Toxoplasmosis–Schizophrenia Research

(Last updated September 2018)

Welcome to the Toxoplasmosis–Schizophrenia Research section. This site is maintained by the Stanley Medical Research Institute (SMRI) and the Stanley Division of Developmental Neurovirology for researchers and others interested in the possible etiological relationship between Toxoplasma gondii (and related organisms) and schizophrenia (and related psychoses). The purpose of the webpage is to make information on this line of research, including background data and current research, easily available.

This section will be updated periodically. Comments, suggestions, additions, and corrections are welcomed. They can be sent to either E. Fuller Torrey, MD, or Robert H. Yolken, MD.

Related sites:
ToxoDB: provides detailed information on the genome of Toxoplasma gondii
Schizophrenia Research Forum: a useful online forum to keep updated on schizophrenia research


SMRI has undertaken extensive research on infectious agents as one of the possible causes of schizophrenia. Among the infectious agents that appear most promising is Toxoplasma gondii, a protozoan parasite that causes toxoplasmosis and is carried by cats and other felines. Until recent years, toxoplasmosis was thought to be a problem only for pregnant women who, if they became infected with T. gondii during their pregnancy, risked having the organism cause damage to the growing fetus. This is why pregnant women are advised to not change the litter in the cat litter box. Infection with T. gondii in other adults and children was thought to be either asymptomatic or to cause an influenza-like or mononucleosis-like syndrome. It now seems possible that T. gondii may be associated with some cases of schizophrenia and perhaps other psychiatric syndromes.

Schizophrenia is a brain disease that begins in young adults, typically between the ages of 16 and 30, and is characterized by some combination of auditory hallucinations (hearing voices), delusions, flattened affect, disordered thought patterns, bizarre behavior, and social withdrawal. Schizophrenia affects approximately 1 percent of the adult population and in most cases is a lifelong disease with remissions and exacerbations. It is also a very expensive disease. A 2013 study estimated the cost of schizophrenia in the United States at more than $155.7 billion a year.

For additional information on schizophrenia, see Torrey EF, Surviving Schizophrenia, 7th edition (New York, HarperCollins, 2019).


Summary: What links T. gondii to schizophrenia and related psychoses?

  • More than 100 studies have reported increased antibody levels to T. gondii in individuals with schizophrenia and related psychoses.
  • Four out of six studies have reported that individuals with schizophrenia, compared to controls, have had more contact with cats during childhood.
  • T. gondii has been shown to make dopamine, thought to be elevated in individuals with schizophrenia.
  • Epidemiologically there are many similarities between schizophrenia and toxoplasmosis.
  • Some antipsychotics have been shown to suppress T. gondii.
  • A study in China reported that having antibodies to T. gondii at the time students entered college made it significantly more likely that the student would be diagnosed with psychosis during the next four years.

Topics of Interest

I. All About Cats

  • Origin, domestication and early history
  • Modern history
  • Distribution and number of cats
  • Cat feces and T. gondii oocyst distribution

II. Transmission of T. gondii

  • Ingestion of tissue cysts
  • Ingestion or inhalation of oocysts
  • Vertical transmission from infected mother to offspring
  • Sexual transmission of T. gondii
  • Timing of infection by T. gondii
  • Do people with close cat contact have a greater chance of being infected with T. gondii?
  • Do children with close cat contact have a greater chance of developing schizophrenia?

III. Epidemiological Similarities and Differences Between Toxoplasmosis and Schizophrenia

  • Familial and genetic aspects
  • Age of onset
  • Males get sick at a younger age than females
  • Socioeconomic status and household crowding
  • Seasonal variation
  • Association with stillbirths
  • Geographic low-prevalence toxoplasmosis regions
  • Historical trends
  • Urban-rural differences
  • Geographic high-prevalence toxoplasmosis regions
  • Historical trends

IV. Effects of T. gondii on Behavior and Psychiatric Symptoms

  • Early Research
  • Behavioral manipulation by T. gondii  in animals
  • Effects of T. gondii  on personality traits of humans
  • Effects of T. gondii  on cognition in humans
  • Effects of T. gondii  on reaction time and vehicular accidents
  • Psychiatric manifestations of congenital T. gondii  infections
  • Psychiatric manifestations of adult T. gondii  infections
  • The effects of different strains of T. gondii

V. Studies of T. gondii Antibodies in Schizophrenia

  • Studies of antibodies in individuals who have schizophrenia
  • Studies of antibodies in individuals prior to the onset of schizophrenia
  • Studies of T. gondii antibodies in the mothers of children who are later diagnosed with schizophrenia
  • Do antibodies to T. gondii  remain detectable over many years?

VI. Neurotransmitters and T. gondii

  • Origin of interest in dopamine and T. gondii
  • Toxoplasma gondii  has the ability to make dopamine
  • Effects of changing levels of dopamine on behavior induced by T. gondii  infection
  • Effects of T. gondii  infection on GABA
  • Strain differences in effects on neurotransmitters

VII. Neuropathology of  T. gondii

  • Neuropath studies of T. gondii  in schizophrenia
  • Other means of identifying T. gondii  in brain tissue
  • T. gondii and the intestine
  • T. gondii and the eye

VIII. Treatment Approaches to Toxoplasmosis and Schizophrenia

  • Background: Protozoa
  • In vitro studies
  • Trials of drugs known to be effective against T. gondii  on patients with schizophrenia

IX. Toxoplasmosis and Other Diseases

  • Bipolar Disorder
  • Obsessive-Compulsive Disorder
  • Depression and Anxiety Disorder
  • Suicidal Behavior
  • Substance Abuse
  • Intermittent Explosive Disorder
  • Multiple Sclerosis
  • Parkinson’s Disease
  • Migraines
  • Epilepsy
  • Alzheimer’s Disease
  • Brain Cancer
  • Obesity
  • Rheumatoid Arthritis