Parasite Makes Rats Crave Cat Pee

A parasite called Toxoplasma gondii has a unique mechanism to help it spread: "tricking" rats into delighting in the smell of its predator, cats. This is an important adaptation since this parasite can only sexually reproduce in the gut of cats, so the parasite needs to get the infected rats into the cats' gut. Yeah, the cat eats the rat, and the parasite lives happily ever after.

Normally rats have a strong aversion to the scent of cat urine, but infected rats completely lose their aversion to cat pee but retain all their other fears and phobias.

"Toxoplasma affects fear of cat odors with almost surgical precision," Vyas concluded. "A large number of other behaviors remain intact."

What happens is that Tomoplasma infection induces cysts to form in the brain, specifically in the amygdala. This region of the brain is involved in fear response, and the cysts disrupt that normal response. In fact, it goes even further--the rats are actually *attracted* to the cat urine. The team is now examining how the parasite can target just one behavior so specifically.

Below: Representative scatter plots depicting the location of a control rat (C) and an infected rat (D) during trial, with respect to bobcat and rabbit urine.
i-ad6aa09ed577a9f82cf2b9c12cbcc634-cat pee 1.bmp

Vyas et al. 2007. Behavioral changes induced by Toxoplasma infection of rodents are highly specific to aversion of cat odors. PNAS. Early Edition April 5th. (

For more on this, check out Carl Zimmer's post on The Loom.


More like this

...for rodents and men at least. A team of researchers at UC Berkeley have discovered that mice infected with the parasite Toxoplasma gondii lose their innate fear of cats, even months after the infection is cleared. In fact, infected mice were mildly attracted to the odor of cats. This side effect…
Reports are coming out this morning on a new study on one of the Loom's favorite organisms: Toxoplasma gondii, the single-celled parasite that lives in roughly half of all people on Earth and has the ability to alter the behavior of its host. I reported on the research last June in the New York…
Are brain parasites altering the personalities of three billion people? The question emerged a few years ago, and it shows no signs of going away. I first encountered this idea while working on my book Parasite Rex. I was investigating the remarkable ability parasites have to manipulate the…
The parasite Toxoplasma gondii is common in rats, but can only sexually reproduce inside the belly of a feline. The solution? Brainwash the rats into craving the scent of cat urine. Once infected by Toxoplasma gondii, rats who would normally have a phobia of cat urine actually seek it out,…


I wonder, there were some papers discussing the role of Toxoplasma gondii's role in human evolution as well. Perhaps the effect it has in human beings is not a direct efffect on it's own evolution,but rather a side effect on the selective process towards making it a more effective "brain sugeon" in rats?

Fox, do you know which papers discuss Toxo and humans? Sounds interesting.

Kurt: Hopefully those cat owners aren't *attracted* to the smell! :)

I think Carl Zimmer had a few posts here last year on different aspects of toxoplasma. There was one about a link with schizophrenia and another about possible cultural side-effects. Here's a post from The Loom that has some links to articles.

Shelley Batts:

this parasite can only reproduce in the gut of cats

Carl Zimmer:

It's only in cats that Toxoplasma can reproduce sexually. [...] But Toxoplasma can also reproduce like a clone, splitting in two, either in cats or outside them.

SB: Ahhh. Thanks for the clarification!

By brtkrbzhnv (not verified) on 05 Apr 2007 #permalink

My favorite Science News article from a few years ago was about this. No only is the subject fascinating, but I loved the ending of the article, in which the speculations of the Oxford researchers on the effect of an infection in humans were reported:

In people, a latent infection can flair up and cause mental decline. Now, the researchers speculate that low-grade infections may result in more subtle effects, such as odd behavior and IQ dips. They estimate the parasite infects 22 of the UK residents and 88 percent of the French.

To this day, I don't know whether the estimates were real or not, but I prefer to believe that it was a joke that got by the editors of Science News.

Fascinating! Cysts! I didn't know that T. Gondii had could turn into a cyst form. I must have missed that study abstract when I was recently reading about toxoplasma (maybe it was Toxo in my brain making me miss it! lol)

And yes apparently a large majority of the population have antibody titers towards toxoplasma, and a lot of people could be infected to a certain degree.

It is believed toxoplasma can alter dopaminergic functionality, amongst other things. There are a few studies attempting to correlate personality changes to toxoplasma.