decades without interfering with brain function. She believes that this parasite may some day help pave the way for treatments for other brain disorders like Alzheimers and MS.

But Koshy is skeptical that Toxo changes the behavior of humans, much less taking away their fear of daredevil activities.

"It's not so crazy to make this jump, especially in rodents," she said. "In a rat you can exactly control X, Y and Z. In a human, OK, well you’re infected with Toxo, but you’re probably also infected with a bunch of other things. And maybe it’s those other things or maybe it’s the exposure you had to whatever."

But something makes some people daredevils and others scared of heights and speed.

"I can’t explain why it’s not scary for me. It just seems like a normal thing to enjoy," said George Hargis who is a wingsuit pilot.

[WATCH: The world of daredevil sports]

"It means I pilot a small version of an aircraft made out of fabric. It flies much like an aircraft does," said Hargis.

She says she had a cat when she was a child and has no idea if that made her any braver, but she doesn't mind if it did.

"If I got it, that’s awesome! It benefits me now," said Hargis.

Morgan Loew's hard-hitting investigations can be seen weekdays on CBS 5 News at 6:30 p.m. and 10 p.m.

Copyright 2019 KPHO/KTVK (KPHO Broadcasting Corporation). All rights reserved.

Recommended for you