Association of Toxoplasma gondii Seropositivity With Cognitive Function in Healthy People

Importance

The parasiteToxoplasma gondiihas been associated with behavioral alterations and psychiatric disorders. Studies investigating neurocognition in people withT gondiiinfection have reported varying results. To systematically analyze these findings, a meta-analysis evaluating cognitive function in healthy people with and withoutT gondiiseropositivity is needed.

Objective

To assess whether and to what extentT gondiiseropositivity is associated with cognitive function in otherwise healthy people.

Data Sources

A systematic search was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline. A systematic search of PubMed, MEDLINE, Web of Science, PsycInfo, and Embase was performed to identify studies from database inception to June 7, 2019, that analyzed cognitive function among healthy participants with available data onT gondiiseropositivity. Search terms included toxoplasmosis,neurotoxoplasmosis,Toxoplasma gondii,cognition disorder,neuropsychological, andpsychomotor performance.

Study Selection

Studies that performed cognitive assessment and analyzedT gondiiseroprevalence among otherwise healthy participants were included.

Data Extraction and Synthesis

Two researchers independently extracted data from published articles; if needed, authors were contacted to provide additional data. Quantitative syntheses were performed in predefined cognitive domains when 4 independent data sets per domain were available. Study quality, heterogeneity, and publication bias were assessed.

Main Outcomes and Measures

Performance on neuropsychological tests measuring cognitive function.

Results

The systematic search yielded 1954 records. After removal of 533 duplicates, an additional 1363 records were excluded based on a review of titles and abstracts. A total of 58 full-text articles were assessed for eligibility (including reference list screening); 45 articles were excluded because they lacked important data or did not meet study inclusion or reference list criteria. The remaining 13 studies comprising 13 289 healthy participants (mean [SD] age, 46.7 [16.0] years; 6586 men [49.6%]) with and withoutT gondiiseropositivity were included in the meta-analysis. Participants withoutT gondiiseropositivity had favorable functioning in 4 cognitive domains: processing speed (standardized mean difference [SMD], 0.12; 95% CI, 0.05-0.19;P = .001), working memory (SMD, 0.16; 95% CI, 0.06-0.26;P = .002), short-term verbal memory (SMD, 0.18; 95% CI, 0.09-0.27;P < .001), and executive functioning (SMD, 0.15; 95% CI, 0.01-0.28;P = .03). A meta-regression analysis found a significant association between older age and executive functioning (Q = 6.17;P = .01). Little suggestion of publication bias was detected.

Conclusions and Relevance

The study’s findings suggested thatT gondiiseropositivity was associated with mild cognitive impairment in several cognitive domains. Although effect sizes were small, given the ubiquitous prevalence of this infection globally, the association with cognitive impairment could imply a considerable adverse effect at the population level. Further research is warranted to investigate the underlying mechanisms of this association.