Manual of basic techniques for a health laboratory - libdoc.who.int

4. Parasitology 113Fig. 4.13 Invasive form of Entamoebahistolytica trophozoiteFig. 4.14 Non-invasive form ofEntamoeba histolyticatrophozoiteIdentification of motile forms of amoebaeEntamoeba histolytica (Figs 4.13 and 4.14)(dysentery amoeba)Size: 12–35mm (usually the size of 3–4 erythrocytes).Shape: when moving, elongated and changing; when not moving, round.Motility: moves in one direction; a pseudopodium pushes forward and the endoplasmflows quite rapidly into it.Cytoplasm: the ectoplasm is transparent, quite different from the fine granular textureof the endoplasm (greyish with yellowish-green streaks), which may containvacuoles.Nucleus: not visible in the motile form, but when stained with iodine solution clearlyseen to have a regular membrane and a small dense central karyosome (a blackdot).Two motile forms of E. histolytica can be found in liquid or diarrhoeal faeces: aninvasive form and a non-invasive form.Invasive form (see Fig. 4.13)The invasive form measures 20–35mm. It has vacuoles containing more or lessdigested erythrocytes (1–20 of different sizes) indicating haematophagous (bloodeating)activity and so pathogenic capability.Non-invasive form (see Fig. 4.14)The non-invasive form measures 12–20mm. It thrives in the intestinalcavity where it eats bacteria or other material that can be seen insidethe vacuoles. It is non-pathogenic.Entamoeba coli (Fig. 4.15)Size: 20–40mm (usually bigger than E. histolytica).Shape: oval or elongated, rather irregular, often non-motile or movingvery slowly, putting out blunt pseudopodia in all directions.Cytoplasm: both the ectoplasm and the endoplasm are granular anddifficult to differentiate.Inclusion bodies: numerous and varied (bacteria, yeast cells, celldebris), but never erythrocytes.Fig. 4.15 Entamoeba coli trophozoite