amastigotes

Amastigotes are a non-flagellated intracellular life stage of certain kinetoplastid parasites, most notably Leishmania species and Trypanosoma cruzi. In the mammalian host, these forms are adapted to living inside host cells, whereas their flagellated forms reside in the insect vector or alternate environments.

Morphology and identification: Amastigotes are typically small (about 2–5 μm), ovoid or spherical, with a nucleus and a single kinetoplast. They lack a free posterior flagellum and do not form motile forms outside cells.

Habitat and replication: In Leishmania infections, amastigotes inhabit macrophages within parasitophorous vacuoles, where they replicate by binary fission. In Trypanosoma cruzi infections, amastigotes multiply in the cytoplasm of various host cells (often muscle and neuronal tissue) and later differentiate into the non-replicative, flagellated trypomastigotes that disseminate.

Clinical relevance: The presence of amastigotes in tissue is diagnostic for leishmaniasis (Leishman-Donovan bodies) and Chagas disease. Detection is typically by microscopic examination of tissue smears, bone marrow, splenic aspirates, or biopsy specimens, supported by molecular methods.

Lifecycle note: Amastigotes represent the intracellular, non-flagellated stage in mammals; transmission between hosts occurs via the insect vector or through cell-to-cell spread, depending on species.