Journal of Preventive Medicine

Introduction
Toxoplasmosis is a parasitic disease caused by Toxoplasma gondii. The final hosts of this protozoan are cats and felines, and their intermediate hosts are humans and other animals. T. gondii infection is associated with many disorders in different human organs. If a mother is infected with toxoplasmosis for the first time during pregnancy, there is a possibility that the fetus will also be infected. If the mother is infected in the first trimester of pregnancy, when the parasite passes through the placenta and reaches the fetus, it will cause severe complications such as miscarriage in most cases. If the parasite is transmitted in the second trimester, eye symptoms such as retinochoroiditis, microcephaly and mental retardation will be observed. Its transmission in the third trimester causes lymphadenopathy, hepatosplenomegaly, hepatomegaly, eye disorders, and calcified lesions in the brain. In people with weakened immunity, the disease is more dangerous and develop more severe symptoms. The relationship between toxoplasmosis and thyroid dysfunction has not been fully evaluated and there is no comprehensive information on this relationship. The purpose of this study is to investigate the relationship between toxoplasmosis and thyroid dysfunction.

Methods
This case-control study was conducted in one of the medical centers in Yazd, Iran. A total of 82 patients (78 women and 4 men) and 801 healthy people (747 women and 54 men) were included in the study. The control or healthy people were selected from among those visited the clinical laboratory of a medical center in Yazd and were negative for hypothyroidism and hyperthyroidism. The criteria for entering the study for patients were age ≥15 years and having a history of hypothyroidism or hyperthyroidism. Diagnosis of thyroid gland disorders was done by responsible doctors based on clinical symptoms and diagnosis of abnormally high/low thyroid stimulating hormone and free thyroxine level. 
A blood sample (5 mL) was taken from each participant and left for 2 hours at room temperature to clot. Then the samples were centrifuged at 3000 rpm for 10 minutes to obtain the serum. The collected serum was kept at -20 °C until use. According to the instructions of the manufacturer of the kit, the optical density of IgG antibody and thyroid hormones was read at a wavelength of 450 nm after 15 minutes using an automatic microplate reader. Then, the cut-off value of the ELISA test was determined for positive and negative results. High anti-T. gondii IgG antibody titers of more than 200 IU/mL were considered positive in patients with thyroid deficiency, and titers <200 IU/mL were considered negative.

Results
In this study, anti-T. gondii  IgG antibody was found in 12(14.63%) out of 82 patients with thyroid dysfunction and in 146(18.23%) out of 801 healthy individuals. No statistically significant difference was observed in the prevalence of anti-Toxoplasma IgG antibodies in patients with thyroid dysfunction compared to healthy subjects (OR=0.77; 95% CI: 0.37-1.47, P=0.54). Six patients (12.5%) out of 48 patients with hyperthyroidism were positive for anti-T. gondii IgG antibody.
The frequency of high anti-T. gondii IgG antibody titers (>200 IU/mL) in patients with thyroid dysfunction was similar to that in healthy control group (6.82 vs 33.801; OR=1.79, 95% CI, 0.59%, 4.51%, P=0.25). In patients with hypothyroidism (3.34 vs 33.801; OR=2, 95% CI, 0.78%, 7.46%, P=0.057) and hyperthyroidism (5.48 vs 33.801; OR=2.7, 95% CI, 0.78%, 7.46%, P=0.057), the frequency was also similar to that in healthy control group. There was no significant difference in the serum level of T. gondii either between people with hypothyroidism and healthy people (P=0.54) nor between people with hyperthyroidism and healthy people (P=0.99). 

Conclusion
In the present study, the findings did not show a significant difference between the serum prevalence of T. gondii in patients with hypothyroidism and hyperthyroidism compared to healthy people. Based on these observations, we recommend further prospective research to clarify the relationship between thyroid dysfunction and toxoplasmosis infection.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of Birjand University of Medical Sciences (Code: IR.BUMS.REC.1399.174).

Funding
This study was supported by Birjand University of Medical Sciences, Birjand, Iran.

Authors' contributions
Conceptualization and supervision: Roghayeh Norouzi, and Abolghasem Siyadatpanah; Methodology: Roghayeh Norouzi, and Seyed Jafar Adnani Sadati; Investigation: Roghayeh Norouzi, and Reza Ahmadi; Writing the  original draft: Reza Afzalipour, and Javad Sadeghinasab; Review and editing: Roghayeh Norouzi, and Ahmad Negahban; Funding acquisition and resources: Abolghasem Siyadatpanah.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgements
The authors thank all colleagues working in Parasitology Department at the Birjand University of Medical Sciences, Birjand, Iran.

