Arch Clin Infect Dis. 2018 October; 13(5):e13744. Published online 2018 January 29. doi: 10.5812/archcid.13744. Research Article Study of Tissue Orientation and Parasite Load in Various Tissues and Blood in an Experimental Mouse Model of Acute Toxoplasmosis Sina Sekandarpour 1, 2 , Hadi Mirahmadi 1, 2, * , Mahdi Mohammadi 3, 4 , Jalal Zaman 5 , Ramin Saravani 6, 7 and Mohammad Mousavi 2 1 Infectious Diseases and Tropical Medicine Research Center, Tubercluosis Institute, Zahedan University of Medical Sciences, Zahedan, IR Iran 2 Department of Parasitology and Mycology, Faculty of Medicine, Zahedan University of Medical Sciences, Zahedan, IR Iran 3 Health Promotion Research Center, Zahedan University of Medical Sciences, Zahedan, Iran 4 Department of Biostatistics and Epidemiology, School of Health, Zahedan University of Medical Sciences, Zahedan, IR Iran 5 Orumiyeh Military Hospital, Health Administration of Army (NEZAJA), Tehran, Iran 6 Cellular and Molecular Research Center, Zahedan University of Medical Sciences, Zahedan, IR Iran 7 Department of Clinical Biochemistry, School of Medicine, Zahedan University of Medical Sciences, Zahedan, IR Iran * Corresponding author: Hadi Mirahmadi, Infectious Diseases and Tropical Medicine Research Center, Zahedan University of Medical Sciences, Zahedan, IR Iran. Tel: +98-9149664568, Fax: +9854333442481, E-mail: hmirahmadi59@gmail.com Received 2016 September 24; Revised 2017 May 20; Accepted 2017 September 19. Abstract Background: Toxoplasma gondii is an obligate intracellular parasite, which can be found in different cells of humans and animals and infect many tissues. The virulence of T. gondii strains is commonly detected, based on the outcomes of infection in mice. The present study was performed to determine the parasite distribution and tissue tropism of tachyzoites of T. gondii RH strain in an experimental mouse model of infection, using quantitative polymerase chain reaction (qPCR). Methods: In this experiment, male and female BALB/c mice were infected through intraperitoneal injection of 103 tachyzoites of T. gondii RH strain. The assessments were performed at 1, 2, 3, 4, and 5 days postinoculation (dpi), as well as the time of death; the mice were monitored 3 times a day. After the animals were sacrificed in each group, different tissues were collected from the heart, liver, lung, muscle, kidneys, genitals, spleen, brain, eyes, and blood and maintained at -20°C. Then, DNA samples were extracted using kits, and DNA copy number was measured via qPCR, targeting B1 gene. Results: The parasite was distributed in various tissues on the first day after infection and exhibited the ability to cross the blood- brain barrier within the brain. Twenty-four hours after tachyzoite inoculation, the highest parasite load was observed in the liver tissues of both groups. Conclusions: Considering the blood flow to all tissues and transmission of parasite to other tissues, the highest parasite count was reported in the present study. These findings are invaluable for assessing the impact of new drugs on these parasites. There is also the possibility of sexual transmission, causing a significant parasite load in the genitals. Keywords: Real-Time PCR, In Vivo, Parasite Burdens, Toxoplasma gondii 1. Background Toxoplasma gondii is a protozoan member of the phy- lum Apicomplexa, which can cause severe infection in warm-blooded animals, such as humans and animals (1). Considering the global infection and spread of this parasite, it is recognized as one of the largest public health problems in one-third of the world’s population. It is mostly transmitted through consumption of under- cooked or raw meat, containing tissue cysts or oocysts ex- creted from the definitive host (2, 3). Sporozoites can in- fluence the digestive tract and are released when reaching the bloodstream (4). T. gondii can live and reproduce in a va- riety of host tissues, such as the heart, liver, kidneys, skele- tal muscles, eyes, central nervous system, and immune sys- tem cells (1, 5). Toxoplasmosis is a self-limited disease in people with a healthy immune system. However, in people with immun- odeficiency, severe clinical symptoms may appear, leading to the death of patients in some cases (6, 7). T. gondii par- asite can infect most tissues, although clinical symptoms are variable, depending on the site of infection. Therefore, severity of symptoms and pathological lesions is associ- ated with congestion and tachyzoites in different tissues (8). Most studies on parasite burden have focused on mouse models of toxoplasmosis, using microscopic obser- Copyright © 2017, Archives of Clinical Infectious Diseases. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (http://creativecommons.org/licenses/by-nc/4.0/) which permits copy and redistribute the material just in noncommercial usages, provided the original work is properly cited.