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Why a Cat in the House May Cause Depression and Suicide

Tim Boyer's picture

Suicide accounts for approximately one death every 14 minutes. In 2009, there were 36,909 reported suicide deaths in the U.S. A primary risk factor of suicide includes repeated non-fatal attempts to commit suicide. Other risk factors or potential signs of impeding suicide such as changes in behavior, increased use of alcohol, or a recent death in the family offer little warning that someone may be depressed and considering to commit suicide. While an estimated 90% of all suicides are attributed to a diagnosed psychiatric disorder, researchers recently report that some cases of suicide may be linked to a common parasite found in cats.

In the August issue of the Journal of Clinical Psychology, researchers explain that some cases of suicide could be due to Toxoplasma gondii infection—an intracellular parasite hosted by cats that is passed onto humans. According to the researchers, Toxoplasma gondii may be carried by as much as 10% to 20% of the population.

Toxoplasma gondii is a single-celled parasitic organism that reproduces only in cats—both wild and domestic—and therefore is a carrier host for human infection.

According to the CDC, toxoplasmosis is considered to be a leading cause of death attributed to foodborne illness in the United States. While a large portion of the population carries the parasite, the majority are symptomless due to the protective abilities of a healthy immune system. In immunocompromised or people with a weakened immune system due to some medications or illness, the parasite can forms cysts that can adversely affect your muscles, your heart—and even your brain.

Infection in humans is typically due to:

• Coming into contact with cat feces that contain the parasite
• Eating contaminated food or drinking contaminated water
• Eating unwashed fruits and vegetables
• Using contaminated knives, cutting boards or other utensils
• Receiving an infected organ during transplantation surgery or transfused blood

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While depression is often attributed to low or significantly decreased levels of an important brain chemical called “serotonin,” previous research has led investigators to consider that the low levels of serotonin may be a symptom rather than a cause of depression. One hypothesis is that parasitic organisms that can get to the brain may cause inflammation that over time produces harmful metabolites that damage brain cells.

“Previous research has found signs of inflammation in the brains of suicide victims and people battling depression, and there also are previous reports linking Toxoplasma gondii to suicide attempts,” says Lena Brundin a researcher at Michigan State University and co-author of the study. “In our study we found that if you are positive for the parasite, you are seven times more likely to attempt suicide.”

In the study, 54 participants who had previously attempted suicide and 30 non-suicidal participants were given a version of a Suicide Assessment Scale questionnaire as well as the Montgomery Asberg Depression Rating Scale exam. The tests reportedly assess the level of a person’s depression and are predictive of the risk a person is for committing suicide.

What the researchers found was a positive association between testing positive for Toxoplasma gondii infection and scoring high on the suicide assessment tests.

The researchers believe that their results indicate that detection of Toxoplasma gondii infection may be a candidate marker/ risk factor toward identifying potential suicides before they happen and thereby provide opportunity for timely and successful intervention.

For more information about the study and its results, Michigan State University offers a free online copy of the study.

Image Source: Courtesy of MorgueFile

Reference: “Toxoplasma gondii Immunoglobulin G Antibodies and Nonfatal Suicidal Self-Directed Violence” Journal of Clinical Psychiatry 73(8), pp. 1069-1076, (Aug. 2012); Yuanfen Zhang, MD, PhD et al.



I have to say this is mostly B.S. I have lived with cats all of my life and I have not attempted to commit suicide. Depression is pretty common whether you have cats or not. I think I would be more depressed if I didn't have my cats. They are my little healers, my comfort at home.... my babies <3
I agree with you! Cats are great little therapists! :-)
I'm guessing that both the author of the article and the study are both desperately trying to justify their dislike for cats. People who have animal companions, both cats and dogs, tend to live longer and happier lives than those who do not. A cat's purr both lowers blood pressure and helps to heal bones. Cat owners have a lower risk of heart attack and stroke than non cat owners. Show some balance in your reporting, please.
Noooo! It's not about a dislike for cats at all. It's just a highlight that Toxoplasma gondii infection from cats could cause mental health issues. The bottom line should be to take care cleaning litter boxes. (I love my 9 cats by the way - yes 9 rescues!!!)
I have six cats. I am healthy and happy and so are my cats, two dogs and two rabbits. I feel depressed and low and sad when I have to be around people and all their "crap!" I say, if you want a happy, purposeful life and feel good about yourself everyday, adopt or rescue a homeless animal. The love you will experience will be more true and abundant from a beautiful animal than any person could ever bring into your life. The sad part however, is their little lives are so short, where as you have to put up with back stabbing, mean and revengeful people for far to many years. Keep your pets litter and feeding areas clean, keep your house clean, use a good air purifier or just open windows and it's just good common sense to be a diligent hand washer, just use soap and water and stay away from all those hand sanitizer. You wouldn't swallow antibiotics every hour, why kill eveything on your hand, you need the good bacteria. Follow these simple rules and living with pets will be happy, healthy and enjoyable. Eat clean, wholesome fresh food and feed your pet the highest quality diet possible and I promise you, you will not have shedding problems or high vet bills. I prepare my dog and cats food myself and they are in top notch shape. I think I am too busy being the best pet mom I can be and enjoying all the walks and fresh air with my dogs, and feeling all the love they have for my presence in their lives to have to much time to feel "depressed or suicidal" Please, science people, find something more important to spend valuable research money on. I don't think I've heard about the cure for cancer yet.......
As a mother of a struggling depressed daughter, I think it is a useful article and does not tell anyone to get rid of their cats. As it clearly states, not everyone will have symptoms, or indeed the parasite.