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

4. Parasitology 167Method1. Collect 4ml of venous blood. Expel into a bottle containing 1ml of trisodiumcitrate solution. Mix.2. Measure into a conical centrifuge tube 10ml of 2% formaldehyde solution. Add1ml of citrated blood. Mix. Wait 5 minutes for the erythrocytes to lyse.3. Centrifuge for 5 minutes at 10000g. Pour off the supernatant fluid. Tap the tubeto mix the deposit.4. Place one drop of the deposit on a slide. Spread the drop to form a thin smearand leave to air-dry.5. Fix the smear using a 1:1 mixture of ethanol and ether. Leave to dry for 2 minutes,then stain immediately as described on page 170 to identify the species ofmicrofilaria.Alternative method using a microhaematocrit centrifuge1. Collect 4ml of venous blood. Expel into a bottle containing 1ml of trisodiumcitrate solution. Mix.2. Three-quarters fill a microhaematocrit capillary tube with the citrated blood.Seal one end of the tube with plastic modelling clay or by heating.3. Centrifuge in a microhaematocrit centrifuge at 10000g for 2 minutes.4. Lay the capillary tube on a slide and secure the two ends with adhesive tape.5. Examine the dividing line between the blood cells and the plasma under themicroscope (Fig. 4.123), using the ¥ 10 objective with the condenser aperturereduced.Motile microfilariae will be seen at the bottom of the column of plasma, just abovethe layer of leukocytes and erythrocytes (Fig. 4.124).The tube can be snapped at the bottom of the column of plasma (see Fig. 4.124).Use the first drop from each piece of the broken tube to prepare a thick film. Stainthe film as described on page 170 to identify the species.Capillary blood can also be examined by this method. Collect two drops of capillaryblood from the finger on to a slide and mix with one drop of 2% trisodiumcitrate solution.Fig. 4.123 Examining the microhaematocritcapillary tube under themicroscopeFig. 4.124 Motile microfilariaeE: erythrocytes; L: leukocytes;P: plasma.