A Parasite Carried By Cats Could Increase Suicide Risk

A Parasite Carried By Cats Could Increase Suicide Risk
by Jon Hamilton - NPR
July 2, 2012

What's the link between cats and madness?

There's fresh evidence that cats can be a threat to your mental health.

To be fair, it's not kitties themselves that are the problem, but a parasite they carry called Toxoplasma gondii.

A study of more than 45,000 Danish women found that those infected with this feline parasite were 1.5 times more likely to attempt suicide than women who weren't infected.

That's not a huge increase, but it's probably too big to have been caused by chance, says Teodor Postolache, a University of Maryland psychiatrist and senior author of the paper, which was published in the Archives of General Psychiatry.

Still, the absolute risk of suicide remains very small. Fewer than 1,000 of the women attempted any sort of self-directed violence during the 30-year study span. And just seven committed suicide.

But this isn't the first time T. gondii infection, or toxoplasmosis, has been associated with behavioral changes in people, Postolache says. Previous studies have shown links to schizophrenia, bipolar disorder, and even the chance that a person will get in an automobile accident.

The T. gondii parasite lives in the intestines of cats. Cat owners can become infected when they change a litter box, Postolache says. But he says people are more likely to be infected when they eat vegetables or meat that are raw or undercooked.

"People should not give their cats away" because of this study, Postolache says.

Scientists still aren't sure how the parasite affects a person's brain, he says. But in rodents, it causes cysts to form in areas of the brain involved in behavior.

A study of rats also found that infection caused them to lose their fear of cats and become attracted to the odor of cat urine. That behavioral change would increase the chance that a rat would be eaten by a cat — allowing the parasite to get into the cat's intestine, which is the only place it can reproduce sexually.

The parasite doesn't benefit much from infecting a human, since cats don't eat people very often. So humans are probably just "collateral damage" from the parasites' effort to infect smaller animals, says Robert Yolken, an infectious disease expert at Johns Hopkins University.

Yolken says he owns two cats and that "the benefits outweigh the risks."