Schizont Development

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How does schizont appearance change during their development? The schizont form we see reflects successive cycles of asexual division that eventually result in the formation of multiple separate "merozoite" forms that are relaesed as the red cell breaks down. Each merozoite then goes on to infect another red cell. This is therefore a progressive process and schizonts will look very different depending on which stage of development they represent. Below are images of schizonts at different developmental stages. SMALL ROUND RED CELLS P.malariae The red cells in this species remain round and are often small in size A B The early (A) and late trophozoites (B) shown in this image each lie within round erythrocytes with reduced size. THE INITIAL ASEXUAL DEIVISION P.falciparum (and P.knowlesi) Red cell size and shape is generally unchanged although they may become crenated A B The early (A) trophozoites lie within red cells that do not change size or shape, at later development (B) they may remain unchanged or acquire subtle crenation. IMMATURE SCHIZONT APPEARANCES For both P.ovale and P.vivax the red cells become progressively enlarged and distorted as the parasites develop. It may not be possible to distingish the species based on red cell appearances, but there are differences which should be looked for. P.ovale Expect increased red cell size but this may not be marked; the typical shape is an ovoid shape (hence the name) and there may be characteristic finbriation of cytoplams (that may be limited to one pole of the cell). A B Early (A) and late (B) trophozoites o P.ovale. In each case there is a tendency for red cells to have an ovoid shape and there is distortion of the cytoplasm with sharp projectiosn (fimbriation). These orregular and spiky projections differ from the rounded crenation that may be seen in P.falciparum. MATURE SCHIZONT APPEARANCES This species tend to have the largest red cell size that becomes evident at quite and early stage; the typical shape is quite irregular fimbriation is not (generally) seen. A B Trophozoites of P.vivax cause increase in size and distortion of red cells as the parasites mature. Here, the the early trophozoite (A) is enlarged but still retains a relatively undistorted elongated shape (similar to P.ovale); however the late form (B) is has a very irregular shape (note that unlike P.ovale the red cell is not fimbriated). MEROZOITE RELEASE