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Toxoplasmosis and Toxic Media—Commentary

11/04/16 John H. Greist, MD, University of Wisconsin School of Medicine and Public Health|Madison Institute of Medicine;

A recent study was cautiously titled “Toxoplasma gondii infection: relationship with aggression in psychiatric subjects” (reference 1). It found toxoplasmosis, caused by a protozoan parasite, in 22% of individuals with intermittent explosive disorder (IED), in 17% of those with another psychiatric disorder but without IED, and in 9% of people with no psychiatric disorder. 

Although toxoplasmosis is present in about one-third of the world’s human population, few experience any symptoms of illness. Toxoplasmosis is acquired by eating undercooked contaminated meat, drinking contaminated water, or swallowing the parasite through contact with cat feces containing the parasite. 

Because cats can transmit the illness, the study has elicited numerous sensational news articles, among them:

The Telegraph: Owning a cat can lead to mental health problems, study warns.  If you're prone to sudden bursts of anger, it could be your cat's fault (reference 2)

Newser: Parasite found in cat poop linked to rage disorder; Toxoplasmosis has been linked to host of neurological disorders (reference 3)

Based on evidence from this study, should doctors test for toxoplasmosis in everyone with IED and treat those who test positive? We are a long way from knowing what effect, if any, toxoplasmosis has on individuals with IED. While 22% of those with IED in this study tested positive for toxoplasmosis, 78% with IED did not. Whether treatment of toxoplasmosis would have any beneficial effect on IED sufferers with toxoplasmosis is unknown, but we do know toxoplasmosis treatments can cause adverse side effects. For balanced and authoritative information on toxoplasmosis, please see the Centers for Disease Control and Prevention website.

Because physicians understand there is so much they do not understand, medicine’s conservative side is strongly expressed in one of its cardinal rules: First, do no harm. There is a long record of seemingly certain medical beliefs that were later found to be wrong or even dangerous (reference 4). The path to medical certainty is long and arduous and requires rigorous replication in randomized controlled trials.  The authors of this report conscientiously acknowledged that theirs was a single study with “a cross-sectional design," and "no causal, or directional, conclusions can be made from these analyses.”

A large part of the news industry has different ethical standards and applied practices falling short of All the news that’s fit to print.  This part of the industry trades on human curiosity, suggestibility and revulsion and is comfortable with an extension of first amendment protection of free speech that tips the balance in the direction of let the reader beware. 

As Mark Twain observed: “If you don't read the newspaper, you're uninformed. If you read the newspaper, you're mis-informed.”


  1. Coccaro EF, Lee R, Groer MW, et al. Toxoplasma gondii infection: Relationship with aggression in psychiatric subjects.  Journal of Clinical Psychiatry 77:334–341, 2016.
  2. Adam Boult.  The Telegraph.  March 30, 2016.
  3. Elizabeth Armstrong Moore.  Newser.  March 31, 2016.
  4. VK Prasad and AS Cifu. Ending Medical Reversals.  Johns Hopkins Press, 2015.

See Dr. Greist's discussion of Anxiety Disorders in The Manual.