Exposure to Microorganisms and Adult Psychiatric Disorders: The Case for a Causal Role of Toxoplasma gondii

Abstract

Since the 1970s there has been an increasing interest in infectious agents as possible causes of serious mental illness. The microorganism which has been most intensively studied is Toxoplasma gondii, a parasite carried by felines. Several lines of research have suggested that T. gondii is associated with schizophrenia: increased prevalence of T. gondii antibodies in individuals with this disease, and in mothers who give birth to individuals who later are so diagnosed; increased childhood contact with cats by individuals who later are so diagnosed; the fact that T. gondii affects several neurotransmitters and makes dopamine; and the fact that some antipsychotics suppress T. gondii. But is there any evidence that this association is etiological? Austin Bradford Hill published criteria for assessing possible etiological associations between environmental factors and complex diseases. His criteria include strength of association, consistency of findings, specificity of findings, temporality of relationship, biological gradient, plausibility of relationship, coherence of relationship, analogy with other data, and experimental data. Using these criteria, it is concluded that an etiological relationship between T. gondii and some cases of schizophrenia is reasonable. (PsycInfo Database Record (c) 2022 APA, all rights reserved)