Background: Toxoplasma gondii is an intracellular protozoan coccidian parasite, that can establish a widespread infection in people with autoimmune disorders.
Rheumatoid arthritis is an autoimmune inflammatory disorder in which biological therapy is one of the treatment modalities. This study aims to evaluate Toxoplasma gondii IgM antibody seropositivity in Rheumatoid arthritis patients in Mosul city who were under biological therapy.
 Methods: A case control study was conducted at Mosul City in Iraq, enrolled 190 participants who were divided into 2 groups, 95 patients had RA on biological therapy and the other 95 participants were a healthy control group. Using the enzyme-linked immunosorbent assay technique, anti-Toxoplasma IgM antibodies have been identified in the sera of ninety-five rheumatoid arthritis patients undergoing biological therapy for six months, as well as in the serum of ninety-five healthy controls. 
Results: Anti-Toxoplasma IgM antibodies were detected in (17%) of RA patients and only (2.1%) of controls (P=0.0008). The mean value of IgM antibody was 29.232 IU/mL in rheumatoid patients versus 14.59 IU/mL in controls (P=0.0463). The highest Toxoplasma IgM antibody level was in the age group (31-49 years) with (P=0.0145). There was no significant connection between seropositivity and the three types of biological therapy (P=0.389). 

 Conclusion: There is an association between long-term biological treatments for RA and the onset of toxoplasmosis.