Giardia, Clostridium perfringens enterotoxin, and Cryptosporidium are important causes of diarrhea in dogs and cats. Tritrichomonas foetus is an important problem in cats. These disorders should be investigated early in the course of diarrhea, whether it is persistent
or intermittent, along with evaluation for dietary causes of GI signs, nematode parasites, bacterial and viral causes, and
acute idiopathic colitis. This group of disorders constitutes a thorough differential list for animals with acute and intermittent
diarrhea (Table 1).
The challenge to veterinarians is in making an accurate diagnosis, so that the best therapy can be instituted as early as
possible. This will then lead to the best opportunity for successful control of the medical disorder. It is also important
to recognize that some animals may have several disorders at the same time, so a thorough diagnostic approach is recommended.
This is why it is often best to run tests for these disorders at the same time, through use of a "fecal diagnostics panel"
that is now available at many commercial laboratories. A single fecal sample is submitted to the lab, and tests for each
of these disorders is done at the same time. This provides a prompt and thorough analysis for important clinical disorders
of the GI tract. The clinician then has more clear direction on how to proceed with treatment, or other diagnostic tests
in the event that none of these disorders is identified.
Table 1: Common Causes of Acute Diarrhea in Dogs and Cats
Giardia is an important cause of diarrhea, and for some patients other GI signs as well. It is an important pathogen in dogs and
cats, as well as humans and other species. Historically, accurate diagnosis of Giardia has posed a significant challenge to veterinary practitioners, but there are now much more sensitive tests readily available
for veterinarians to use on a routine basis. Because of the impact that this organism can have on animals, and also humans
because of its zoonotic potential, it is important that veterinarians perform accurate diagnostic testing on animals to determine
whether or not an animal is infected with Giardia. These notes will emphasize steps for accurate diagnosis, and also management of giardiasis.
Clostridium perfringens enterotoxicosis is a common cause of intermittent diarrhea in dogs and cats. Veterinary practitioners should test for the
enterotoxin whenever faced with a patient that has unexplained diarrhea.
Cryptosporidiosis is now recognized to be a more common disorder in dogs and cats than was previously thought. It can cause
significant abnormalities, and it has zoonotic potential. Cryptosporidiosis can be fatal in people that also are immunosuppressed
(e.g., on chemotherapy or corticosteroids, carriers of HIV). Therefore, it is incumbent on veterinarians to test for this
disorder, as there are important implications to both the patient as well as to humans who may come in contact with an infected
Early Diagnostic Screening in Animals with Diarrhea
**Negative results do not make a rule-out. Be persistent, as retesting can be very important.
Options for Therapy of Nonspecific Diarrhea (GI parasites already ruled out via appropriate testing)
→ Change food (trial 2-3 weeks), may need to try several different foods
→ Colitis signs?
→ Metronidazole or sulfasalazine (Azulfidine)
→ Metronidazole (antibacterial/anti-inflammatory effect)
→ Or, some combination if mono therapy doesn't work (**but don't wait too long on further diagnostics if the response
Diagnosis and Management of Giardia
Standard diagnostic tests used in any practice setting should include fresh saline fecal
smears and zinc sulfate flotation with centrifugation. Zinc sulfate flotation with centrifugation, rather than gravity flotation alone, is a somewhat more sensitve means of testing for Giardia and other parasites. Trophozoites are more likely to be found in loose stools, while cysts are more often found in semi-formed
or formed stools. Performing both zinc sulfate concentration with centrifugation and a
Giardia antigen test together constitutes the most accurate means of evaluating a patient for the presence of Giardia. This has been recognized as the "gold standard" in human medicine, and is true also in veterinary medicine.
Direct Saline Smear
Direct smears should be performed on fresh fecal samples as soon as possible after being passed, but definitely within 1 hour.
A fresh saline smear is made by mixing a drop of feces with a drop of saline on a glass slide. A coverslip is applied and
the preparation is examined immediately under 40x magnification. Trophozoites are pear-shaped and have a characteristic concave
ventral disk. They demonstrate rolling/wobbling motion (e.g., like a falling leaf). Adding a drop of Lugol's solution of
iodine on the edge of the coverslip can be done as an optional procedure and this will enhance the morphologic features of
the organisms and make them easier to find. The iodine kills the parasite, so motion will no longer be seen if this procedure
is used. Differentiation of trichomonads from Giardia is based on a different motion pattern (more forward motion with trichomonads versus rolling motion with Giardia), the absence of a concave disk, a single nucleus, and the presence of an undulating membrane. Identification of Giardia trophozoites is diagnostic, while their absence in fecal samples does not rule out presence of infection.