Presentation by scanning electron microscopy of the life cycle of microsporidia of the genus Encephalitozoon

This paper presents, for the first time, documentation by detailed scanning electron microscopy of the life cycle of microsporidia of the genus Enceph alitozoon. Phase 1 is represented by the extracellular phase with mature sp ores liberated by the rupture of host cells. To infect new cells the spores have to discharge their polar filament. Spores with everted tubes show tha t these are helically coiled. When the polar tubules have started to penetr ate into a host cell they are incomplete in length. The infection of a host cell can also be initiated by a phagocytic process of the extruded polar f ilament into an invagination channel of the host cell membrane. After the p enetration process, the tube length is completed by polar tube protein whic h passes through the tube in the shape of swellings. A completely discharge d polar tube with its tip is also shown. The end of a polar tube is normall y hidden in the cytoplasm of the host cell. After completion of the tube le ngth the transfer of the sporoplasm occurs and phase 2 starts. Phase 2 is t he proliferative phase, or merogony, with the intracellular development of the parasite that cannot be documented by scanning electron microscopy. The subsequent intracellular phase 3, or sporogony, starts when the meronts tr ansform into sporonts, documented as chain-like structures which subdivide into sporoblasts. The sporoblasts finally transform directly into spores wh ich can be seen in their host cell, forming bubble-like swellings in the ce ll surface. (C) 2000 Editions scientifiques et medicales Elsevier SAS.