Canis ISSN: 2398-2942

Fecal analysis: parasites

Synonym(s): Fecal flotation, Baermann technique; ELISA and PCR

Contributor(s): Ian Wright

Overview

  • In patent intestinal parasitic infections eggs will be laid and can be identified in fecal samples.
  • Various life stages (entire worms, worm segments, eggs, casts) of many parasites in the gastrointestinal tract and feces.

Sampling

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Tests

Methodologies

Flotation

  • Feces are suspended in a solution with high specific gravity to make worm eggs float to surface.
    • Saturated sugar or salt solution (prepared by stirring and storing solution for several days) for nematodes and cestodes.
    • Zinc chloride solution (density 1.89 at 20°C) for trematodes.
    • Zinc sulfate solution for Giardiasis Giardia duodenalis.
  • Mix 2 g fresh feces with solution in a beaker and dilute to 90 ml with concentrating solution.
  • Allow mixture to settle for a few minutes and then float a cover-glass on top of the solution.
  • Remove cover-glass after 30 minutes and examine directly.
  • Alternatively, can mix 2 g of feces in saturated salt solution and collect a sample of suspension with Pasteur pipette and fill counting chamber with this.
  • Allow eggs to float to surface and then count for an approximate worm egg count.
  • Eggs which may be seen:
    •  Trichuris vulpis Trichuris vulpis egg.
    •  Capillaria spp Capillaria plica egg.
    •  Toxascaris leonina Toxascaris leonina egg.
    •  Toxocara canis Toxocara canis egg.
    •  Dipylidium caninum Dipylidium caninum egg packet.
    • Taeniid-type eggs Taeniid egg.
    •  Uncinaria stenocephala Uncinaria stenocephala egg.
    •  Ancylostomaspp Ancylostoma caninum egg.

Sedimentation technique for trematode eggs

  • 5 g feces are mixed with 200 ml water in a beaker.
  • The mixture is passed through tea strainer or fine sieve and the material left in the strainer is discarded.
  • The mixture is allowed to stand for 10 mins and then 75% of the supernatant is removed.
  • The beaker is refilled with fresh water and the previous step repeated.
  • This is continued until the supernatant is clear.
  • 90% of the supernatant is then removed and the remainder poured into the petri dish.
  • The sediment is then examined under a dissecting microscope or samples mounted on slides for microscopic examination.

Baermann technique for lungworm larvae

  • A rubber hose is attached to the funnel, forming a watertight seal.
  • The two are suspended on a clamp stand with enough space underneath the tubing to allow collection of samples.
  • A clamp is placed on the end of the tube. This should be able to be easily opened and closed to allow collection of the sample without spillage and possible loss of larve.
  • Warm water is placed into a funnel until it is mostly filled.
  • The fecal sample is wrapped in gauze and place in the water in the funnel. A stick or thin metal pole is placed through the gauze so it may be suspended in the water.
  • The warmth of the water activates the larvae in the sample but they are unable to swim upwards against gravity. As a result, they drop through the gauze and down the funnel into the tubing.
  • After 12-24 hours the clamp is released and 10-15 mL of water can be drawn off into a test tube. The sample can then be centrifuged and the resultant plug examined for larvae. The sample can then be centrifuged and the resultant plug examined for larvae. If a centrifuge is not available the larvae can be allowed to settle to the bottom of the tube over an 8-12 hour period.
  • Adding Lugol's iodine before examination kills the larvae, making identification easier.

ELISA and PCR coproantigen tests

  • Fecal ELISA Enzyme linked immunosorbent assay (ELISA) testing for Echinococcus multilocularis Echinococcus multilocularis found to be 80% sensitive and this reached 93% in foxes with worm burdens over 55 in number. Specificity was 95-99%.
  • PCR Polymerase chain reaction testing of feces for Echinococcus multilocularis found to have a sensitivity of 94% and a specificity of 100%.
  • Fecal Snap test for Giardia spp antigen carries 90% sensitivity and 100% specificity.

Availability

  • Can be performed in practice with an adequate microscope.

Validity

Sensitivity

  • Variable, depending on species of parasite, experience of operator and technique used.

Specificity

  • 100% with experienced operator.

Predictive value

  • Not determined.

Technique (intrinsic) limitations

  • Simple techniques.
  • The number of life stages passed in feces varies according to type of parasites.
  • Egg laying decreases as the worms age and often the host develops immunity which also reduces egg laying capacity of parasites.
  • Consistency of feces may affect egg count as in loose feces the eggs will be diluted.
  • Some parasites pass parasitic life stages intermittently.

Technician (extrinsic) limitations

  • Experience is required to identify eggs/segments/larvae of individual parasite species.

Result Data

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Further Reading

Publications

Refereed papers

  • Recent references from VetMed Resource and PubMed.
  • Dinkel A, Kern S, Brinker A, Oehme R, Vaniscotte A et al (2011) A real-time multiplex-nested PCR system for coprological diagnosis of Echinococcus multilocularisand host species. Parasitol Res 109, 493-498 PubMed.
  • Conboy G (1996) Diagnostic parasitology. Can Vet J 37(3), 181-182.
  • Deplazes P & Eckert J (1996) Diagnosis of the Echinococcus multilocularis infection in final hosts. Applied Parasitology 37, 245-252.
  • Nicholls J, Obendorf D L (1994) Application of a composite fecal egg count procedure in diagnostic parasitology. Vet Parasitol 52(3-4), 337-342.


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