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

4. Parasitology 111Table 4.3 Pathogenicity of intestinal protozoaSpeciesAmoebaeEntamoeba histolyticaEntamoeba coliEntamoeba hartmanni, Endolimaxnanus, Iodamoeba butschlii,Dientamoeba fragilisFlagellatesGiardia intestinalisTrichomonas hominisChilomastix mesniliCiliatesBalantidium coliPathogenicityOnly amoeba that is commonly pathogenic tohumans. May cause dysentery or abscessesNon-pathogenic, but very commonNon-pathogenic. Differentiation is difficult but notreally necessary; it is enough to be able todistinguish these species from EntamoebahistolyticaPathogenicNon-pathogenicNon-pathogenicPathogenic4.3 Intestinal protozoaProtozoa are microorganisms consisting of a single cell. Intestinal protozoa may befound in stools in their motile form (trophozoites) or as cysts. Some intestinal protozoaare pathogenic (see Table 4.3); others are harmless. All these protozoa arefound throughout the world.4.3.1 Identification of motile forms (trophozoites)The trophozoites of protozoa are motile (Fig. 4.11):— either because of slow movements of the cell (amoebae);— or because they have rapidly moving flagella (long whip-like threads) or cilia(numerous short hairs).Trophozoites are chiefly found in:— watery stools— stools containing mucus— soft formed stools.The following features are useful for the identification ofmotile forms of intestinal protozoa (Fig. 4.12):— size— cytoplasm— pseudopodia— nuclei— ectoplasm— endoplasm— vacuoles— inclusion bodies containing erythrocytes, bacteria,yeast cells, debris, etc.— nuclear membrane (chromatin)Fig. 4.11 Motile forms of protozoaA: amoeba; F: flagellate; C: ciliate.— nuclear karyosome—flagella— undulating membrane.