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

4. Parasitology 115Motility: either non-motile (most often) or very motile (in very fresh fluid stools),with pseudopodia similar to the blades of an electric fan; quickly becomes nonmotileunder the coverslip.Cytoplasm: clear ectoplasm.Inclusion bodies: bacteria.Nucleus: one or two nuclei, visible after staining with iodine solution; karyosomessplit into 4–6 granules (membrane hardly visible).Identification of motile forms of flagellatesAll of these parasites, with the exception of Trichomonas hominis, can appear in anactive flagellate vegetative form or as inactive cysts.Giardia intestinalis (Fig. 4.20)Size: 10–18mm (size of two erythrocytes).Shape: rather elongatedfront view: similar to a pearside view: spoon-shaped.Motility: either moves forward in small rapid jerks in adefinite direction, sometimes turning in a loop (fluidstools), or is hardly motile.Nuclei: two large oval nuclei, faintly visible.Important:●●●The characteristic movement is seen only in freshliquid stools.Flakes of mucus in fluid stools often contain clustersof large numbers of G. intestinalis.The vegetative and cystic forms of G. intestinalis areoften found together in soft stools.Trichomonas hominis (Fig. 4.21)Size: 10–15mm (slightly smaller than G. intestinalis).Shape: oval with two pointed poles.Motility: whirls and turns in all directions, seeming tovibrate.Undulating membrane: present on one side only;extremely motile (a rapid wavy movement).Fig. 4.20 Giardia intestinalis trophozoiteNucleus: one nucleus, difficult to see.Flagella: usually four.T. hominis is the most resistant flagellate. It remains motile even in old stools.Chilomastix mesnili (Fig. 4.22)Size: 10–15mm.Shape: triangular and tapered at one end, appears twisted.Motility: moves in one definite direction, in a spiral.