Targeting Common Parasite Could Help Treat Certain Mental Disorders


Abnormal immune reactions and related inflammation have been implicated in the etiology of mania (and bipolar, in general) and may contribute to the hallmark mood fluctuations of the disorder.8 A study published in January in Brain, Behavior, and Immunity discovered that people who tested positive for antibodies to T. gondii were twice as likely to have generalized anxiety disorder (GAD), and those with the highest level of antibodies had more than three times the odds of having GAD.9

It would seem logical to consider treating the toxoplasmosis in these cases, but more trials will be necessary before that becomes an option, and a viable medication will need to be developed.

“If we are correct that T. gondii plays a role in the causation of some cases of schizophrenia —and this is not yet proven — then it would be worth trying to treat the parasite and also to prevent the disease,” psychiatrist and researcher Fuller Torrey, MD, of the Stanley Medical Research Institute in Bethesda, Md., told Psychiatry Advisor. “The latter might be accomplished most easily by limiting exposure of children to cats, and in the long-term by developing a vaccine.”

The treatment part is trickier, since there are not yet viable pharmaceutical options for the latent stage of toxoplasmosis. “Most of the drugs which are effective against T. gondii only treat the active stage of the disease, not the chronic stage with brain cysts,” Torrey noted. “We are currently trying to develop effective drugs for the cyst stage.”

One study did find that adding artemether, an antimalarial medication, to treatment of first-episode patients with schizophrenia resulted in a decrease in negative symptoms on the Positive and Negative Syndrome Scale (PANSS), as compared to patients who were given a placebo along with their antipsychotic medication.10 Research co-authored by Fond also found promising results that deserve further exploration: In vitro experiments revealed that certain commonly used antipsychotic medications had higher anti-toxoplasmic activities than others. 

These findings may offer clues as to why some patients respond better to certain treatments. “Toxoplasmic status may be seen as a biomarker that may orientate the choice of treatment toward a treatment with high antitoxoplasmic activity,” says Fond.

Tori Rodriguez, MA, LPC, is a psychotherapist and freelancer writer based in Atlanta.


  1. Centers for Disease Control and Prevention. Parasites – Toxoplasmosis: Epidemiology & Risk Factors. Retrieved March 2, 2015 from
  2. Fond G, et al. Comparative analysis of anti-toxoplasmic activity of antipsychotic drugs and valproate. European Archives of Psychiatry and Clinical Neuroscience; 2014;264(2):179-83.
  3. Centers for Disease Control and Prevention. Parasites – Toxoplasmosis FAQs. Retrieved March 2, 2015 from
  4. Centers for Disease Control and Prevention. Parasites – Toxoplasmosis Treatment. Retrieved March 2, 2015 from
  5. Arias I, et al. Infectious agents associated with schizophrenia: a meta-analysis. Schizophrenia Research; 2012;136(1-3):128-36.
  6. Smith G. Estimating the population attributable fraction for schizophrenia when Toxoplasma gondii is assumed absent in human populations. Preventive Veterinary Medicine; 2014; 117(3-4):425-35. Dickerson F, et al. Antibodies to Toxoplasma gondii in individuals with mania. Bipolar Disorders. 2014; 16(2):129-36.
  7. Dickerson F, et al. A Combined Marker of Inflammation in Individuals with Mania. PLoS One; 2013; 8(9): e73520.
  8. Markovitz AA, et al. Toxoplasma gondii and anxiety disorders in a community-based sample. Brain, Behavior, and Immunity. 2015; 43:192-7.
  9. Wang H, et al. The effect of artemether on psychotic symptoms and cognitive impairment in first-episode, antipsychotic drug-naive persons with schizophrenia seropositive to Toxoplasma gondii. Journal of Psychiatric Research; 2014; 53:119-24.