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

122 Manual of basic techniques for a health laboratoryFig. 4.33 Types of coccidiaa: Containing four sporozoites and occasionally a few large granules clusteredat one pole; b: containing one large round granular cell; c: containing refractivegranules completely filling the interior.Coccidia (Fig. 4.33)Coccidia are protozoa that may be parasites of humans (without causing any significantpathogenic effects) or may be found in transit in the stools of people whohave consumed infected food (fish, rabbit, etc.). They appear in the stools in a formresembling cysts (and are called oocysts or sporocysts).Size: 15–20mm, depending on the species.Shape: an elongated oval, sometimes tapered at one pole.Colour: colourless and transparent (or occasionally pale yellow).Shell: a quite distinct, slightly shiny double line; sometimes an operculum is presentat one pole.There are three types of coccidia (see Fig. 4.33):(a) containing four sporozoites (small banana-shaped rods), each with a small roundnucleus; sometimes a few large granules are clustered at one pole;(b) containing one large round granular cell;(c) containing shiny granules completely filling the interior.Microscopic examination of cystsPreparation in saline wet mountCysts can be seen as transparent shiny globules standing out clearly against a greybackground. They have well-defined shells.Using the ¥ 40 objective, look for shiny round objects with a diameter roughly equalto 1–3 erythrocytes.Chromatoid bodiesLook also for chromatoid bodies (rod-shaped structures). Chromatoid bodies aremore distinct in saline mounts than in iodine mounts. These bodies are characteristicin appearance and occur in cysts of Entamoeba histolytica and E. coli. The rodshapedchromatoid bodies of E. histolytica have blunt rounded ends; those of E. colihave pointed ends. These chromatoid bodies are seen less frequently in cysts ofE. coli than in those of E. histolytica.NucleiNuclei are not easily visible in saline mounts but are clearly seen in iodine mounts.The appearance of the nucleus is important in differentiating between species ofamoeba. Therefore, if cysts (or cyst-like bodies) are seen in the saline mount, examinean iodine mount.