Giardiasis is defined as the disease state caused by a variety of parasitic protozoan organisms of the genus, Giardia. This disease, which typically affects the intestinal tract, is considered common in dogs, cats and humans.

In fact, giardiasis is considered so common that research indicates an infection rate between 1 and 39 percent of all shelter pets (dogs and cats), worldwide. Another Australian study demonstrated that 80 percent of all cats in one major city, Perth, came up positive on a highly sensitive test for Giardia organisms. These results intimate that giardiasis is a much more complex disease than we'd previously understood it to be.

Indeed, plenty of animals that test positive for infection don't show any clinical signs. This may be because different strains affect animals differently. It may also suggest that the disease is self-limiting, requiring no treatment before the animal's body eventually vanquishes the infection.

Giardia is considered transmissible only via ingestion of the organisms themselves. As such, the presence of an intermediary environment, typically a fetid or watery one, is involved in most cases of giardiasis. Direct transmission from one animal to another -- or between humans and animals -- is only possible via the fecal-oral route.

Symptoms and Identification

If they experience any clinical signs at all, most pets will suffer a pattern of diarrhea consistent with small intestinal inflammation. Profuse watery diarrhea, sometimes explosive, is its hallmark. Other gastrointestinal symptoms are also possible, including straining to defecate, blood in the stool, and even vomiting. Most of these signs are not life-threatening.

Diagnosis of Giardia can usually be made by fecal examination using a routine zinc sulfate fecal flotation solution.

Several ELISA tests have been marketed for use in humans. These tests identify Giardia-specific proteins in the stool and they've been found to be very effective in identifying Giardia infection in cats and dogs. Because of their high cost and similar efficacy to fecal flotation using a zinc sulfate solution, most veterinarians do not employ these tests.

Unfortunately, as many as 30 percent of giardiasis cases can't be confirmed via testing as the organism doesn't always lend itself to ready identification. Reexamination after a period of time is always warranted.

Alternatively, in cases where giardiasis is suspected but can't be confirmed via testing, a therapeutic trial might be indicated by way of diagnosis. Unfortunately, however, it's impossible to know whether the cessation of symptoms is due to the treatment's efficacy against Giardia.

In the less common cases in which potentially life-threatening symptoms are present, a broader range of diagnostic tests are indicated: fecal examinations for parasites, complete blood count (CBC), biochemical profile (serum chemistry), urinalysis, and survey abdominal radiographs. Additional tests may be needed to identify specific conditions.

Affected Breeds

Any breed of dog or cat can be affected by giardiasis.


Treatment of giardia infection typically includes drug therapy: While the use of metronidazole or fenbendazole is most common, furazolidone and quinacrine (not available in the US) are also employed.

Veterinary Cost

Because definitive diagnosis is typically relatively straightforward, diagnosis, can typically be had for the price of a fecal examination ($20 to $50, on average). Treatment is usually inexpensive as well but varies according to size. $20 to $100 is typical of uncomplicated giardiasis treatment.

Pets with unconfirmed giardiasis, giardiasis complicated by other diseases or severe symptoms, however, may require hundreds or even thousands of dollars to diagnose definitively and treat.


Prevention generally isn't considered feasible for giardiasis patients.


Barr SC, Bowman DD. Giardiasis in dogs and cats. Comp Cont Educ Pract Vet 1994; 16: 603-610.

Leib M, Dalton M, King S, et al. Endoscopic aspiration of intestinal contents in dogs and cats: 394 cases. J Vet Int Med 1999; 13: 191-193.

Leib M, Matz M. Diseases of the intestines. In: Leib M, Monroe W (ed.). Practical Small Animal Internal Medicine. Philadelphia, WB Saunders, 1997; 685-760.

Leib MS, Zajac AM. Giardia: Diagnosis and treatment. In: Bonagura JD, Kirk RW (ed.). Current Veterinary Therapy XII. Philadelphia, W. B. Saunders Company, 1995; 716-720.

Leib M, Zajac A. Giardiasis in dogs and cats. Vet Med 1999; 94: 793-802.

Monis PT, Thompson RCA. Crytosporidium and Giardia-zoonosis: fact or fiction? Inf Gen Evolut 2003; 3: 233-244.

Thompson RCA. Giardiasis as a re-emerging infectious disease and its zoonotic potential. Int J Parasitol 2000; 30: 1259-1267.

Zajac AM. Giardiasis. Comp Cont Educ Pract Vet 1992; 14: 604-611.

Zimmer JF, Burrington DB. Comparison of four techniques of fecal examination for detecting canine giardiasis. J Am Anim Hosp Assoc 1986; 22: 161-167.