Toxoplasmosis is considered as an opportunistic parasitic disease. If post-natally acquired in children or adults, it may pass unnoticed, at least with strains of European origin. However, in the wild biotopes especially in South America, Toxoplasma gondii strains display a greater genetic diversity, which correlates to higher virulence for humans, particularly along the Amazon River and its tributaries. In French Guiana, several atypical strains have been associated with severe clinical forms: ocular toxoplasmosis and acute respiratory distress syndrome both of which can result in death. Among these, the GUY008-ABE strain was responsible for an epidemic of severe disseminated toxoplasmosis in Suriname, which led to the death of one immunocompetent individual. To better understand the mechanism underlying the hypervirulence of the GUY008-ABE strain, we have tested the rat model which compared to the mouse, better reflects the immune resistance of humans to Toxoplasma infection. Here we compare the outcome of toxoplasmosis in F344 rats infected either by the GUY008-ABE strain or the type II Prugniaud strain. We show that the GUY008-ABE strain displays a higher virulence phenotype leading to the death of all infected rats observed in this study. GUY008-ABE infection was characterized by an increase of the parasite load in several organs, especially the heart and lung, and was mainly associated with severe histological changes in lungs. Moreover, correlating with its hypervirulence trait, the GUY008-ABE strain was able to form cysts in the LEW rat model otherwise known to be refractory to infection by other Toxoplasma strains. Together, these results show that the rat is a discriminating experimental model to study Toxoplasma virulence factors relevant to the pathogenesis of human infection and that the degree of virulence is linked to the Toxo1 locus.

Toxoplasmosis is a highly prevalent human disease, and virulent strains of this parasite emerge from wild biotopes. Here, we report on the potential of a histone deacetylase (HDAC) inhibitor we previously synthesized, named JF363, to act in vitro against a large panel of Toxoplasma strains, as well as against the liver and blood stages of Plasmodium parasites, the causative agents of malaria. In vivo administration of the drug significantly increases the survival of mice during the acute phase of infection by T. gondii, thus delaying its spreading. We further provide evidence of the compound’s efficiency in controlling the formation of cysts in the brain of T. gondii-infected mice. A convincing docking of the JF363 compound in the active site of the five annotated ME49 T. gondii HDACs was performed by extensive sequence–structure comparison modeling. The resulting complexes show a similar mode of binding in the five paralogous structures and a quite similar prediction of affinities in the micromolar range. Altogether, these results pave the way for further development of this compound to treat acute and chronic toxoplasmosis. It also shows promise for the future development of anti-Plasmodium therapeutic interventions.