[Retarded schizogony of Plasmodium yoelii yoelii in rodents treated with ethionine or subjected to a methionine deficiency: histological and ultrastructural studies].

Histological and ultrastructural aspects of acute and chronic pre-erythrocytic schizonts of P. yoelii yoelii were studied with: a) acute schizonts in normal rodents; b) chronic schizonts induced in rodents receiving ethionine injections or on a low methionine diet; Experimentally induced chronic schizonts frequently have the same histological aspect as those observed in wild Thamnomys from Africa. The ultrastructural evolution of the vacuole system described by Seureau et al. in acute schizonts is discussed; new evidence is presented to support the hypothesis according to which the contents of the vacuoles are enzymatic in nature. Ultrastructural studies of chronic schizonts show alterations in the sites of synthesis (zones of rough endoplasmic reticulum small and not numerous, absent in the most delayed schizonts; vesicle system poorly developed and also disturbances of nuclear development (slow division, apparently inhibited in the most retarded forms.) A peripheral accumulation of vacuoles in many chronic schizonts without discharge of their contents to the parasitophorous space, might indicate an alteration of their membranes, leaving them unable to fuse with the schizont plasmalemma.