Toxoplasma gondii is a protozoan parasite that is the causative agent of toxoplasmosis, an infection with high prevalence worldwide. Most of the infected individuals are either asymptomatic or have mild symptoms, but T. gondii can cause severe neurologic damage and even death of the fetus when acquired during pregnancy. It is also a serious condition in immunodeficient patients. The life-cycle of T. gondii is complex, with more than one infective form and several transmission pathways. In two animated videos, we describe the main aspects of this cycle, raising questions about poorly or unknown issues of T. gondii biology. Original plates, based on electron microscope observations, are also available for teachers, students and researchers. The main goal of this review is to provide a source of learning on the fundamental aspects of T. gondii biology to students and teachers contributing for better knowledge and control on this important parasite, and unique cell model. In addition, drawings and videos point to still unclear aspects of T. gondii lytic cycle that may stimulate further studies. Graphical Abstract

The encystation process is a key step in Toxoplasma gondii life cycle, allowing the parasite to escape from the host immune system and the transmission among the hosts. A detailed characterization of the formation and structure of the cyst stage is essential for a better knowledge of toxoplasmosis. Here we isolated cysts from mice brains and analysed the cyst wall structure and cyst matrix organization using different electron microscopy techniques. Images obtained showed that the cyst wall presented a filamentous aspect, with circular openings on its surface. The filaments were organized in two layers: a compact one, facing the exterior of the whole cyst and a more loosen one, facing the matrix. Within the cyst wall, we observed tubules and a large number of vesicles. The cyst matrix presented vesicles of different sizes and tubules, which were organized in a network connecting the bradyzoites to each other and to the cyst wall. Large vesicles, with a granular material in their lumen of glycidic nature were observed. Similar vesicles were also found associated with the posterior pole of the bradyzoites and in proximity to the cyst wall.

Objectives: To study the antiproliferative effects of ER119884 and E5700, two quinuclidine-based inhibitors of squalene synthase (SQS), against Toxoplasma gondii tachyzoites in epithelial cells. Methods: The antiproliferative effects of the quinuclidine derivatives, alone or in combination with epiminolanosterol or antifolates, were analysed, resulting in the construction of isobolograms. The ultrastructure of treated tachyzoites was analysed by transmission electron microscopy. Results: The quinuclidine derivatives demonstrated selective anti-T. gondii activity, arresting parasite growth with IC₅₀ values of 0.66 and 0.23 μM for ER119884 and E5700, respectively, after 24 h of interaction and 0.44 and 0.19 μM after 48 h of interaction. Both compounds induced remarkable alterations in the parasite ultrastructure, such as mitochondrial swelling and the presence of autophagosome-like structures, after 24 h of treatment. Combination of these quinuclidine derivatives with the antifolates sulfadiazine and pyrimethamine produced a synergic effect. When epiminolanosterol was combined with E5700, the effect observed was synergic, whereas the combination with ER119884 produced no interaction. Conclusions: E5700 and ER119884 demonstrated selective activity against T. gondii tachyzoites and are a possible alternative to be used in association with the current therapy. The ultrastructural alterations observed suggest a possible interference with lipid metabolism.

The antifungal agent itraconazole is an effective drug against systemic mycoses inhibiting cytochrome P-450-mediated ergosterol synthesis, essential