What is Giardia?

Giardiasis is caused by the protozoan parasite Giardia duodenalis (also called Giardia lamblia or intestinalis), a microscopic organism that lives in the small intestine and is shed in feces as resistant cysts. Transmission occurs mainly through ingestion of water, soil, or food contaminated with these cysts, which makes the disease common in places with many animals, such as kennels, shelters, and daycare facilities.

The most common symptoms are diarrhea (sometimes with mucus, but usually without blood), yellowish or greenish stools, gas, weight loss, and, in some cases, vomiting. Many infected animals, especially adults, show no symptoms at all and simply shed cysts into the environment, which makes controlling the disease in groups of animals more difficult.

Diagnosis is made through a fecal exam (sometimes repeated, since cyst shedding is intermittent), and treatment uses specific antiparasitic medication along with thorough environmental hygiene. There is a risk of transmission between species, including to humans, although the strains most common in dogs and cats have low zoonotic potential. See a veterinarian if a pet has diarrhea lasting more than 2 to 3 days, especially puppies and kittens, who dehydrate quickly.