The impact of Toxoplasma gondii infection on the risk of developing paranoid schizophrenia – a literature review

Infection with Toxoplasma gondii (TG) is common in humans. This review synthesizes evidence on the association between latent TG infection and paranoid schizophrenia, and evaluates specificity and clinical implications. PRISMA 2020-compliant review. PubMed, Scopus, Web of Science, and Google Scholar searched (2000–2025; Polish/English) with keywords: Toxoplasma gondii, paranoid schizophrenia, neuroinflammation. Included original and review studies; excluded case reports and non-peer-reviewed items; prioritized post-2017. Comparators: people without mental disorders and those with other disorders (bipolar disorder, depression, obsessive-compulsive disorder) to gauge specificity. Terminology: people with mental disorders. Many studies report higher TG seropositivity in schizophrenia than in the general population. Proposed mechanisms: dopaminergic modulation, altered tryptophan metabolism, and chronic neuroinflammation; animal models corroborate behavioral and neurochemical changes. Clinically, seropositivity may relate to a more severe course. The association is not fully specific: strongest in schizophrenia, weaker in bipolar disorder and obsessive-compulsive disorder, inconsistent in depression. Toxoplasma gondii may modify the course of paranoid schizophrenia; the relationship is biologically plausible but causality remains unproven. Meta-analyses indicate OR about 2-3 with substantial heterogeneity. Further translational studies and therapeutic implications should be explored.