Toxoplasma gondii affects trait anxiety in adult ADHD

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 = 0.015). 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.