Impact of Toxoplasma gondii Seropositivity on Thyroid Function and Anti-TPO Antibody Status

Abstract Background: Thyroid dysfunction is one of the most common endocrine illnesses worldwide, with autoimmune mechanisms significantly contributing to its aetiology. Toxoplasma gondii, a prevalent intracellular parasite, has been proposed as a potential catalyst for autoimmune thyroid disorders (AITDs), however its function remains inadequately comprehended. Objective: This study sought to examine the correlation between Toxoplasma gondii infection and thyroid dysfunction, specifically with the positivity of anti-thyroid peroxidase (anti-TPO) antibodies. Methods: A cross-sectional investigation was executed in Kirkuk, Iraq, from October 1, 2024, to April 30, 2025, encompassing 100 patients with thyroid dysfunction (13 with hyperthyroidism and 87 with hypothyroidism) and 50 healthy controls. Serum samples were examined for thyroid hormones (TSH, T3, T4), anti-TPO antibodies (CLIA), and T. gondii-specific IgM and IgG antibodies (ELISA). Results: Marked disparities in age distribution were seen between patients and controls (p = 0.0003), with hyperthyroidism prevalent in individuals over 55 years, and hypothyroidism more common in middle-aged cohorts. Despite a higher prevalence among females, the sex differences were not statistically significant (p = 0.083). Anti-TPO positivity was markedly elevated in patients (23%) vs to controls (0%) (p = 0.0025). The infection of T. gondii shown a substantial correlation with thyroid dysfunction, especially in Anti-TPO positive patients, where the co-positivity of IgM/IgG was 34.78% compared to 5.19% in Anti-TPO negative individuals (p = 0.0001). Co-positivity for CMV IgM/IgG was significantly greater in Anti-TPO positive patients (34.78%) than in negative patients (2.60%) (p = 0.0001). In seronegative individuals for T. gondii, those who tested positive for Anti-TPO exhibited a substantially greater mean age (55.71 ± 12.23 years) compared to those who tested negative for Anti-TPO (39.59 ± 14.78 years; p = 0.016). Moreover, infection markers exhibited a robust correlation with Anti-TPO positivity by gender, with Anti-TPO positive males demonstrating the highest co-positivity rates for both T. gondii and CMV (66.67%). Conclusion: The results suggest a possible immunopathogenic involvement of Toxoplasma gondii infection in autoimmune thyroid dysfunction, specifically hypothyroidism linked to anti-TPO positive.