Pathogenesis
    Toxoplasma gondii is an obligate intracellular protozoan existing in three forms: the oocyst, the tachyzoite and the bradyzoite. Replication of the parasite takes place in the intestine of the cat family Felidae, as a result the production of oocysts. Millions of oocysts are shed into the feces of cats. After sporulation, oocysts containing sporozoites are infective when ingested by mammals, including humans. At this point the tachyzoite stage starts. The rapidly dividing form of the parasite is represented by the stage of tachyzoites. Active penetration is the way that the parasite contaminates all the nucleated cells. After that, a continuous proliferation leads to host cells destruction and tachyzoites invade and damage adjacent cells (2).   Furthermore, they are disseminated via bloodstream and infect many tissues. This situation causes a strong inflammatory response, tissue damage and, therefore clinical manifestations. The host’s immune response can put pressure and limit the growth of tachyzoites, and so they are transformed into bradyzoites, which they form tissue cysts (in the brain and skeletal and heart muscles). Bradyzoites stay inside cysts for the entire life of the host and although they are morphologically identical to tachyzoites, multiply slowly. In immunocompromised patients (patients with AIDS, organ transplantation, cancer, or taking immunosuppressants), bradyzoites can be released from cysts and transform back into tachyzoites (1). In addition, tissue cysts are considered to be infective stages for intermediate hosts (2).