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Parasitology 119

detailed descriptions of less frequently used or
more complicated techniques can be found in recipe for Sheather’s sugar
the bibliography at the end of the chapter. solution

dIFFErEntIaL cEntrIFuGaL FLotatIon 454 g granulated sugar, 355 ml tap water,
tEcHnIquE 6 ml full-strength (37%) formaldehyde
Although saturated salt solution can be used Heat the tap water to near boiling. Add
to perform this protocol it is preferable to use the granulated sugar, and stir until the sugar
Sheather’s sugar (1.32–1.27 SpG) and ZnSO is dissolved. Allow the mixture to cool to
4
(1.18 SpG) solution simultaneously as this can room temperature, and then add the form-
help in quantitation of a whole gamut of parasite aldehyde. Check the solution’s specific
stages that could be present in a faecal sample. gravity, and adjust it to 1.27 by adding water
The steps involved are outlined below: or sugar.
Source: Blagburn, B.L., Butler, J.M. (2006) Optimize
1 Prepare a faecal suspension as indicated pre- intestinal parasite detection with centrifugal fecal
viously. flotation. Veterinary Medicine 101(7): 455–464.
2 After discarding/decanting the supernatant,
place the tube(s) in a test tube rack and re-
suspend the sediment in a small volume of parasite stages counted during microscopic
flotation solution by mixing thoroughly. examination is easily expressed as number of
Advisable to process two tubes of same faeces eggs present per gram of faeces.
simultaneously, one with Sheather’s sugar These calculations allow for the fact that
(see box) and the other with ZnSO solution. some eggs will not be recovered on the cover
4
3 Gently top up with flotation solution to form slip. There is considerable error in many of the
a small convex meniscus at the top of the standard counting techniques but the results
tube. are adequate for clinical diagnostic purposes.
4 Carefully lower a cover slip(s) vertically For greater accuracy repeating the procedure for
onto the top of the tube(s). Avoid trapping each sample is advised (that is, run duplicates).
large air bubbles. Leave to stand for 15–20
minutes. Alternatively, centrifuge at a slow ModIFIEd McMaStEr countInG tEcHnIquE
2
speed (1000–1500 rpm) for 15 min. (FLotatIon)
5 Vertically lift the cover slip off the tube(s), See Figures 3.5 and 3.6 for an illustration of the
together with the fluid adhering to it and required equipment and procedure.
place it on a microscope slide.
6 Examine under the medium (10×) or high 1 Complete steps 1–7 (as described previously)
(20×) power of a microscope and count all and re-suspend the deposit in saturated salt
parasite stages on the slide. Lungworm larvae (NaCl) solution or Sheather’s sugar in the
and Giardia sp. cysts are counted in ZnSO same volume (that is, 15 ml).
4
float, whereas the rest of all are counted in 2 Mix the sample and then remove a small
sugar float. volume of fluid from the saturated salt sus-
pension and fill the counting chamber of a
Calculation: If the faecal suspension is prepared ruled McMaster slide (usually calibrated
as described previously, 1 g of faecal sample to hold 0.15 ml). For the greatest accuracy
would be present in each tube. Therefore, fill two chambers and count the eggs in

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