Medical Definition of amastigote
: the nonmotile, parasitic form in the life cycle of some protozoans (family Trypanosomatidae, and especially genus Leishmania) that usually develops in the cells of vertebrate hosts and occurs as a minute, ovoid or spherical body with a prominent, rod-shaped kinetoplast and a rudimentary, internal flagellum arising from a basal body For all species of Leishmania, the portion of the life cycle spent in mammalian hosts is paradoxical in that the amastigote infects macrophages, the very cells of the mammalian host that constitute its primary defense against invasion by foreign organisms.—Burton J. Bogitsh et al., Human Parasitology, 2005 In the sandfly gut the amastigotes leave the host cell, transform into promastigotes, and replicate extracellularly.—David J. Wyler and Anthony R. Mattia, The New England Journal of Medicine, 17 Mar. 1994
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