Page 151 - The Veterinary Laboratory and Field Manual 3rd Edition

120 Susan C. Cork and Mani Lejeune

both and divide by two to get the average This technique may not pick up all eggs,
number. therefore to ensure detection where there are
3 Allow the slide to stand for 3–4 min and then only a few eggs in a sample a more sensitive
count all the eggs under the ruled square. technique such as the differential centrifugal
4 The total number of eggs counted × 100 indi- flotation technique is recommended.
cates the number of eggs per gram of faeces.
ModIFIEd StoLL countInG tEcHnIquE
(Calculation: This depends on the volume of (SEdIMEntatIon)
the counting chamber under the grid [usually Use a calibrated pipette or pre-determine the
0.15 ml for the McMaster slide]. If in doubt, volume of a number of drops from a vertically
check with the manufacturer of the slide used.) held Pasteur pipette (usually about 0.03 ml/
If there was 3.0 g of faeces in 45.0 ml of the drop). Calibration can be done by weighing the
standard suspension, then in 0.15 ml there drops. Once this has been done the pipette can
is 0.01 g of faeces. Thus the number of eggs be used for several counts.
in 0.01 g × 100 = the total number of eggs in
1.0 g of faeces. The faecal egg count = eggs per 1 Prepare a standard suspension (as outlined
gram of faeces so if there were an average 4 eggs previously), with water as the suspension fluid.
counted under each grid of the McMaster slide 2 Thoroughly mix the standard suspension and
then this × 100 = 400 eggs per gram (EPG). fill the pipette, place two to three pools of

Figure 3.5 Filling the chambers
on a McMaster slide (A) for a
worm egg count (see text). A fine
tipped pipette (B) is used to fill the
counting chamber(s) of the slide
(C) with faecal suspension. The
McMaster slide is then viewed
under the microscope. Parasite
eggs will float to the surface of the
grid. When counting the eggs in a
grid it is convention to include eggs
which touch the line on the left and
top sides but not eggs which lie
on the lines at the right or bottom
sides.

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