Artifacts and Pseudoparasites

When examining feces for parasites, be mindful of a) characteristics of the specific parasitic material you are searching for, b) non-parasitic material that may be included in the sample, and c) pseudoparasites which may be present, but are not harmful to the host.

Recognition of Parasitic Material

Many things will float in a fecal flotation (anything with a specific gravity of less than about 1.2), so how do you decide if something is a parasite egg or cyst? Here are a couple of guidelines:

• Know the shape and size of the eggs and cysts you could potentially find in the feces of the animal you are examining.
• Remember: Parasite eggs and cysts are, in general, regularly shaped and fall within a size range of about 2 to 200µm.

A coccidial oocyst (oval, about 20 µm long), a tapeworm egg (an unusual shape but still regular i.e. the sides are straight and the corners smooth), and a nematode egg (oval, about 200 µm long).

Recognition of Non-parasitic Material

Plant Cells Note the irregular boarders of the cell membrane surrounding the lipid storage product.
Air bubbles, Spores, or Pollen Grains Although the pollen grain in the image to the immediate right is regular in shape and within the size range, its contents are homogenous in nature, i.e. it is filled, wall to wall, with one undifferentiated substance. Air bubbles are perfectly round and empty.
Fungal Spores These are very common in the feces of herbivores. Note that although they are of the right size and shape, their contents are homogeneous and there is the remnant of the hyphae still attached to one end. If the hypha has completely broken off, a curved depression would be evident where it once was attached.
Plant Spines Plant spines are sometimes mistaken for nematode larva, however, a nematode larva would have a head and a tail (they aren't found broken in the middle).

 

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Recognition of Pseudoparasites

A pseudoparasite ("false parasite") is a parasite which is found in the feces of a host which it was not infecting, rather it just passed through after the animal ate the original host or material contaminated with the eggs or cysts.

	Nematode Larvae In this enlarged view of the anterior end of the larva, the double bulbed esophagus can be noted. This generally identifies the nematode as a free-living species.
	Ciliates Although these protozoa are found inhibiting the gut of the horse, they are normal non-pathogenic inhabitants and not parasites.
	Sporocyst of Monocystis sp. Monocystis sp. is a parasite of earthworms. The dog ate an earthworm, digested it, and freed the sporocysts which then passed out with the feces.
	Mites These are grain mites found in the feces of dogs, and are contaminants of stored food. Skin dwelling mites may also be found in the feces if the dog is infested and has been biting at the irritated skin.
	Mite Eggs Mite eggs are about 300µm, which is too large to be a nematode egg. Other mite eggs resemble strongyle-type eggs of nematodes but, again, are too large. Mite eggs find their way into the feces in the same manner as mites.

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