Faecal flotation with centrifugation
Aims: Qualitative analysis of a faecal sample for the detection of gastrointestinal parasites. In companion animals, common parasitic findings of concern include eggs of nematodes (e.g., Ascarididae, Ancylostomatidae, Trichuridae, & Capillariidae), cestodes (e.g., Dipylidium caninum, Taeniidae), oocysts of coccidia (e.g., Cystoisospora spp., Toxoplasma gondii (cats only), & Sarcocystis spp.), and other protozoa (e.g., cysts of Giardia duodenalis).
Meterials:
- Faecal sample
- Flotation solution (Zinc Sulphate m.s. 1200)
- 2 100 mL cups (e.g., paper cup, plastic cup)
- 1 round bottom tube (to use as a pestle) (a wooden tongue depressor may be substituted)
- 1 piece of gauze 20x20 cm (two layers of cheesecloth may also be used)
- Centrifuge tube
- 1 laboratory centrifuge (swinging-bucket style)
- Pasteur/transfer pipettes
- Lugol’s solution
- Glass microscope slides and coverslips
Procedure:
Place approximately 2-3 g of faeces into one of the two cups, then add 10 mL of the chosen floatation solution. Using a rounded bottom tube or tongue depressor, homogenize the mixture until the sample has been completely thoroughly broken down and mixed into the solution. Fold the piece of gauze in half two times (to create a total of 4 layers) or use 2 layers of cheesecloth and place on top of the second cup. Pour the solution through the gauze/cheesecloth to filter out the larger debris. Discard the gauze and leftover faecal material. Continually agitate the filtered suspension while collecting approximately 2 mL using a Pasteur/transfer pipette and deposit into a centrifuge tube. Continue to fill the tube with the floatation solution until a slight positive meniscus has formed. Firmly place a 24x24 mm coverslip onto the top of the test tube and centrifuge the sample for 10 minutes at 2,000 rpm. After centrifugation, carefully remove the coverslip and place it directly onto a microscope slide. Scan the entirety of the slide using a compound light microscope. To facilitate the identification of Giardia duodenalis cysts, add 1 drop of Lugol’s solution underneath the coverslip.
*If a swinging bucket centrifuge is not available, a fixed angle centrifuge may be used. Simply leave the centrifuge tube slightly under filled when centrifuging then place the tube in a rack and fill with the floatation solution until the positive meniscus is formed. Place a coverslip on top and allow it to sit for 10-15 minutes before placing on a slide and examining.
*If a centrifuge is not available, a passive floatation may be performed. This involves allowing the sample to sit in the tube after the positive meniscus has been formed for 20-30 minutes before placing a coverslip on and examining the sample. This method is less sensitive, and centrifugation is recommended, if available.
Results:
Examine the slide under the microscope, first scanning at a lower magnification (10X objective) to identify larger nematode, trematode, and cestode eggs. Higher magnifications (20X and 40X) are used to identify smaller organisms, such as protozoan oocysts and cysts (as in the case of Giardia duodenalis and Toxoplasma gondii).
References:
Flotation Technique: Zajac, A.M., Johnson, J., King, S.E. (2002) Evaluation of the importance of centrifugation as a component of zinc sulfate fecal flotation examinations. Journal of the American Animal Hospital Association, 38 (3), pp. 221-224. DOI: 10.5326/0380221
Dryden, M.W., Herrin, B.H., Payne, P.A., et al. Further Comparison of Centrifugation Versus Passive Fecal Flotation for the Recovery of Toxocara canis, Trichuris vulpis and Ancylostoma caninum Eggs. The International Journal of Applied Research in Veterinary Medicine, 18 (1), pp. 69-77.
Parasitic elements: Genchi M, Traldi G, Genchi C. (2010) Manuale di Parassitologia Veterinaria. Casa Editrice Ambrosiana. 256 pp