The chemotherapy of rodent malaria, XXXIV. Causal prophylaxis Part III: Ultrastructural changes induced in exo-erythrocytic schizonts of Plasmodium yoelii yoelii by primaquine.

Wistar rats were injected intravenously with sporozoites from Anopheles stephensi infected with Plasmodium yoelii yoelii. The animals were subsequently treated with primaquine at doses of 30, 50 or 100 mg kg-1 at various times. Liver biopsies were made and the exoerythrocytic schizonts examined by light and electron microscopy between 45 and 50 hours. The action of the drug appeared to be principally on the parasite mitochondria, the membranes of which became thickened, then proliferated into multiple layers. Finally the whole organelles swelled up losing all structural organisation. Other parasite membranes were affected similarly and the peripheral enzyme granules disappeared. Following treatment the small, disrupted schizonts were apparently absorbed by their host cells which appeared unaffected by primaquine.