Size and shape index

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Cytoplasmic dots The dots of different species represent parasite proteins that modify red cell function in a range of ways to support parasite development, immun evasion or virulence. Their precise functions are ill defined, but their appearances have value in distinguishing the different species of parasite. The dots require a well-stained specimen to be easily seen! Schüffner's dots (P.vivax) and James' dots) (P.ovale) become apparent during the early trophzoite as faint dots then to be easily seen in later stages. These two forms of dots are morphologically indistinguishable as frequent evenly-distrubuted round dots od similar size. Maurer's dots and clefts (P.falciparum) are blue/purple coloured and are not acquired until the late trophozoite stage of parasite development. They are less consistently "dot-like" and may appear as dots, clefts or plaques. Sinton and Mulligan's stippling (P.knowlesi) may appear similar. Ziemann's stippling (P.malariae) Is not usully seen, but when present appears as faint fine (and inconspicuous) dots in cytoplasm of some ifected erythrocytes. Red cell size and shape During parasite development, each species alters the red cell that they occupy. These changes differ between species causing characteristic changes to.red. cell size and red cell shape. These changes occur from a relatively early stage of parasite development although the very earliest trophozoites may yet show these features 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. RED CELLS WITH UNCHANGED SIZE AND SHAPE Size and shape of red cells tends to be unchanged in trphozoites of P.falciparum and P.knowlesi.although in P.falciparum red cells may become crenated A B B 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. ENLARGED AND DISTORTED RED CELLS 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. P.vivax 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 Early and trophozoites of P.vivax. The increased size and red cell distortion increase as the parasites mature. In this case 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 there is no fimbriation).