Bovis ISSN 2398-2993

Parasitology: fecal examination techniques

Synonym(s): McMaster, sedimentation, Baermann, fecal culture, fecal egg count reduction test

Contributor(s): Mike Taylor , Andrew Forbes

Overview

  • Adult worms of gastrointestinal parasites in the intestine, and fluke infections in the stomach and liver, shed eggs into the feces, which can be detected and classified to identify or estimate patent worm infections and burdens.
  • Protozoa species shed oocysts/cysts into the feces which can be used in identify infections.
  • Adult lungworms shed first stage larvae in the feces, which can be used to confirm patent lungworm infections.

Sampling

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Tests

Methodologies

  • Flotation methods for nematode and fluke eggs and coccidia oocysts .
    • Saturated salt solution, specific gravity 1.20 at 20°C (400g NaCl in 1000 ml water).
    • ZnSO4 solution, specific gravity 1.36 (700 g ZnSO4 in 1000 ml water).
    • Sugar solution specific gravity 1.27 (500 g sucrose in 1000 ml water).
  • Sedimentation technique for fluke eggs .
  • Baermann’s technique for lungworm larvae identification Lungworm and larval culture.
  • Oocyst sporulation and identification.
Helminth eggs
  • Eggs of trichostrongyles, Ostertagia, Cooperia, Haemonchus, Trichostrongylus. Nematodirus, Strongyles, Chabertia, Oesophagostum, Bunostomum), and other gastrointestinal nematodes (Toxocara, Strongyloides, Trichuris) and sometimes tapeworm (Moniezia) eggs will be seen .
  • Fluke eggs (Fasciola, Paramphistomum Calicophoron).
Coccidia oocysts
  • Oocysts of coccidia (Eimeria).
McMaster technique
  • 3 g feces mixed with 42 ml saturated salt solution.
  • The suspension is poured through a 1 mm aperture sieve (tea strainer) and liquid squeezed out of the feces.
  • The suspension or filtrate is well mixed with a wide-mouthed pipette drawn up and used to fill the McMaster chambers .
  • The filtrate should be mixed to fill each chamber separately.
  • In a 2 chamber McMaster slide all the eggs or oocysts in both grids (volume 0.3 ml) are counted and multiplied by 50 to give eggs per gram (epg) or oocysts per gram (opg) of  feces.
Fluke eggs
  • Examination for liver fluke eggs in feces provides an indication of fluke infection but is subject to a number of limitations .
  • Eggs only appear in the feces once infections are patent (adult fluke in the bile ducts) and egg excretion from the gall bladder can be intermittent.
  • Fluke-infected cattle have low egg outputs and there are large variations between animals.
  • Sedimentation techniques are more sensitive than the McMaster technique.
  • Many laboratories do not count fluke eggs but simply report a positive or negative result according to their presence or absence.
  • Rumen fluke eggs  (Paramphistomum, Calicophoron) are similar in size to Fasciola eggs but paler in color.
Sedimentation method
  • Collect a minimum of 10 g of fresh feces from 10 randomly selected animals.
  • Samples may be examined individually, or as a composite from which sub-samples are taken.
  • Homogenize 10 g of feces with 100 ml of water in a beaker.
  • Add 2 drops of Teepol detergent to the homogenate to improve the release of eggs from fecal material.
  • Pour through a strainer and collect filtrate into beaker or collecting bowl.
  • Strain filtrate through a second screen (~250 µm aperture) into a conical flask.
  • Half fill beaker with water and wash through the screen into the conical flask.
  • Allow filtrate in conical flask to sediment for 3 min.
  • Siphon off supernatant taking care not to disturb the sediment.
  • Repeat steps 9 and 10 if necessary by adding more water to the sediment to further clean the sample.
  • Differentiation of the eggs can be enhanced by adding a couple of drops of methylene blue to the final sediment.
  • Examine sediment under microscope by pipetting a small volume onto an ordinary microscope slide with a long coverslip (40 x 22 mm) and repeating until all the sediment has been examined.
    • Alternatively, eggs can be counter in a Petri dish using a dissecting microscope.
Baermann technique for Dictyocaulus L1 and infective nematode L3
  • Dictyocaulus eggs hatch within a few hours so that identification of L1 in feces will be necessary if the feces have been held at room temperature for any time.
  • Gastrointestinal eggs will need to be cultured to L3 for generic identification.
  • Spread 10 g or more of feces on a piece of double gauze in a Baermann apparatus.
  • Stand for 6-8 h or overnight.
  • Remove the bottom 10 ml of fluid and either centrifuge or stand for a few hours and examine the sediment microscopically .
Fecal culture for nematode larvae
  • Break up a fecal sample.
  • Half-fill a jar with a loose fitting cap.
  • Incubate in the dark (retards fungal growth) at 27°C for 7 days or at room temperature for 10-20 days.
  • Recover the larvae from the feces and washings of the jar by the Baermann technique.
  • Larval differentiation is based on identification of the characteristic morphological features of the recovered third stage larvae.
Fecal Egg Count Reduction (FECR) test
  • Used to check efficacy of a given anthelmintic.
  • Ensure that animals are accurately weighed and dosed and recommended.
  • FEC performed on day of dosing and either 7 days (levamisole Levamisole), or 10-14 days later for benzimidazole and macrocyclic lactones.
  • A reduction in FEC of 90% is expected, and a reduction of much less than this suggests drug-resistant parasites may be present.

