Toxoplasma gondii seropositivity increases risk for mild cognitive impairment

Toxoplasma gondii seropositivity appeared linked to mild cognitive impairment in multiple cognitive domains, according to results of a systematic review and meta-analysis published in JAMA Psychiatry.

“Several observational studies have reported neurocognitive changes associated with toxoplasmosis in humans; however, effect sizes and directions varied,” Lies de Haan, BSc, of the department of psychiatry at the University of Amsterdam in the Netherlands, and colleagues wrote. “Meta-analyses have suggested an association between T. gondii and neuropsychiatric disorders, particularly schizophrenia. Although meta-analytic findings have not found an association between T. gondii and [ADHD], one recent case-control study did report an association.”

Moreover, a prior study linked T. gondii exposure to an increase in motor vehicle crashes and suicide attempts. De Haan and colleagues sought to determine whether and how significantly T gondii seropositivity affected cognitive function among otherwise healthy individuals. They systematically searched five databases and identified studies published between database inception and June 7, 2019, that featured an analysis of cognitive function among health individuals who had data available on T. gondii seropositivity. The researchers included the search terms toxoplasmosis, neurotoxoplasmosis, Toxoplasma gondii, cognition disorder, neuropsychological and psychomotor performance. Performance on neuropsychological tests that assessed cognitive function served as the main outcome.

In the meta-analysis, De Haan and colleagues included 13 studies with 13,289 total healthy participants (mean age, 46.7 years; 49.6% men) with and without T. gondii seropositivity. Those without seropositivity exhibited favorable functioning in the cognitive domains of processing speed (SMD = 0.12; 95% CI, 0.05-0.19), working memory (SMD = 0.16; 95% CI, 0.06-0.26), short-term verbal memory (SMD = 0.18; 95% CI, 0.09-0.27) and executive functioning (SMD = 0.15; 95% CI, 0.01-0.28). Those with seropositivity had significantly worse cognitive function in all analyzed domains. Results of a meta-regression analysis showed a significant correlation between older age and executive functioning (P = .01). The researchers noted little evidence of publication bias.

“Based on the present findings and those of previous meta-analyses, examining the association of T. gondii seropositivity with motor vehicle crashes, suicide attempts and the prevalence of psychiatric disorders, public health programs to prevent T. gondii infection are warranted,” De Haan and colleagues wrote. “These programs might, at a minimum, consist of hygienic measures, especially after human contact with contaminated sources.”