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Fecal analysis: parasites

ISSN 2398-2950

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Synonym(s): Fecal flotation; Baermann technique

Overview

  • In patent intestinal parasitic infections eggs will be laid and can be identified in fecal samples.

Uses

Alone

  • Detection of the presence of intestinal parasites.
  • Detection of the presence of respiratory parasites.

Sampling

Source of test material

  • Rectally collected or passed fecal sample.

Quantity of test material

  • >2 g feces.
  • Shedding of parasitic life stages can be intermittent so examination of samples on 3 consecutive days or pooled samples over 3 days increases sensitivity.

Sample collection technique

Flotation

  • Many clinics in the US use zinc sulfate for Giarda cysts. Sheatter sugar for cryptosporidium.
  • 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 (except Metastrongylus).
    • Zinc chloride solution (density 1.89 at 20°C) for trematodes and Metastrongylus.
  • 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.
  • Also sedimentation - Paragoniums.
  • Larval (Baermann) - Aleurostrongylus.
  • Fecal smear for trophozoites of Pentatrichomona sand Giardia.

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.

Direct smear technique

  • A fecal sample approximately 1 mm3 (the size of the head of a match) is mixed with a drop of water on a microscope slide.
  • The slide is examined with a cover slip under the microscope at x40 magnification.
  • The addition of a drop of Lugol's iodine will aid in the detection of Giardiacysts which will be stained yellow.

Quality control

Sample storage

  • Ideally feces should be examined fresh, otherwise they may be stored at 4°C.

Sample transport

Tests

Methodologies

Availability

  • Can be performed in practice with an adequate microscope.

Technique intrinsic limitations

  • Simple technique.
  • The number of parasitic life stages passed varies according to type of parasites.
  • Shedding of parasitic life stages can be intermittent.
  • 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.
  • Alternatives:
    • ELISA Enzyme linked immunosorbent assay (ELISA)  or GiardiaCryptosporidium.
    • Fecal flotation is thought to be more accurate but ELISA snap test for Giardia carries 90% sensitivity, is highly specific and avoids issues of intermittent cyst shedding.

Result Data

Further Reading

Publications

Refereed papers