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Fine structure of Leishmania donovani in bone marrow aspirates from a patient with visceral leishmaniasis before and during treatment with sodium stibogluconate.

The fine structure of Leishmania donovani amastigotes has been studied in bone marrow aspirates from a 4-year-old girl with visceral leishmaniasis before and during treatment with sodium stibogluconate. Free amastigotes in the bone marrow were forming junctions with previously undescribed cytoplasmic buddings of macrophages prior to engulfment; these buddings were suggested to be transient parasitophorous vacuoles. Three stages of infection within macrophage parasitophorous vacuoles were identified: early stage in which the vacuole membrane was closely apposed to entire surface of the amastigote; advanced stage in which the vacuole became slightly distended and contained single amastigote; the late stage in which the vacuole was greatly distended and was occupied by several amastigotes. Prior to treatment, degeneration of parasites has appeared as a partial loss of the pellicle and a low dense perinuclear space and seems to be under digestive lysosomal effects of the host cell. The most consistent effects of treatment on the amastigotes were a reduction on average size and moderate increase in the electron-density of the cytoplasm which was associated with a greater concentration of ribosomes. This may occur in addition to degeneration seen before treatment which dramatically increased during treatment. It is suggested that the parasite, during treatment, is under double actions; the drug may function to lyse the parasite intracellularly, while the macrophage lysosomes act to digest the membrane of the parasitophorous vacuole and its vacuolar contents extracellularly.