Blaming Cats for Human Aggression

Is a cat to blame for this man's rage?
We doubt it.
Photo by dundanim via Adobe Stock.

If you have been tuned in closely to the news this week, you may have come across a headline like one of these:

• Blame Your Road Rage on That Cat Parasite, Says New Study (Newsweek)
• Explosive Road Rage Like–Anger Linked to Parasite Spread by Cats (Biospace)
• Common Cat Parasite Linked to Angry Outbursts in Humans (CBS News)
• Road Rage Could Be Linked to Cat Parasite (Irish Examiner)

Those were the reasonable—and reasonably accurate—ones. But then came these:

• Cats may be responsible for sudden outbursts of anger in humans (Fox 26)
• Cats Might Be the Reason Some People Are So Terrible (New York Magazine)

If we simply believe the headlines above, we can conclude that cats are making humans angry and “terrible,” right? The latest study says so, right?

Um, no.

Reality check: What the study actually said

There are many things I cannot abide, and one of them is an inaccurate, deceptive headline written specifically to draw attention to what may or may not be an accurate article. That’s why we tracked down the actual study and read it for ourselves. It’s titled "Toxoplasma gondii Infection: Relationship with Aggression in Psychiatric Subjects.”

The research included 358 participants. They were all physically healthy and were all evaluated for aggression, anxiety, depression, substance abuse, and something called intermittent explosive disorder (IED). Of the participants, 110 were healthy “controls” (had no psychiatric or personality disorder), 138 were diagnosed with some sort of disorder other than IED, and 110 were diagnosed with IED (characterized by “recurrent, problematic, impulsive, aggressive behavior,” [p. 337]).

The study next tested to see which subjects were infected with the Toxoplasma gondii parasite. Those who tested positive for the parasite were more likely to have high aggression and impulsivity scores and were more likely to have IED. Presence of T. gondii was also associated with depression, anxiety, and borderline and/or antisocial personality disorder, though not with self-aggression or self-harming.

What does this have to do with cats?

This photomicrograph shows
brain tissue infected with
spherical Toxoplasma gondii cysts.
CDC/Carey Callaway, 1966.
 Public domain via
CDC Public Health Image Library.

This is relevant to cats because, as some of the headlines helpfully pointed out, T. gondii is a “cat parasite.” Cats, wild and domestic, are the only known “definitive” or “ultimate” host for the parasite, which means that T. gondii reproduces only in cats. The parasite can infect many other animals though, including humans. In those intermediate hosts, the parasite forms cysts in different parts of the body, including muscles and the brain. Infected rodents can lose their fear of cats, making them more likely to be caught and eaten by a cat (and getting the parasite exactly where it wants to be: in its ultimate host, a cat).

According to the CDC, humans can get infected by

• eating undercooked meat
• consuming contaminated food or water or through contaminated soil (or a contaminated litter box)
• blood transfusion or organ transplantation
• from mother to fetus through the placenta

 Most healthy people who become infected do not show any symptoms, or they may have flu-like symptoms.  People whose immune systems are compromised  can have severe symptoms such as fever, nausea, headache, and seizures.

To reduce risk of infection, the CDC recommends

• cooking meats to safe temperatures
• thoroughly washing cutting boards, utensils, etc., that have come into contact with raw meats
• washing or peeling fruits and vegetables before eating
• wearing gloves when gardening, and washing hands when you’re done
• keeping outdoor sandboxes covered
• cleaning your cat’s litterbox daily (the parasite only becomes infectious 1–5 days after it is shed), and washing hands when you’re done

 By the way, if your cats are indoors-only and aren’t eating potentially infected rodents, their most likely source of infection is raw or undercooked meats (according to the American Veterinary Medical Association), so don’t feed them those things, and you’ll be further reducing your chance of infection.

What now?

First rule: Don’t panic.

Yes, a relatively small study linked T. gondii parasitic infection to increased aggression in humans, and yes, cats are the ultimate host for that parasite. That could sound scary for cat owners.

Use common sense to prevent
infection. If you're pregnant
or immunosuppressed, let
someone else change the litter box.
CDC/James Gethany, 2005.
Public domain via
  CDC Public Health Image Library. 

But think for a minute: How many cat owners do you know who are prone to exploding in rage at the least little thing? In our experience, “cat people” are some of the kindest humans you can possibly find. And by the way, She of Little Talent is living with a suppressed immune system following a lung transplant, and she lives happily and healthily with two indoor-only cats and without any overwhelming fear of contracting toxoplasmosis from them (though she doesn’t change the litter box, and she is a total freak about washing her hands).

The study’s authors also write that “it is also possible that impulsively aggressive individuals engage in behaviors that increase their own risk of infection with T. gondii” (p. 339). So the parasite-aggression connection could be a chicken-and-egg situation. Which comes first?

Even if toxoplasmosis is definitively shown to contribute to human aggression, you can protect yourself by using common sense and doing things you should be doing anyway: cook your meat, wash your fruits and vegetables, wash your hands.

One thing we can say definitively right now: No, cats are not the reason some people are so terrible.

Sources

American Veterinary Medical Association. Toxoplasmosis. https://www.avma.org/public/PetCare/Pages/Toxoplasmosis.aspx

Berdoy, Webster, & Macdonald. (2000). Fatal Attraction in Rats Infected with Toxoplasma gondii. Proc Biol Sci, 267(1452), 1591–1594. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1690701/

Centers for Disease Control and Prevention. (2013). Toxoplasmosis Frequently Asked Questions. http://www.cdc.gov/parasites/toxoplasmosis/gen_info/faqs.html

Coccaro et al. (2016). Toxoplasma gondii Infection: Relationship with Aggression in Psychiatric Subjects. Journal of Clinical Psychiatry, 77(3), 334–341. http://www.psychiatrist.com/jcp/article/Pages/2016/v77n03/v77n0313.aspx

Mayo Clinic. (2014). Diseases and Conditions: Toxoplasmosis. http://www.mayoclinic.org/diseases-conditions/toxoplasmosis/basics/causes/CON-20025859