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

180 Manual of basic techniques for a health laboratoryTable 4.12 Identification of Plasmodium spp. infective to humans in blood filmsP. falciparum P. malariaeYoungtrophozoite(Stage frequently found)Cytoplasm: small, fine, pale blue ringChromatin: one or two small red dots(Stage frequently found)Cytoplasm: thick, dense, blue ringwith some granules of black pigmentChromatin: one large red dotMaturetrophozoite(Stage frequently found)Cytoplasm: rather thin, blue ring, orshaped like a comma or anexclamation markChromatin: one or two mediumsizedred dots(Stage frequently found)Cytoplasm: either (a) round, compact,dark blue, with many black particlesof pigment, or (b) in band form (inthin films only)Chromatin: a round dot or red bandSchizont(Very rare)Hardly ever found in blood films(except in very serious cases)Merozoites: 18–32Pigment: dark brownish-black(Fairly frequently found)Merozoites: 8–10 large red granulessurrounded by pale cytoplasm andarranged irregularly (young form) orin a rosettePigment: always seenGametocyte(Fairly frequently found)Shape: similar to a banana or sickleColour: pale blue (male) or dense blue(female)Nucleus: reddish-pinkPigment: a few blue–black granules inthe centre of the cytoplasm orscattered through it(Fairly frequently found)Shape: large, oval or roundedColour: pale blue (male) or denseblue (female)Nucleus: one round spot of redchromatin against one edgePigment: large black granules in thecytoplasmErythrocytesParasitedensity bNormal in sizeMay show crenation cells containingmature trophozoites; often contain afew red dots, irregular in size andshapeOften very high densityNormal in size and shapeNo red dots usually seenLow densityaThe identity of P. ovale must be confirmed by examination of a thin blood film.bThe parasite density in any area depends mainly on whether the malaria is seasonal or endemic. Adults living in endemic areas often developimmunity to the disease and have a low parasite density.1. Determination of the number of parasites/ml of blood is accomplished by countingthe number of parasites in relation to a standard number of leukocytes/ml(8000). Initially, the blood film is examined for the presence of parasite speciesand their stages of development. Using two hand tally counters, one for countingleukocytes and the other for parasites, follow one of these two procedures: