On Cats and Death


A few years ago, five kids at my old high school committed suicide in the span of less than a year. The train tracks by the school helped them out, but what really drove this sudden surge of suicide is a mystery. When I heard about this suicide epidemic, my first thought was that it seemed almost infectious. But come on, it’s not like there’s something in the water, right?

Now this is a giant leap, but two new studies just came out confirming previous findings that a common parasite transmitted by cats correlates with suicide risk. While I doubt this is the grand answer explaining why people kill themselves, I’d say exploring the connection between this parasite and suicide is certainly an idea worth considering.

Toxoplasma gondii (T. gondii) is a fairly common parasite that reproduces primarily in cats, but can also infect humans. In humans it initially causes a flu-like illness, but after the immune system fights off the parasite it retreats to the brain where it hides out indefinitely. Here it is thought to be pretty much harmless, lying dormant in 10-20 percent of people in the U.S. and about one third of the world’s population.

That might be an outdated mode of thinking, though, since loads of new research continues to find that latent T. gondii infection may not be as benign as we once assumed it to be. Two studies published by scientists in the U.S, who collaborated with researchers in Sweden and Denmark, found that people infected with T. gondii had a greater risk of attempting suicide.

The Swedish study looked at 54 patients admitted to a Swedish hospital after a suicide attempt, along with 30 control individuals from the same city. They found that people infected with T. gondii were a whopping seven times more likely to have attempted suicide than those who tested negative for the parasite.

In the Danish study, they looked not at correlation with past suicide attempts, but sought to determine whether past T. gondii infection could help predict future suicide attempts. Thanks to the brilliant national registers in Denmark, they were able to track 45,788 women for more than 10 years. The women were initially recruited as an effort to screen newborns for T. gondii infection, so they measured T. gondii antibodies in the baby’s blood to determine whether or not the mother was infected. They found that women who were infected with T. gondii when they gave birth were 1.53 times more likely to attempt suicide in the future than uninfected women, and that having more antibodies towards T. gondii increased this risk (those with the higher levels of antibodies had 1.93 times the risk of future suicide attempts). Although very few women in this study actually committed suicide, they were still able to calculate that T. gondii infection was associated with 2.05 times the risk for a future suicide.

The researchers suspect that T. gondii infection may cause inflammation in the brain in some infected individuals, which could be related to certain changes in brain chemistry that have been observed in depressed and suicidal individuals. Previous studies have identified several mediators of the immune system present at elevated levels both in those who have attempted suicide and in those positive for T. gondii, suggesting a possible mechanism underlying this connection. At this point, though, it’s also possible that such changes in the immune system could predate and increase later susceptibility to both suicidality and T. gondii infection.

Despite my depressive tendencies and magnetic attraction to those far more depressed than me, suicide is still an entirely foreign realm. I don’t think it would be fair to add increased risk of suicide to my list of why dogs are better than cats, but a simple answer to what pushes some over that edge would be so nice to find.



Very informative article.

Very informative article. Thank you! My girlfriend has a cat with a multitude of problems (allergic to almost everything under the sun) and works in a vet office. She is just recently coming down with Flu like symptoms, so I am going to forward this to her. Toxoplasma gondii sounds like a nasty parasite.

I've been depressed before as well Cindy, when I was younger I thought about suicide a few times but ultimately decided against it because I knew it would completely tear my mothers world apart. Anytime you are feeling down remember that there would be a multitude of people that would miss you, and it would cause them a lot of pain if anything happened to you. I hope everything is going good since the publish date in Sept of 2012.


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