Can Toxoplasmosis Lead to Schizophrenia?

The famous drawing here is by Louis Wain, an English cat artist who in his later years developed schizophrenia, which some think may have been due to toxoplasmosis caused by his prolonged exposure to cats. A recent study [1] from Walter Reed Army Institute of Research and Johns Hopkins Childrens Center, suggests that Toxoplasmosis, an infection with the Toxoplasma gondii parasite, carried by cats and farm animals, may in fact, raise the risk of a person developing schizophrenia.

Published in the January issue of the American Journal of Psychiatry, the study finds that of 180 subjects diagnosed with schizophrenia, 7 percent had been infected with toxoplasma prior to their diagnosis, as compared with 5 percent among the 532 healthy recruits.

People exposed to toxoplasma had a 24 percent higher risk of developing schizophrenia. The difference, while seemingly small, is important, researchers say, because the ability to explain even a small portion of the 2 million cases of schizophrenia in the United States may offer clues to the disease and some possible treatments.

Antiparasitics for Mental Problems


The researchers are planning to study if aggressive treatment of toxoplasma infections with antiparasitic drugs in schizophrenic patients could halt the progression of the mental disorder. Toxoplasma gondii is a species of parasitic protozoa of the genus Toxoplasma. [2] The majority of toxoplasma infections happen early in life, following an exposure to the parasite in cat feces or undercooked beef or pork. Infections hardly ever cause symptoms, but the parasite stays in the body and can reactivate after lying dormant for years.

6 paintings of cats by Louis Wain

6 paintings of cats by Louis Wain with an increasing degree of abstractedness, attributed by some to his suffering from schizophrenia

An interesting sidenote is that T. gondii infections have the amazing ability to change the behavior of rats and mice, making them drawn to rather than fearful of the scent of cats. This effect is advantageous to the parasite, which will be able to sexually reproduce if its host is eaten by a cat.[7] Infections are quite precise in targeting, as they do not impact a rat’s other fears, for example fear of open spaces or of unfamiliar smelling food.

Correlations have also been found linking latent Toxoplasma infections and assorted characteristics like decreased novelty-seeking behavior, slower reactions, neurotic traits, and feelings of insecurity. [8] Could this behaviour altering ability have some role in the schizophrenia-triggering effect seen in the studies? If you want to read a fascinating book on this subject, pick up Carl Zimmers book Parasite Rex : Inside the Bizarre World of Nature’s Most Dangerous Creatures. Get ready for a gripping tale of genetic parasites, guinea worms, flukes, and T.gondii.

Other Infectious Agents

Ever since 1896, when Scientific American published an article under the heading “Is Insanity Due to a Microbe?, there has been interest in the link between infectious diseases and schizophrenia. Recent studies have found associations with schizophrenia and newborns exposure to such viruses as rubella virus [3], herpes simplex virus [4], and polio viruses [5].

The largest number of previous studies of this type have reported on the link between schizophrenia and the presence of toxoplasma antibodies. A recent meta-analysis cites 42 studies [6].

“Our findings reveal the strongest association weve seen yet between infection with this very common parasite and the subsequent development of schizophrenia,” says Robert Yolken, M. D., a neurovirologist at Hopkins Childrens who was among those conducting the analysis.

Although toxoplasma antibodies are evidence of past infection, this is the first study to show that infection with the parasite can precede the initial onset of symptoms and subsequent diagnosis with schizophrenia, Yolken says.

“Until now, the only thing we could say is that some people with schizophrenia also had been infected with toxoplasma at some point, but we couldnt tease out which came first. With our current study, we were able to show that infection came first.”

While most people infected with toxoplasma never develop schizophrenia, the parasite may be a trigger in those genetically predisposed to the disorder, a classic example of how genes and environment come together in the development of disease, Yolken says.


1 David W. Niebuhr, M.D., M.P.H., M.Sc., Amy M. Millikan, M.D., M.P.H., David N. Cowan, Ph.D., M.P.H., Robert Yolken, M.D., Yuanzhang Li, Ph.D., and Natalya S. Weber, M.D., M.P.H. Selected Infectious Agents and Risk of Schizophrenia Among U.S. Military Personnel Am J Psychiatry 2008; 165:99-106

2. Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology, 4th ed., McGraw Hill, 7227. ISBN 0838585299.

3. Brown AS, Cohen P, Greenwald S, Susser E. Nonaffective psychosis after prenatal exposure to rubella. Am J Psychiatry (2000) 157::438443.

4. Buka SL, Tsuang MT, Torrey EF, Klebanoff MA, Bernstein D, Yolken RH. Maternal infections and subsequent psychosis among offspring. Arch Gen Psychiatry (2001) 58::10321037

5. Suvisaari J, Haukka J, Tanskanen A, Hovi T, Lonnqvist J. Association between prenatal exposure to poliovirus infection and adult schizophrenia. Am J Psychiatry (1999) 156::11001102.

6. E. Fuller Torrey, John J. Bartko, Zhao-Rong Lun and Robert H. Yolken Antibodies to Toxoplasma gondii in Patients With Schizophrenia: A Meta-Analysis
Schizophrenia Bulletin 2007 33(3):729-736; doi:10.1093/schbul/sbl050

7. Berdoy M, Webster JP, Macdonald DW (2000). Fatal attraction in rats infected with Toxoplasma gondii. Proc. Biol. Sci. 267 (1452): 1591-4. doi:10.1098/rspb.2000.1182.

8. Kevin D. Lafferty Can the common brain parasite, Toxoplasma gondii, influence human culture? Proceedings of the Royal Society, Biological Sciences DOI10.1098/rspb.2006.3641