Mice lose cat fear for good after infection

Mice may permanently shed a fear of felines when infected with a parasite. The effects linger long after the parasites disappear, a study shows.

The protozoan parasite Toxoplasma gondii can infect most mammals, including humans (SN: 1/26/13, p. 24). But the parasite can reproduce only in the feline gut, so cats need to eat animals infected with T. gondii to keep the parasite generations going.

Perhaps increasing the likelihood that it will wind up in the belly of a cat, the parasite makes infected rodents lose their innate aversion to cat urine, researchers discovered in 2000. The parasite strain was so potent that it killed the mice quickly, so researchers had no way of knowing whether the rodents’ loss of cat aversion could persist.

Researchers led by Michael Eisen at the University of California, Berkeley report September 18 in PLOS ONE that a loss of repulsion to cat urine lingered four months after infection with less-virulent T. gondii strains, even in mice that had cleared the parasites from their bodies. The researchers propose that a transient infection with the parasite permanently alters the way the rodents’ brains perceive predator threats.

Editor’s Note: This story was updated on September 25, 2013 to correct the length of time the lack of repulsion lasted in the researchers’ test.