Toxoplasma gondii infection and risk of Parkinson and Alzheimer diseases: A systematic review and meta-analysis on observational studies

In the past decade, Toxoplasma gondii infection has been recognized as a potential risk for many psychiatric and neurological disorders. We performed this systematic review and meta-analysis to evaluate the association between Toxoplasma infection and Parkinson’s and Alzheimer’s diseases. PubMed, Web of science, Scopus and Embase databases were searched up to September 30, 2018 for studies that reported risk of Parkinson’s and Alzheimer’s diseases associated with Toxoplasma infection. We used a random effects meta-analysis model to generate the pooled odds ratio (OR) with 95% confidence intervals (CIs). Eleven studies, including seven studies for Parkinson’s disease (428 patients and 540 controls) and four studies for Alzheimer’s disease (301 patients and 313 controls), were included in the meta-analysis. We found that there was no statistically significant association between Toxoplasma infection, as determined by IgG serology, IgM serology, and PCR with increased risk of Parkinson’s disease (OR, 1.14; 95% CI, 0.78–1.68), (OR, 1.61; 95% CI, 0.33–7.76) and (OR, 1.87; 95% CI, 0.43–8.05), respectively. The OR for association of Toxoplasma infection, based on IgG serology with Alzheimer’s patients, compared to control group, was (OR, 1.38; 95% CI, 0.99–1.92), demonstrating a marginally significant association between Toxoplasma infection and Alzheimer’s disease. Our findings do not support a general hypotheses regarding an associative relationship between Toxoplasma infection and Parkinson’s disease, but do support a marginally significant association between Toxoplasma infection and Alzheimer’s disease; this association should be investigated further through longitudinal and experimental studies.