A recent study published in the European Journal of Neurology concluded that Toxoplasma gondii infection may have a protective effect in the development of multiple sclerosis (MS).

The systematic review and meta-analysis by Cicero et al included 7 articles, with a total of 752 MS cases and 1282 controls. The study authors found a pooled odds ratio of 0.68 for the association between MS and anti-T gondii antibodies (95% CI, 0.50-0.93) with a moderate heterogeneity (I2=47%, Cochran’s Q test P =0.06).

Cicero et al explained, “According to the hygiene hypothesis, exposure to parasites (such as helminths) especially in the young age has been associated with lower risk of developing MS, probably due to the interactions that multiple and chronic infections establish with the host immune system.”

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This association has been demonstrated both epidemiologically and experimentally. Researchers believe that chronic interaction between the helminths and the host immune system promotes an immunosuppressive immunological environment that facilitates the survival of the parasite.

A previous meta-analysis that aimed to evaluate the role of T gondii in MS showed similar trends, but the results did not show statistical significance. Five of the studies analyzed were common to both meta-analyses.

However, Cicero et al discussed a number of limitations to their study. For instance, the small number of studies included did not allow the evaluation of additional factors that might interfere with the association between T gondii infection and MS. In addition, causality could not be established since the studies were performed retrospectively. Hence, it was unknown whether T gondii exposure occurred before or after the development of MS.


Cicero CE, Allibrio FE, Giuliano L, Luna J, Preux PM, Nicoletti A. Toxoplasma gondii and multiple sclerosis: a systematic review and meta‐analysis. Eur J Neurol. Published online August 9, 2021. doi:10.1111/ene.15055