References

1. Dubey JP, Darrington C, Tiao N, Ferreira LR, Choudhary S, Molla B, et al. Isolation of viable Toxoplasma gondii from tissues and feces of cats from Addis Ababa, Ethiopia. J Parasitol. 2013; 99(1):56-8. [DOI:10.1645/GE-3229.1] [PMID]
2. Asgari Q, Mehrabani D, Motazedian M, Kalantari M, Nouroozi J, Adnani Sadati S. The viability and infectivity of Toxoplasma gondii tachyzoites in dairy products undergoing food processing. Asian J Anim Sci. 2011; 5(3):202-7. [DOI:10.3923/ajas.2011.202.207]
3. Pappas G, Roussos N, Falagas ME. Toxoplasmosis snapshots: Global status of Toxoplasma gondii seroprevalence and implications for pregnancy and congenital toxoplasmosis. Int J Parasitol. 2009; 39(12):1385-94. [DOI:10.1016/j.ijpara.2009.04.003] [PMID]
4. Mohaghegh MA, Yazdani H, Hadipour M, Namdar F, Azami M, Kalani H, et al. Seroprevalence of Toxoplasma gondii infection among patients admitted to Al-Zahra Hospital, Isfahan, Iran. J Ayub Med Coll Abbottabad. 2015; 27(4):767-70. [PMID]
5. Omidian M, Asgari Q, Bahreini MS, Moshki S, Sedaghat B, Adnani Sadati SJ. Acute toxoplasmosis can increase serum dopamine level. J Parasitic Dis. 2022; 46(2):337-42. [DOI:10.1007/s12639-021-01447-1] [PMID]
6. Dubey JP. History of the discovery of the life cycle of Toxoplasma gondii. Int J Parasitol. 2009; 39(8):877-82. [DOI:10.1016/j.ijpara.2009.01.005] [PMID]
7. Scallan E, Hoekstra RM, Angulo FJ, Tauxe RV, Widdowson MA, Roy SL, et al. Foodborne illness acquired in the United States- Major pathogens. Emerg Infect Dis. 2011; 17(1):7-15. [DOI:10.3201/eid1701.P11101] [PMID]
8. Bresciani KDS, Galvão ALB, Vasconcellos ALd, Soares JA, Matos LVSd, Pierucci JC, et al. Relevant aspects of human toxoplasmosis. Res J Infect Dis. 2013; 1(1):1-7. [Link]
9. Asgari Q, Sarnevesht J, Kalantari M, Sadat SJ, Motazedian MH, Sarkari B. Molecular survey of Toxoplasma infection in sheep and goat from Fars province, Southern Iran. Trop Anim Health Prod. 2011; 43(2):389-92. [DOI:10.1007/s11250-010-9704-1] [PMID]
10. Dubey JP, Jones JL. Toxoplasma gondii infection in humans and animals in the United States. Int J Parasitol. 2008; 38(11):1257-78. [DOI:10.1016/j.ijpara.2008.03.007] [PMID]
11. Flegr J, Prandota J, Sovičková M, Israili ZH. Toxoplasmosis-a global threat. Correlation of latent toxoplasmosis with specific disease burden in a set of 88 countries. Plos One. 2014; 9(3):e90203. [DOI:10.1371/journal.pone.0090203] [PMID]
12. Zouei N, Shojaee S, Mohebali M, Keshavarz H. The association of latent toxoplasmosis and level of serum testosterone in humans. BMC Res Notes. 2018; 11(1):365. [DOI:10.1186/s13104-018-3468-5] [PMID]
13. Boelaert K, Franklyn JA. Thyroid hormone in health and disease. J Endocrinol. 2005; 187(1):1-15. [DOI:10.1677/joe.1.06131] [PMID]
14. Wasserman EE, Nelson K, Rose NR, Rhode C, Pillion JP, Seaberg E, et al. Infection and thyroid autoimmunity: A seroepidemiologic study of TPOaAb. Autoimmunity. 2009; 42(5):439-46. [DOI:10.1080/08916930902787716] [PMID]
15. Alvarado-Esquivel C, Torres-Castorena A, Liesenfeld O, García-López CR, Estrada-Martínez S, Sifuentes-Alvarez A, et al. Seroepidemiology of Toxoplasma gondii infection in pregnant women in rural Durango, Mexico. J Parasitol. 2009; 95(2):271-4. [DOI:10.1645/GE-1829.1] [PMID]
16. Liu DC, Lin CS, Seshan V. [AIDS complicated with disseminated toxoplasmosis: A pathological study of 9 autopsy cases (Chinese)]. Zhonghua Bing Li Xue Za Zhi. 1994; 23(3):166-9. [PMID]
17. Tozzoli R, Barzilai O, Ram M, Villalta D, Bizzaro N, Sherer Y, et al. Infections and autoimmune thyroid diseases: Parallel detection of antibodies against pathogens with proteomic technology. Autoimmun Rev. 2008; 8(2):112-5. [DOI:10.1016/j.autrev.2008.07.013] [PMID]
18. Stahl W, Kaneda Y. Impaired thyroid function in murine toxoplasmosis. Parasitology. 1998; 117 (Pt 3):217-22. [DOI:10.1017/S003118209800300X] [PMID]
19. Salman Y, Mustafa WG. Correlation between Toxoplasma gondii and Thyroid function hormone levels in sera of patients attending private clinics and laboratories in Kirkuk City. Int J Plant Biol. 2014; 1(4):299-306. [Link]
20. Al-Ezzy AIA, Abood WN. Immunoenocrinology Association of toxoplasma gondii and thyroid hormins in Iraqi Patients with clinical manifestatons of toxoplasmosis. Int J Pharma Bio Sci. 2016; 7(1):359-69. [Link]
21. Alvarado-Esquivel C, Ramos-Nevarez A, Guido-Arreola CA, Cerrillo-Soto SM, Pérez-Álamos AR, Estrada-Martínez S, et al. Association between Toxoplasma gondii infection and thyroid dysfunction: A case-control seroprevalence study. BMC Infect Dis. 2019; 19(1):826. [DOI:10.1186/s12879-019-4450-0] [PMID]
22. Al-Issawi TAM, Mohammed AS. Effects of Infection with Toxoplasma Gondii to the Levels of Thyroid Hormones. Eur J Mol Clin Med. 2020; 7(1):110-4. [Link]