Study: Cats and Self-Directed Violence

There's more on Toxoplasmosis, the oppressively subtle brain parasite that 20% of us have. An association with increased suicidal behavior played out strongly in both women and men.

MAINscaryCAT.jpgI, for one, welcome our new feline overlords. [moyan_brenn/Flickr]

PROBLEM: Toxoplasmosis gondii, the parasite that uses cats as a host and is easily transmitted to humans (about 1 in 5 people in the United States have it, primarily via cat feces), is associated with a series of personality and behavioral changes. We become more "expedient, suspicious, jealous, and dogmatic." Those infected are three times more likely to die in car accidents, and more likely to develop schizophrenia. It even appears to alter our sexual attractiveness. Last month there was a massive study in Denmark that noted an association between Toxoplasmosis and suicidality in women. But the effects of toxo notoriously vary with the gender of the host.

METHODOLOGY: Fifty-four patients of both sexes in a Swedish hospital who had histories of attempting suicide were assessed, along with 30 control subjects, using a standardized self report for a history of self-directed violence and current suicidality (SUAS-S) and evaluated by psychiatrists. Blood tests determined their history of exposure to Toxoplasmosis. They also tested for commonly associated infections.

RESULTS: Testing positive for exposure to Toxoplasmosis (as well as the degree of one's immune response to it) correlated strongly with suicide attempts. 

CONCLUSION: Both men and women who tested positive for immune responses to toxo were seven times more likely to have a history of "nonfatal suicidal self-directed violence."

IMPLICATION: Clearly identifying Toxoplasmosis as a risk factor for suicide may be of benefit in risk stratification and suicide prevention. This study not only notes the association in both genders, but also found a much higher odds ratio than previous studies. Of course this correlation doesn't mean the relationship is causal. And by no means do you need to live with cats in order to contract toxo. It increases your risk of exposure, but there are ways that even high-risk immune-compromised people can live safely with cats.

How toxo affects us as a "mind-controlling parasite," and what we can and should do about it, warrants continued study. If this infection that we previously thought to be so benign can have such drastic effects on our behavior, how many other occult infectious processes go into shaping who we are? Nature vs. nurture vs. parasites. There's more discussion on the effects of Toxoplasmosis in our magazine feature from earlier this year. Also, digestible CDC info is here

Of course, cats bring us not only tragic brian parasites but also companionship and lolz. There's no way that's all part of their master plan! To be fair, here's a tumblr of kittens doing classic album covers, Laser Cats, and an official response statement "From the desk of: cats." 

SOURCE: The full study, out of Michigan State University, "Toxoplasma gondii Immunoglobulin G Antibodies and Non-Fatal Suicidal Self-Directed Violence," is published in forthcoming issue of The Journal of Clinical Psychiatry

Presented by

James Hamblin, MD, is a senior editor at The Atlantic. He writes the health column for the monthly magazine and hosts the video series If Our Bodies Could Talk.

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