Study of Tissue Orientation and Parasite Load in Various Tissues and Blood in an Experimental Mouse Model of Acute Toxoplasmosis

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.