A hallmark of T. gondii infections is passage of parasites across restrictive biological barriers—intestine, blood-brain barrier, blood-retina barrier and placenta—during primary infection or reactivation of chronic disease. Traversal of cellular barriers permits rapid dissemination of parasites to gain access to biologically restricted organs. This process involves active parasite motility and tighdy regulated interactions between host cell receptors and parasite adhesins that facilitate paracellular transfer. Mounting evidence also suggests that parasites use migrating leukocytes as Trojan horses to disseminate in the organism while avoiding immune attack. Thus, the interaction of Toxoplasma with biological barriers is a determinant factor of human toxoplasmosis. The elucidation of determinants involved in the process of migration may reveal virulence factors and novel therapeutic targets to combat disease.
