This is probably not the issue, but when I hear about loose stools, I think of this awful gut sickness GIARDIA…
Giardia in Dogs and Cats:
More Common Than
Stanley L. Marks, BVSc, PhD, DACVIM (Internal Medicine, Oncology), DACVN
University of California School of Veterinary Medicine
Giardia is an important cause of outbreaks of waterborne
infection due to contamination of raw municipal water, backcountry
streams, and lakes with human effluent or infected
animal feces.1 The overall prevalence of Giardia in dogs in
North America has been reported at about 8%, with much
higher levels in puppies (36% to 50%) and in animals in shelters
and kennels (up to 100%).2 The prevalence in cats tends
to be lower, at about 4%.2 As with dogs, infection in cats is
more common in animals younger than 3 years of age. Most
infections are subclinical or show only transient softening of
the stool early in the infection, although diarrhea may be acute
and short-lived, chronic, or intermittent in dogs and cats.
The diagnosis of Giardia infection traditionally has depended
on microscopic identification of trophozoites or cysts in feces
of affected animals. However, microscopic diagnosis of Giardia
infection can be difficult because cysts are delicate and may
be shed intermittently. Many artifacts (e.g., grass pollen, yeast)
mimic to varying degrees the morphology of Giardia cysts, and
care must be exercised in differentiating these from Giardia. A
commercially available direct immunofluorescence assay can
be used to facilitate the diagnosis of Giardia; however, this test
requires a fluorescent microscope for detection of the cysts.
There are also human ELISA kits available that can detect Giardia
antigen in fecal specimens; however, the performance
characteristics of many of these kits have not been well studied
in dogs and cats, and these assays are relatively
Recently, a novel SNAP Giardia Test Kit (IDEXX Laboratories,
Inc., Westbrook, ME) for detection of Giardia antigen
in canine and feline feces was released. This test is a rapid
in-house enzyme immunoassay that can be conducted on
fresh feces, previously frozen feces, or feces stored at 2˚C
to 7˚C for up to 7 days. This test represents the first commercially
available ELISA designed specifically for dogs and
cats and has the added advantages of simplicity, rapid
completion (8 minutes), and low cost.
Treatment for Giardia should include bathing the infected
animal and decontamination of the animal’s environment with
a quarternary ammonium–based disinfectant. Giardiacidal
drugs used in dogs and cats include the following:
• Metronidazole, 50 mg/kg PO q24h for 5 days, is only
about 67% effective in dogs,3 can cause neurotoxicosis,
is expensive, and is suspected of being teratogenic.
• Albendazole, 25 mg/kg PO q12h for 2 days, is effective in
dogs; however, the drug can cause pancytopenia secondary
to bone marrow suppression.4
• Fenbendazole is generally safe and effective in dogs and
cats when administered at a dose of 50 mg/kg PO q24h
for 3 days.5
• Quanacrine, 6.6 mg/kg PO q12h for 5 days, is effective in
dogs; however, the drug can cause anorexia, lethargy,
Recently, a commercial Giardia vaccine (GiardiaVaxTM, Fort
Dodge Animal Health, Overland Park, KS) containing chemically
inactivated trophozoites has been prepared and licensed
for use in dogs and cats in the United States. Efficacy studies
conducted in puppies and kittens revealed that fewer vaccinated
animals developed diarrhea after oral challenge, and
diarrhea in vaccinated animals was of short duration compared
with controls. Vaccination also reduced the duration of
cyst shedding and the number of cysts shed in the feces
when compared with control animals.6 The use of Giardia
vaccination as immunotherapy in naturally infected dogs and
experimentally infected cats has had mixed results, although
additional studies are warranted to determine the efficacy of
vaccination combined with giardiacidal drugs.
1. Marshall MM, Naumovitz D, Ortega Y, Sterling CR:
Waterborne protozoan pathogens. Clin Microbiol Rev
2. Kirkpatrick CE: Enteric protozoal infections, in Greene CE
(ed): Infectious Diseases of the Dog and Cat. Philadelphia,
WB Saunders, 1990, pp 804–814.
3. Zimmer JF, Burrington DB: Comparison of four protocols for
the treatment of canine giardiasis. JAAHA 22:168–172, 1986.
4. Meyer EK: Adverse events associated with albendazole and
other products used for the treatment of giardiasis in dogs.
JAVMA 213:44–46, 2001.
5. Barr SC, Bowman DD, Heller RL: Efficacy of fenbendazole
against giardiasis in dogs. Am J Vet Res 55:988–990, 1994.
6. Olson ME, Ceri H, Morck DW: Giardia vaccination. Parasitol
Today 16:213–217, 2000.