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

Abstract

Background: Thyroid dysfunction is among the most prevalent endocrine disorders globally, with autoimmune processes playing a significant etiological role. Toxoplasma gondii, a widespread intracellular parasite, has been suggested as a potential trigger for autoimmune thyroid diseases (AITDs), yet its role remains poorly understood. Objective: This study aimed to investigate the association between Toxoplasma gondii infection and thyroid dysfunction, particularly in relation to anti-thyroid peroxidase (anti-TPO) antibody positivity. Methods: A cross sectional study was conducted in Kirkuk, Iraq, from October 1, 2024, to April 30, 2025, involving 100 patients with thyroid dysfunction (13 with hyperthyroidism and 87 with hypothyroidism) and 50 healthy controls. Serum samples were analyzed for thyroid hormones (TSH, T3, T4), anti-TPO antibodies (CLIA), and T. gondii-specific IgM and IgG antibodies (ELISA). Results:  Significant differences were found in age distribution between patients and controls (p = 0.0003), with hyperthyroidism predominating in patients >55 years, and hypothyroidism among middle-aged groups. Although females were more commonly affected, sex differences were not statistically significant (p = 0.083). Anti-TPO positivity was significantly higher among patients (23%) compared to controls (0%) (p = 0.0025). T. gondii infection* showed significant association with thyroid dysfunction, particularly among Anti-TPO positive patients where IgM/IgG co-positivity was 34.78% versus 5.19% in Anti-TPO negatives (p = 0.0001). CMV IgM/IgG co-positivity was also markedly higher in Anti-TPO positive patients (34.78%) compared to negatives (2.60%) (p = 0.0001). Among seronegative patients for T. gondii, Anti-TPO positives had a significantly higher mean age (55.71 ± 12.23 years) than Anti-TPO negatives (39.59 ± 14.78 years; p = 0.016). Furthermore, infection markers were strongly associated with Anti-TPO positivity by gender, with Anti-TPO positive males showing the highest co-positivity rates for both T. gondii and CMV (66.67%). Conclusion: The findings indicate a potential immunopathogenic role of Toxoplasma gondii infection in autoimmune thyroid dysfunction, particularly hypothyroidism associated with anti-TPO positivity.