Parasite Brainwashes Mice to Not Fear Cats

A mind-altering parasite causes mice to become permanently fearless around cats, according to a new PLoS ONE study that further suggests this creepy parasite could be present in many human brains.

The parasitic protozoan, Toxoplasma gondii, has a near foolproof life cycle. It infects mice, which are then eaten by hungry felines (mostly feral), which can then serve as a reservoir for the parasite, since it sexually reproduces in a cat's intestinal tract.

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But the parasite doesn't just sit in the gut. It can also go to the brain, where it may cause the individual to exhibit behavioral changes - such as overconfidence in mice.

"Even when the parasite is no longer in the brains of the animals, some kind of permanent long-term behavior change has occurred, even though we don't know what the actual mechanism is," UC Berkeley graduate student Wendy Ingram, who worked on the study, said in a press release.

Ingram and colleagues Michael Eisen and Ellen Robey tested mice by seeing whether they avoided bobcat urine, which is normal behavior, versus rabbit urine, to which mice don't react. The researchers found that the three most common strains of T. gondii make mice less fearful of cats for at least four months.

The effect likely is then permanent. (And one wonders how long such a mouse would be in the land of the living anyway, given how easy it would be for cats and other animals to catch them.)

It should be noted that the scientists used a genetically altered strain of T. gondii that cannot form cysts and so is unable to cause chronic infections in the brain. The team is now looking at how the mouse immune system attacks the parasite to see whether the host's response to the infection is the culprit.

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The take home message, though, is that if you have pets - especially cats– keep them indoors whenever possible. There are many reasons for doing this, but preventing them from getting a potentially brain-altering parasite is a pretty compelling one.

Also wash your hands after tidying up an indoor cat's litter-box. Another route of transmission is eating underdone pork, since pigs can also become infected with this parasite, so experts advise cooking pork to at least 160 degrees F.

Ingram said other studies have found that one-third of the world's human population has been infected by T. gondii and probably have dormant cysts in their brains.

She added that, when kept in check by the body's immune system, these cysts sometimes revive in immune-compromised people, leading to death. Some preliminary studies suggest that chronic infection may be linked to schizophrenia or suicidal behavior.

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We obviously haven't heard the last about this bizarre parasite. As Ingram said, "Toxoplasma gondii has done a stunning job of adapting to mammalian brains in order to enhance its transmission through a complicated life cycle."

Photo: Wendy Ingram

Thanks to the unstoppable power of the Internet phenomenon known as the cute pet viral video, even animals are getting their crack at the realm of global celebrity. Here are five famous pets who have landed TV appearances, corporate sponsorships, book contracts and even movie deals from their viral video success.

Henri le Chat Noir

Filmed in moody monochrome, the Henri le Chat Noir oeuvre features world-weary feline Henri, a melancholy and terribly serious little cat who reflects upon his world with resigned, existentialist despair. In French. With subtitles."The cardboard box, a comfort to most cats, was my pit of despair," Henri laments in the latest video. "And when I reached the top, it toppled from the weight of my own ennui." Henri le Chat Noir is the brainchild of William Braden, who created the first of the six videos as a student film project. In April, Ten Speed Press released Henri's first book, "Henri, le Chat Noir: The Existential Musings of an Angst-Filled Cat."

Giant George, The World's Biggest Dog

For several years, the Great Dane named Giant George held the official Guinness record for tallest dog on the planet -- 43 inches. That's measured at the shoulders, mind you. End-to-end, George is about 7 feet long and 250 pounds. For his appearance on the Oprah Winfrey show in 2010, George was given his own row of three seats. "Giant George: Life with the World's Biggest Dog," published in 2012 and written by owner Dave Nasser, earned surprisingly good reviews. Publisher's Weekly: "Startlingly honest and well-written, Giant George's story stands apart from the slew of other dog books on the shelves."

Chris P. Bacon

Born with malformed hind legs, the piglet now known as Chris P. Bacon (sound it out) was saved from euthanasia when Florida veterinarian Len Lucero took pity on the li'l fella. Using spare parts and kids' toys, Lucero built a harness/wheelchair for the piglet and the subsequent videos went viral. That led to a three-book deal with Hay House, publisher of inspirational and self-help books. The titles, to be penned by Dr. Lucero and co-writer Kristina Tracy, are part of Lucero's larger initiative to reach out to and inspire handicapped children. The first book hits shelves this fall.

Grumpy Cat

The stern but fuzzy Internet meme known as Grumpy Cat (real name Tardar Sauce) made her debut with a simple online pic in late 2012. She's since lent her disapproving visage to a million image macros and online gags. Due to her particularly cranky facial expression (caused by feline dwarfism), Grumpy Cat has become a genuine celebrity, with dozens of TV appearances, various Internet awards, an expanding line of merchandise and -- yes -- a book deal. She's got a movie in the works, too. Producer Todd Garner has optioned Grumpy Cat for a Garfield-style feature film adaptation. “You read all of the memes and the comments, and one is funnier than the next," Garner told Deadline Hollywood. "We think we can build a big family comedy around this character.”

Boo, The World's Cutest Dog

"My name is Boo. I am a dog. Life is good." So reads the digital inscription on the Facebook page of Boo, probably the Internet's single most famous animal. Boo earned celebrity status way back in 2010 when a series of Facebook photos -- either adorably cute or deeply disturbing, depending on your point-of-view -- captured the attention of celebrities like Khloe Kardashian and Ke$ha. The Facebook page now has more than 7 million fans and last year Boo was appointed Official Pet Liason for Virgin America Airlines. Boo has endured his share of celebrity tribulations as well, including a Twitter death hoax and the scandalous disclosure that Boo's owner is … wait for it … a Facebook executive. Now a bonafide merchandising force, Boo has since issued several wall calendars, a line of plush toys, a children's ABC primer, and two hardback photo books: "Boo: The Life of the World's Cutest Dog" and last year's "Boo: Little Dog in the Big City."