Giardia infections can present with a wide range of clinical signs. Further complicating the diagnosis is the intermittent shedding of cysts and identifying the parasite. The motile trophozoites are found in fresh feces. The cyst forms can be difficult to find and correctly identify because sugar flotation solutions distort the cysts. Zinc sulfate flotation solutions are better, but cysts can easily be missed if staff are inexperienced or poorly trained. In this study, a commercial point-of-care enzyme-linked immunosorbent assay (IDEXX SNAP Giardia Test, IDEXX Laboratories; was used to determine the prevalence of Giardia infections in dogs and cats with vomiting and diarrhea. Data were collected from across the United States on a volunteer basis. The prevalence rates were 15.8% of 16,114 dogs tested and 10.8% of 4978 cats tested. Among dogs, Giardia species were most common in New England and the Midwest. In cats, Giardia species were common in New England, the western Midwest, and the northern South-Central states (Oklahoma, Arkansas, Mississippi, and Tennessee). The study did not investigate whether Giardia caused the clinical signs displayed by the animals. The authors concluded that the test was easy to use and that Giardia species were common in dogs and cats with gastrointestinal signs.

COMMENTARY: This article describes the first study concerning the prevalence of Giardia spp. infections in dogs and cats across the U.S. based on the highly sensitive IDEXX SNAP Giardia test. A large population of dogs and cats was used to analyze the presence of Giardia spp. antigen in fecal samples of patients with vomiting and/or diarrhea. The authors report a relatively high prevalence of Giardia infections. It is important to note that the presence of Giardia spp. antigen in feces does not necessarily indicate that the clinical signs are caused by this agent. Giardia spp. (as well as some other protozoa) are known to inhabit the enteric lumen of healthy animals, and shedding can occur because of diarrhea caused by an unrelated disease process, which should therefore always be ruled out. On the other hand, if no other cause for the clinical signs can be identified, a positive test for Giardia in a dog or cat with gastrointestinal signs is always an indication for treatment. Patients with Giardia infections are reported to generally respond well to metronidazole, but this antibiotic has the potential to cause central nervous system toxicity, especially in young kittens. Furthermore, it should not be used long term due to potential accumulation in the body. A drug with fewer side effects is fenbendazole, which eradicates Giardia infection at 50 mg/kg once a day for 3 to 5 days.

Prevalence of Giardia in symptomatic dogs and cats throughout the United States as determined by IDEXX SNAP Giardia test. Carlin EP, Bowman DD, Scarlett JM,  et al. VET THER 7:199-206, 2006.