ORIGINAL RESEARCH article
Front. Psychiatry
Sec. ADHD
This article is part of the Research Topic15 Years of Frontiers in Psychiatry - Neurodevelopmental DisordersView all 4 articles
Toxoplasma gondii affects trait anxiety in adult ADHD
Provisionally accepted
- 1Department of Psychiatry and Psychotherapy, University Hospital Bonn, University of Bonn, Bonn, Germany
- 2School of Medicine and Health Sciences, Medical Campus University of Oldenburg, Oldenburg, Germany
- 3University Institute of Clinical Chemistry and Laboratory Medicine, Klinikum Oldenburg, Oldenburg, Germany
- 4Institute for Laboratory Diagnostics and Microbiology, Klinikum Oldenburg, School of Medicine and Health Sciences, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
Select one of your emails
You have multiple emails registered with Frontiers:
Notify me on publication
Please enter your email address:
If you already have an account, please login
You don't have a Frontiers account ? You can register here
Background/Objective: Growing evidence emerges that Toxoplasma gondii (T. gondii) is associated with mental disorders like anxiety disorders or attention-deficit/hyperactivity disorder (ADHD). In ADHD patients around 25% suffer from comorbid anxiety disorders. As the impact of a latent T. gondii infection on anxiety in adult ADHD remains unknown, this study aims to investigate this relationship. Methods: In a case-control study, including 140 participants, venous blood samples were taken of 70 adult ADHD patients and 70 controls for serological analysis of markers of infection and inflammation (leukocytes, C-reactive protein, anti-T. gondii immunoglobulin M (IgM) and anti-T. gondii immunoglobulin G (IgG) (seropositivity), IgG titers (serointensity) as well as anti-T. gondii IgG avidity. The influences on state and trait anxiety were explored using the State-Trait-Anxiety Inventory (STAI). Results: Seropositivity was significantly associated with the leukocyte count in all participants (n=140, p=0.004). Moreover, regression analysis revealed a significant association of seropositivity and serointensity with trait anxiety but not with state anxiety: trait anxiety was significantly lower in seropositive ADHD patients compared to seronegative subjects with ADHD (n=70, p=0.029). In addition, trait anxiety scores decreased in an IgG-dependent manner in all participants (n=140, p=0.028) as well as in the ADHD group (n=70, p=0.014). Comorbid anxiety disorders in ADHD were not associated with latent T. gondii infection. Conclusion: Our data is the first revealing an association between T. gondii and trait anxiety in a serointensity-dependent manner in individuals with ADHD. Further research is needed to clarify the clinical impact of the observed lower trait anxiety in individuals with ADHD and latent T. gondii infection.
Keywords: ADHD, Anxiety Disorders, state anxiety, State-Trait-Anxiety Inventory, Toxoplasma gondii, trait anxiety
Received: 12 Dec 2025; Accepted: 30 Jan 2026.
Copyright: © 2026 Lam, Carl, Kohse and Philipsen. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Alexandra Philomena Lam
Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.