SOP â Malaria Microscopy - NVBDCP

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8.3.7 ResultsQuality Assurance of Malaria Diagnostic testsWhile examining thick and thin smears, along with the malaria parasite, normal componentsof the blood is also seen as described at 3. 7.4.8.3.7.1 Malaria parasitesMalaria parasites take up stain in a special way in both thick and thin blood films thatenables to distinguish the various parts of the parasite. They pass through a number ofdevelopmental stages, However, in all stages, the same parts of the parasite will stain thesame colour.• Chromatin (part of the parasite nucleus) is usually round in shape and stainsdeep red.• Cytoplasm occurs in a number of forms, from a ring shape to a totallyirregular shape. It always stains blue, although the shade of blue may varybetween the malaria species.8.3.7.1.1 Stages of the malaria parasiteStages of the malaria parasite that are seen in peripheral blood films are described below:Trophozoite stageThis stage is most commonly seen; it is often called the ring stage, as it mostly takes theform of an incomplete ring. The trophozoite stage is a growing stage, the parasite within thered blood cell may vary in size from small to quite large. Pigment appears as the parasitegrows. Malaria pigment is a by-product of the growth or metabolism of the parasite. It doesnot stain but has a colour of its own, which may range from pale yellow to dark brown orblack.Schizont stageDuring the schizont stage the malaria parasite starts to reproduce. This reproduction isreferred to as asexual because the parasite is neither male nor female but reproduces itselfby simple division. There are several obvious phases in this stage, ranging from parasiteswith two chromatin pieces to parasites with a number of chromatin dots and definitecytoplasm.Gametocyte stageThe gametocyte is the sexual stage in which the parasites become either male or female inpreparation for the next stage, the extrinsic phase which takes place in the stomach of thefemale anopheline mosquito. Gametocytes may be either round or banana-shaped,depending on the species. The way in which the parasite takes up the stain also helps toidentify male (microgametocyte) or female (macrogametocyte). Some stages of the malariaparasite are shown in Figure 5.SOP – Malaria Microscopy© Copyright to Dte. NVBDCP Only. Any modification are prohibited
Quality Assurance of Malaria Diagnostic testsFig. 5 – Various stages of malaria parasiteRing stage (Pf)Schizont stage Gametocyte stage(Pv)(Pf)(Photo source: RMRC, ICMR, Diburgarh)8.3.7.1.2 Species of malaria parasiteThe effect of the parasite on red blood cells is also important because it helps to identify themalaria species. There are four species of malaria parasites that affect humans:1. P.vivax is the commonest species in India. It is the largest of the malariaparasites found in humans.2. Plasmodium falciparum, which is also the common species in India andresponsible for conditions like cerebral malaria and even death.3. P.malariae is a less common species in India, prevalant in some parts ofOrissa, Madhya Pradesh and Chhattisgarh.4. P.ovale is not prevalent in India but reported from many countries, especiallyfrom Africa.8.3.7.2 Appearance of parasite species in thin blood filmsThe simplest guide to distinguish between the four species of malaria is the effect theparasite has on infected red blood cells. Features to concentrate on include the size of thered blood cell (whether it is enlarged or not) and whether or not staining reveals Schuffner’sdots or Maurer’s dots (also known as Maurer’s clefts) within the cell as shown in the Figure6.Fig. 6 - P. falciparum and P. vivax as seen in the thin smears(Photo source WHO)SOP – Malaria Microscopy© Copyright to Dte. NVBDCP Only. Any modification are prohibited
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SOP â Malaria Microscopy - NVBDCP