M22. IGG ANTIBODIES TO TOXOPLASMA GONDII ARE ASSOCIATED WITH INCREASED LONG-TERM RISK FOR PSYCHOSIS IN INDIVIDUALS AT ULTRA-HIGH RISK FOR PSYCHOSIS

BACKGROUND: The prevalence of antibodies to Toxoplasma gondii, a ubiquitous parasitic protozoan causing the infectious disease toxoplasmosis, is increased in patients with psychotic disorders compared to the general population. We have previously shown that antibody titers for T.gondii correlate with the severity of positive symptoms in young people at ultra-high risk (UHR) for psychosis, suggesting that infection with T. gondii may be relevant to the manifestation of psychosis. However, it is unclear if T. gondii antibodies represent a risk factor for psychosis onset or non-psychotic outcome in UHR individuals. The aim of the present study was to examine whether seropositivity for T.gondii is associated with transition to psychosis and other outcomes in young people at UHR for psychosis. METHODS: The study sample consisted of 96 individuals at UHR for psychosis who were referred to the Personal Assistance and Crisis Evaluation (PACE) clinic in Melbourne, Australia, between 2001 and 2004, consented to optional blood tests for infectious agents and were followed up for up to 10 years after baseline (median (interquartile range) duration of follow-up: 7.15 (3.14 – 7.72) years). Serum IgG antibodies to six viral and parasitic pathogens (Toxoplasma gondii, Herpes Simplex Virus Type 1 and 2, Cytomegalovirus, Epstein Barr Virus, Varicella-Zoster Virus) were measured at baseline. Outcome measures included transition to psychosis, general psychiatric symptomatology and positive psychotic symptoms (BPRS), negative symptoms (SANS), depressive symptoms (HAM-D), anxiety symptoms (HAM-A) and functioning (SOFAS and GAF). Cox proportional hazards regression and linear regression models were used to examine the associations of seropositivity and antibody titers at baseline and transition to psychosis and other outcomes at follow-up. RESULTS: A total of 17 individuals (17.7%) were seropositive for Toxoplasma gondii at baseline. The rate of transition to psychosis was higher among seropositive (35.7%) compared to seronegative participants (14.6%), although this was not statistically significant (p=0.101). Antibody titers (IgG) for Toxoplasma gondii were significantly higher at baseline in participants who later transitioned to psychosis (1.34 ± 1.36 vs. 0.79 ± 0.73, p=0.027). Seropositivity for T.gondii IgG at baseline significantly predicted transition to psychosis within the follow-up duration (hazard ratio [HR]=3.61, 95%CI 1.08 – 12.00, p=0.036). Toxoplasma IgG at baseline were significantly associated with higher BPRS scores at follow-up in participants who were seropositive at baseline (Beta=6.38, 95%CI 0.43 – 12.34, p=0.038). No significant associations were found between antibodies to other pathogens and outcome, or between antibodies to Toxoplasma gondii and any other outcomes. DISCUSSION: Our findings suggest that the presence of IgG class antibodies for Toxoplasma gondii is associated with a higher risk for psychosis transition in individuals at UHR for psychosis, but not with risk for other long-term outcomes. These observations provide support for the hypothesis that infection with Toxoplasma gondii may be an environmental risk factor for psychosis and suggest that IgG antibodies for Toxoplasma gondii in individuals at UHR for psychosis have prognostic relevance.