Ultrastructure of excystment of Toxoplasma gondii oocysts

The excystation of sporozoites from intact Toxoplasma gondii oocysts or mechanically released sporocysts was studied by light and electron microscopy. Both intact oocysts and free sporocysts excysted in 5% bovine bile in 0.9% NaCl solution after 30-60 min incubation at 37C. Sporozoites were first activated in either intact sporocysts or oocysts within 2-12 min of incubation in bile. Sporozoites escaped from sporocysts through 4 plate-like sutures in the sporocyst wall, and from the oocyst as the oocyst wall ruptured at one or more points.