Acute and chronic diarrhea in dogs and cats: Giardiasis, Clostridium perfringens Enterotoxicosis, Tritrichomonas foetus, and Cryptosporidiosis (Proceedings)
Nov 01, 2010
CVC IN SAN DIEGO PROCEEDINGS
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.
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 animal.
**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
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.