Amastigote

A stage in the life cycle of certain parasitic protozoa

Amastigote
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The amastigote is a stage in the life cycle of certain parasitic protozoa, particularly those belonging to the order Kinetoplastida, such as the genera Leishmania and Trypanosoma. Amastigotes are characterized by their small, round or oval shape and the absence of a flagellum, which distinguishes them from the promastigote and trypomastigote stages that possess flagella.

Life Cycle

Amastigotes are typically found within the host cells of mammals, where they multiply by binary fission. In the case of Leishmania species, amastigotes reside within macrophages, a type of immune cell. The transformation from promastigote to amastigote occurs after the parasite is phagocytosed by the macrophage. The acidic environment of the phagolysosome triggers the transformation into the amastigote form, which is adapted to survive and replicate within this intracellular environment.

In Trypanosoma cruzi, the causative agent of Chagas disease, amastigotes are found in the cytoplasm of various host cells, including muscle and nerve cells. They transform from the trypomastigote form after the parasite invades the host cell.

Morphology

Amastigotes are typically 2-4 micrometers in diameter. They have a nucleus and a kinetoplast, which is a unique structure containing a network of circular DNA. The kinetoplast is a defining feature of the Kinetoplastida order. Unlike other stages, amastigotes lack an external flagellum, which is why they are sometimes referred to as "non-flagellated" forms.

Pathogenesis

The presence of amastigotes within host cells is associated with the pathology of diseases such as leishmaniasis and Chagas disease. In leishmaniasis, the destruction of macrophages and the subsequent immune response lead to the characteristic lesions of the disease. In Chagas disease, the destruction of infected cells, particularly in the heart and digestive tract, leads to the chronic symptoms associated with the disease.

Diagnosis

The identification of amastigotes in clinical samples is crucial for the diagnosis of diseases like leishmaniasis and Chagas disease. In leishmaniasis, amastigotes can be observed in tissue biopsies or aspirates stained with Giemsa stain. In Chagas disease, amastigotes may be detected in tissue samples from affected organs.

Also see

• Leishmaniasis
• Chagas disease
• Kinetoplastida
• Promastigote
• Trypomastigote