A controlled prospective study of Toxoplasma gondii infection in individuals with schizophrenia: Beyond seroprevalence

Toxoplasma gondii (TG) infection is reportedly more frequent in schizophrenia. The interaction of the persisting parasite with the host's immune system involves T-cell/interferon-gamma induced degradation of tryptophan and provides a challenge to the host beyond a possible role in the etiology of schizophrenia. We hypothesized that TG infection is more frequent (serofrequency) and/or more intense (serointensity) in patients with schizophrenia or major depression compared to psychiatrically healthy controls. In addition, these measures are associated with the clinical course. We did a cross-sectional, prospective investigation of matched individuals with schizophrenia (n=277) and major depression (n=465), and of healthy controls (n=214). Serofrequency was comparable between the groups, but serointensity was significantly higher in the patients. In schizophrenia, serointensity was significantly positively associated with CRP levels and leukocyte counts, and first-episode patients yielded significantly higher serotiters. Immunomodulatory medication was associated with decreased serotiters. The route of infection might differ between patients and controls. Our results support increased host responses to TG infection in the patients, as well as increased titers in first-episode patients with schizophrenia; this may relate to the shifted T-helper1/2 status described in these patients. This study was supported by grant #01T-404 of The Stanley Medical Research Institute.