Parasite Common to Cats Linked to Human Psychosis

Toxoplasma gondii (T.gondii), a common parasite found in the stomach of cats, may alter human behavior and lead to psychotic symptoms similar to those displayed by persons with schizophrenia, according to a study by researchers from the Stanley Medical Research Institute and Johns Hopkins University Medical Center.

Research shows that somewhere between 25 and 50 percent of the world's human population may be infected with Toxoplasma, which is a leading cause of stillbirths and primary infection in pregnant women. T. gondii is common in both domesticated and wild cats and is believed to be passed on to humans through the cat feces and undercooked meat.

Since 1953, 19 studies have shown the presence of T. gondii antibodies in persons with schizophrenia and other severe psychiatric disorders, according to information contained in this latest study.

In many of the studies, the parasite was linked to psychological and behavioral changes in humans when T. gondii was passed by a mother to her unborn child. However, two other studies have also linked exposure to cats in childhood as a risk factor for the development of schizophrenia.

The Stanley Medical and Johns Hopkins study goes on to say that the relationship between schizophrenia and other psychiatric diseases and T. gondii has not been definitively established. The study's authors believe that "establishing the role of T. gondii in the etiopathogenesis of schizophrenia might lead to new medications for the treatment and prevention of the disease."

Currently, some medications used to treat schizophrenia are also used to inhibit the role of T. gondii in cell culture. A study conducted by scientists at the Imperial College of London in 2006 showed that the drugs Haloperidol, an anti-psychotic, and Valporic acid, a mood stabilizer, reduced the behavioral symptoms of T. gondii in rats.

Toxoplasma's Effect on Human Cultural Traits

A 2006 study from the University of California, Santa Barbara concluded that in populations where the parasite is very common, "mass personality modification could result in cultural change."

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Toxoplasma is associated with different, often opposite, behavioral changes in men and women, but both genders exhibit proneness to guilt (a form of neuroticism). Kevin Lafferty, the UCSB study author and scientist, found that countries with high Toxoplasma gondii prevalence had a higher aggregate neuroticism score, and western nations with high prevalence also scored higher in the 'neurotic' cultural dimensions of 'masculine' sex roles and uncertainty avoidance.

Lafferty said this research may just be the tip of the iceberg for how Toxoplasma affects humans. "There could be a lot more to this story," he said in a news release. "Different responses to the parasite by the men and women could lead to many additional cultural effects that are, as yet, difficult to analyze."