Tehran University of Medical Sciences Iranian Journal of Parasitology 1735-7020 15 2 2020 06 07 187 195 Fatemeh TABATABAIE Department of Parasitology and Mycology, School of Medicine, Iran University of Medical Sciences, Tehran, Iran Taher ELMI Department of Parasitology and Mycology, School of Medicine, Iran University of Medical Sciences, Tehran, Iran Majid KHANMOHAMMADI Department of Laboratory Sciences, Marand Branch, Islamic Azad University, Marand, Iran Lame AKHLAGHI Department of Parasitology and Mycology, School of Medicine, Iran University of Medical Sciences, Tehran, Iran Mahmoud MAHAMI-OSKOUEI Department of Parasitology and Mycology, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran Mehdi ARSHADI Department of Parasitology and Mycology, School of Medicine, Iran University of Medical Sciences, Tehran, Iran AND Al-Zahra Hospital, Tabriz University of Medical Sciences, Tabriz, Iran 2020 06 07 Background: Toxoplasma gondii is a protozoan parasite that belongs to the family Coccidae. We aimed to evaluate IgG avidity and the changes of anti-Toxoplasma immunoglobulins M (IgM) and G (IgG) in patients with acute leukemia and lymphoma. Methods: Ninety eight patients with Acute myeloid leukemia (AML), Acute Lymphoblastic Leukemia (ALL) and lymphoma, selected from patients referring to Imam Reza Hospital of Tabriz (38°04′N 46°18′E), in terms of the presence of anti-Toxoplasma IgM, IgG, IgG avidity antibodies and the major risk factors were evaluated. Results: The results of pre-chemotherapy evaluation showed that of the examined patients, only two cases, one patient with ALL and another patient with lymphoma, had a positive IgM titer. Overall, 46 cases had positive IgG titers, including 20 patients with AML, 15 patients with ALL and 11 patients with lymphoma. Three (3.06%) patients were positive for anti-T. gondii IgM and one of them was with new infection of toxoplasmosis in lymphoma patients. The post-chemotherapy IgG titer evaluation showed 46 [46.9% (95% CI 37.4–56.7)] positive IgG cases that this result was similar to the result of pre-treatment phase. One [1% (95% CI 0.2–5.6)] positive IgG avidity case was detected using ELISA method, in a patient with lymphoma whose IgM was also positive. There was no significant difference between the type of leukemia and the history of contact with cat. Conclusion: Performing specialized tests to diagnose toxoplasma infection before starting treatment, in immunodeficiency patients who undergo chemotherapy, is necessary; therefore, these tests should be considered in therapeutic protocols. https://ijpa.tums.ac.ir/index.php/ijpa/article/view/2939 https://ijpa.tums.ac.ir/index.php/ijpa/article/download/2939/1030