Tehran University of Medical Sciences Iranian Journal of Parasitology 1735-7020 17 3 2022 09 05 325 331 Mehdi Zarean Department of Parasitology and Mycology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran Pietro Mastroeni Department of Veterinary Medicine, Cambridge University, Cambridge, United Kingdom Elham Moghaddas Department of Parasitology and Mycology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran Bibi Razieh Hosseini Farash Department of Parasitology and Mycology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran Amene Raouf-Rahmati Department of Parasitology and Mycology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran Jamshid Jamali Department of Biostatistics and Epidemiology, School of Health, Mashhad University of Medical Sciences, Mashhad, Iran Hossein Azadeh Department of Internal Medicine, Rheumatology Division, Orthopaedic Research Center, Mazandaran University of Medical Sciences, Sari, Iran Vahideh Kam Department of Parasitology and Mycology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran 2022 01 04 2022 07 31 Background: Toxoplasmosis is a zoonotic disease caused by the parasite Toxoplasma gondii, a cosmopolitan intracellular parasite. It can be a risk factor for autoimmune diseases, including rheumatoid arthritis (RA). This study was designed to investigate the possible association between serological history of T. gondii infection and defined clinical manifestation of RA in Northeast of Iran. Methods: Overall, serum samples were collected from 50 RA patients and 40 healthy controls, from Qaem Hospital in Mashhad City, northeastern Iran in 2018. Seroprevalence of T. gondii infection was determined by ELISA. Results: The prevalence of anti -T. gondii IgG in RA patients 48% (24.50) was significantly higher than the control group 10% (4.40) (P <0.001). Erythrocyte sedimentation rate (ESR), anti-cyclic citrullinated peptide (anti-CCP) and (rheumatoid factor) RF levels between the RA and control groups (P <0.01). Control group were matched with patients for age, gender and living area. Conclusion: Given that a high correlation has been demonstrated between positivity rate of anti-T. gondii IgG and RA in Northeastern Iran, further studies will be necessary to clarify the pathogenesis of T. gondii among these patients. https://ijpa.tums.ac.ir/index.php/ijpa/article/view/3543 https://ijpa.tums.ac.ir/index.php/ijpa/article/download/3543/1227