Amastigote—trypomastigote differentiation
After successive amastigote divisions, these cells begin a differentiation process into trypomastigotes, the infective stage for vertebrate and invertebrate hosts, first going through an intermediary stage like epimastigotes28 (Fig. 16.4H). The crucial stimulus that triggers the amastigote to the trypomastigote transformation process, which is not synchronous, is not clear. When the cell becomes filled with trypomas- tigotes, the plasma membrane ruptures and significant degenerative processes can be observed, probably due to the intense movement of the parasites24 that are released outside the host cell (Fig. 16.4J).
Amastigote stages are also infective in vitro and in vivo. In laboratory conditions, it is possible to infect different lineages and cell types as well as laboratory animals with amastigote forms of T. cruzi2 Moreover, the transmission of Chagas disease with transplants is an additional clear evidence of this possibility of infec- tion.30 The interaction of trypomastigotes with the host cells as well as the amasti- gote stages on the cytoplasm are illustrated in Fig. 16.5.
Figure 16.5 Scanning electron micrograph showing Trypanosoma cruzi trypomastigotes (black arrows) and extracellular amastigotes (curved black arrow) invading Vero cells. Open downward arrows show surface protrusions compatible in size with internalized amastigotes. Bar = 5 pm31.
