Fecal Parasite Egg Identification Reference for Dogs and Cats
Reference for identifying the most common intestinal parasites on a fecal exam - egg or organism appearance, approximate size, and the best diagnostic method for each.
A reference guide, not a substitute for microscopic confirmation.
Sizes and appearances are typical ranges. Always confirm findings against your own microscope's calibration and, when in doubt, a reference laboratory.
Organism type
Nematode (worm)
Roundworms (Toxocara canis/cati, Toxascaris leonina)
Appearance
Thick-walled, subspherical to oval eggs, brown/golden in color; Toxocara has a finely pitted outer shell surface, Toxascaris is smoother.
Approximate size
~75-90 microns
Best diagnostic method
Standard fecal flotation.
One of the most common parasites found on routine puppy/kitten fecals; zoonotic risk (visceral/ocular larva migrans in people, especially children).
Frequently asked questions
Why would a fecal flotation miss whipworm eggs even if the dog has whipworms?
Whipworms shed eggs intermittently, not continuously, so a single sample can be a false negative - repeat testing over several days or fecal PCR panels increase detection.
Why doesn't tapeworm show up on a standard fecal flotation?
Tapeworm eggs are packaged inside shed proglottid segments rather than floating freely in the stool, so diagnosis is typically made by seeing the segments themselves rather than eggs under the microscope.
What's the best test for Giardia specifically?
Standard flotation solutions and technique often miss the much smaller Giardia cysts - a zinc sulfate centrifugation flotation or a fecal antigen ELISA/IFA test is more sensitive.
Which of these parasites are zoonotic (can infect people)?
Roundworms via visceral/ocular larva migrans, hookworms via cutaneous larva migrans, and Giardia in some cases - good hygiene, prompt deworming, and picking up stool promptly all reduce human exposure risk.