The fine structure of Leucocytozoon simondi. II. Megaloschizogony

Abstract

Incompletely divided cytomeres released from hepatic schizonts of L. simondi undergo prolific development in phagocytic cells of the host which become grossly hypertrophied. These infected cells together with the parasites within are termed megaloschizonts. Young megaloschizonts contain numerous round cytomeres bounded by a five-layered envelope. With further development the cytomeres expand and become invaginated. Microtubular spindles occur in dividing parasite nuclei at this stage of development. Thickenings form on the single membrane bounding the newly formed cytomeric surfaces. Electron-dense paired organelles develop adjacent to the thickenings which become the polar rings of merozoites. Abundant granular endoplasmic reticulum and numerous mitochondria with vesicular cristae are seen in the cytoplasm of invaginated cytomeres. Nuclear division by multiple fission and further cytoplasmic fragmentation continue until uninucleate merozoites are formed. Male and female merozoites can be distinguished by the difference in the density of their cytoplasm and each contains a mitochondrion and paired organelles with the associated polar ring. The megaloschizont is surrounded by a capsule whose irregular inner surface is lined by the host plasma membrane. Outside this lies a thick filamentous zone from which numerous vesicles are pinched off and are seen within the hypertrophied host cytoplasm. A fibrous layer bounds the outer surface of the megaloschizonts.

Leucocytozoonosis

“…These various stages will be discussed further in the next section in relation to the life cycle. The ultrastructure of the various stages of L. simondi has been studied by S. S. Desser and associates (Desser 1970a(Desser -c, 1972(Desser , 1973Desser et al 1970;), and for meronts of L. toddi by Raidal and Jaensch (2000).…”

The fine structure of Leucocytozoon simondi. III. The ookinete and mature sporozoite

“…Midguts and salivary glands containing ookinetes and sporozoites respectively were removed into Haye's saline and transferred immediately into 1.25% glutaraldehyde or 1.2% KMn04 in 0.9% NaCI, and processed for electron microscopy in a manner similar to that described before (7,8). To relate observations on stages of sporogony made with the electron microscope to those made with the light microscope, smears of infected midguts and salivary glands were stained with Giemsa and examined.…”