Glossary

Giardia

A microscopic intestinal parasite picked up from contaminated water or feces that can cause soft, greasy diarrhea, mainly in puppies.

Also called: giardiasis, Giardia duodenalis, beaver fever

Giardia is a single-celled parasite that lives in the small intestine. Dogs swallow its tough cysts from puddles, streams, soil, shared yards or another dog's stool. It is most common in puppies, shelter and kennel dogs and dogs that drink outdoors.

Many dogs carry it with no signs. When it causes disease, the typical sign is soft, pale, greasy, smelly diarrhea that may contain mucus, sometimes with weight loss and vomiting. The cysts can be missed on a single sample, so a vet may test more than once with a special antigen fecal test.

Some strains can in theory infect people, so careful hygiene and prompt stool cleanup help. Because the signs resemble many digestive diseases, see a veterinarian instead of guessing, and keep puppies from drinking standing water.

Last reviewed November 8, 2026

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Related terms

Fecal test A laboratory check of a dog's stool for parasite eggs and organisms such as roundworm, hookworm, whipworm and Giardia. Roundworm A common intestinal worm that often infects puppies, frequently from the mother, and can pass to people, especially children.