According to recent epidemiologic studies, infectious agents may lead to some cases of schizophrenia. Infections with Toxoplasma gondii, usually associated with pet cats, can modify behavior and neurotransmitter function in animals.

When it comes to humans, acute infection with the cat virus, ‘T. gondii’, can lead to psychotic symptoms resembling those exhibited by persons with schizophrenia. It has been found by two other studies that exposure to cats in childhood could lead to the development of schizophrenia.

According to authors E. Fuller Torrey, Robert H. Yolken and Wendy Simmons, "Cat ownership in childhood has now been reported in three studies to be significantly more common in families in which the child is later diagnosed with schizophrenia or another serious mental illness".

There have been reports of 19 studies of T. gondii antibodies in persons with schizophrenia and other severe psychiatric disorders since 1953; there were a higher percentage of antibodies in the affected persons in 18 studies and the difference was statistically significant in 11 studies.

It is unknown if there is any geographic connection between the prevalence of toxoplasmosis and the prevalence of schizophrenia. France has a high prevalence of Toxoplasma-infected persons; it was reported that France has first-admission rates for schizophrenia roughly 50% higher compared to those in England.

Military medical records were reviewed by Dr. Robert H. Yolken, the director of the Stanley Laboratory at Johns Hopkins University, and his colleagues. It was found that soldiers who developed schizophrenia were two times as likely as other soldiers to display signs of Toxoplasma infection in blood samples.