Large-scale study of Toxoplasma and Cytomegalovirus shows an association between infection and serious psychiatric disorders

Abstract Background Common infectious pathogens have been associated with psychiatric disorders, self-violence and risk-taking behavior. Methods This case-control study reviews register data on 81,912 individuals from the Danish Blood Donor Study to identify individuals who have a psychiatric diagnosis (N=2,591), have attempted or committed suicide (N=655), or have had traffic accidents (N=2,724). For all cases, controls were frequency matched by age and sex, resulting in 11,546 participants. Plasma samples were analyzed for immunoglobulin G (IgG) antibodies against Toxoplasma gondii and cytomegalovirus (CMV). Results T. gondii was detected in 25·9% of the population and was associated with schizophrenia (odds ratio [OR], 1·47; 95% confidence interval [CI], 1·03–2·09). Accounting for temporality, with pathogen exposure preceding outcome, the association was even stronger (IRR, 2·78; 95% CI, 1·27–6·09). A very weak association between traffic accident and toxoplasmosis (OR, 1·11; 95% CI, 1·00–1·23, p = 0.054) was found. CMV was detected in 60·8% of the studied population and was associated with any psychiatric disorder (OR, 1·17; 95% CI, 1·06–1·29), but also with a smaller group of neurotic, stress-related, and somatoform disorders (OR, 1·27; 95% CI, 1·12–1·44), and with attempting or committing suicide (OR, 1·31; 95% CI, 1·10–1·56). Accounting for temporality, any psychiatric disorder (IRR, 1·37; 95% CI, 1·08–1·74) and mood disorders (IRR, 1·43; 95% CI, 1·01–2·04) were associated with exposure to CMV. No association between traffic accident and CMV (OR, 1·06; 95% CI, 0·97–1·17) was found. Conclusions This large-scale serological study is the first study to examine temporality of pathogen exposure and to provide evidence of a causal relationship between T. gondii and schizophrenia, and between CMV and any psychiatric disorder.