Availability

  • FECs are routinely conducted within a number of government, research and private laboratories.
  • Other parasitologicaly methods are more specialised and are normally only undertaken by specialist parasitology laboratories.

Validity

Sensitivity

  • Test sensitivity for floatation and sedimentation techniques vary depeding on the volume of feces examined and any dilution factor used in the procedure.
  • The Standard McMaster Method uses a 1 in 15 dilution, eg 3 g feces in 42 ml solution. The volume under a grid is 0.15 ml and in a chamber is 0.5 ml. The following sensitivities therefore apply:
    • 1 grid <100 epg.
    • 2 grids <50 epg.
    • 1 chamber <30 epg.
    • 2 chambers <15 epg.
  • Sensitivity can be further increased by using a 1 in 10 dilution (4.5 g feces in 40.5 ml). The sensitivities are then:
    • 1 grid <66 epg.
    • 2 grids <33 epg.
    • 1 chamber <20 epg.
    • 2 chambers <10 epg.

Specificity

  • Microscopic identification is highly specific.
  • However, it is not possible to differentiate between different species, of trichostrongyle eggs by examination of the eggs alone. Fecal culture and larval identification is usually required although PCR methods have recently been developed.

Technique (intrinsic) limitations

Numbers of eggs reflect only the presence of adult female worms and do not always indicate the number of worms present in the animal so there is no direct linear correlation between actual worm burden and the FEC.
Numbers of trematode or cestode eggs, and protozoa cysts in feces, may provide less reliable estimates of parasite burdens due to intermittent excretion.

Technician (extrinsic) limitations

Microscopic identification of some parasite stages (certain helminth eggs and protozoan cysts; and larval differentiation) is highly specific and requires a considerable amount of expertise and training.

Result Data

This article is available in full to registered subscribers

Sign up now to purchase a 30 day trial, or Login

Further Reading

Publications

Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Roeber F, Hassan E B, Skuce P, Morrison A, Claerebout E, Casaert S, Homer D R, Firestone S, Stevenson M, Smith L, & Larsen J. (2017) An automated, multiplex-tandem PCR platform for the diagnosis of gastrointestinal nematode infections in cattle: An Australian-European validation study. Veterinary Parasitology 239, 62-75 PubMed.
  • Pereckiene A, Kaziunaite V, Petkevicius S, Malakauskas A, Sarkunas M & Taylor M A (2007) A comparison of modifications of the McMaster method for the enumeration of Ascaris suum in pig faecal samples. Veterinary Parasitology 149, 111-116 PubMed.
  • Coles G C, Jackson F, Pomroy W E, Prichard R K, Samson-Himmelstjerna G, Silvestre A, Taylor M A & Vercruysse J (2006) The detection of anthelmintic resistance in nematodes of veterinary importance. Veterinary Parasitology 136, 167 – 185 PubMed.
  • van Wyk J A, Cabaret J & Michael L M  (2004) Morphological identification of nematode larvae of small ruminants and cattle simplified. Veterinary Parasitology 119, 277–306 PubMed.
  • Dunn A & Keymer A (1986) Factors affecting the reliability of the McMaster technique. Journal of Helminthology 60, 260–262 PubMed.

Other sources of information

  • Taylor M A, Coop R L & Wall R L (2016) Chapter 4 – Laboratory diagnosis of parasitism. In: Veterinary Parasitology. 4th edn. John Wiley & Sons, Chichester, West Sussex, UK. pp 259-262.
  • Gibbons L M, Jacobs D E, Fox M T & Hansen J (2015) McMaster Egg Counting Technique. In: The RVC/FAO Guide to Veterinary Diagnostic Parasitology. The Royal Veterinary College, UK. Website: www.rvc.ac.uk/Review/Parasitology/EggCount/Principle.htm.
  • Taylor M A (2015) Applied clinical parasitology for cattle practitioners. In: Bovine Medicine. 3rd edition. Wiley-Blackwell, Oxford. pp 198-210.
  • MAFF (Ministry of Agriculture, Fisheries and Food) (1986) Reference Book 418: Manual of Veterinary Parasitological Laboratory Techniques. 3rd edn. HMSO, London. pp 12-15.
  • Thienpont D, Rochette F & Vanparijs O F J (1986) Diagnosing Helminthiasis by Coprological Examination. 2nd edn. Janssen Research Foundation, Beerse, Belgium,. pp 205.
  • Whitlock H V (1948) Some modifications of the McMaster helminth egg-counting technique and apparatus. Journal of the Council for Scientific and Industrial Research, Australia 21, 177–180.

Organisation(s)


ADDED