Summary
Diarrhea is defined as a condition that yields feces that are softer or more watery than normal.
Diarrhea is a symptom of a wide variety of diseases and events, including dietary indiscretion (like garbage-eating, ingestion of foreign material, and a too-sudden change in diet), gastrointestinal viruses, dietary intolerance, and an overgrowth of intestinal bacteria (many conditions can lead to this last cause, including the aforementioned dietary indiscretion).
Symptoms and Identification
Dogs and cats experiencing diarrhea may defecate more frequently than usual, produce either larger or smaller volumes than normal, and have accidents in the house. Apart from being looser or more watery than usual, their feces may have blood or mucus in it.
Determining the underlying cause is typically the focus of diagnostic testing. This may include...
Fecal examination via miscroscopy
Complete blood count
Serum biochemistry analysis
Abdominal X-rays (with or without contrast)
Abdominal ultrasound
Stool culture
Specific testing for viruses, bacteria, and other pathogens
Specific testing for diarrhea-inciting diseases (Addison's disease, etc.)
Endoscopy and/or colonoscopy
Intestinal biopsy
CT scans (especially if certain cancers are suspected)
Affected Breeds
No breed predisposition has been noted for diarrhea in either dogs or cats. However, some of the underlying causes of diarrhea are doubtless influenced by genetic factors predisposing pets to these diseases. Therefore, breeds of dogs and cats genetically predisposed to any of diarrhea's underlying conditions will naturally be overrepresented.
Treatment
Treatment varies but usually includes special diets and/or medications along with whatever treatment is required to address the diarrhea's underlying cause. These approaches may include (but are not limited to):
Probiotics
Dewormers and other parasiticides
Antibiotics
Dietary changes (temporary or permanent)
Corticosteroids and/or other drugs
Fluid therapy to rehydrate and reestablish normal electrolyte balance
Antiviral drugs
Puppies and kittens, along with small dogs and cats, merit immediately veterinary attention, as they can become dehydrated very quickly. So, too, should pets showing any signs of vomiting, lethargy, or bloody stools see a veterinarian -- immediately.
Veterinary Cost
The cost of diagnosis and treatment of diarrhea depends greatly on its underlying cause. Mere amelioration of the symptoms of diarrhea, however, is typically had for the price of a temporary diet change and the administration of a brief course of probiotics.
Owners of pets with conditions that require expensive hospitalization, elude easy diagnosis, and/or demand a lifetime of management via medication and or diet (often a very expensive proposition) may face extreme expenses in both the long and short term.
Prevention
Prevention of diarrhea is typically undertaken by refraining to offer pets foodstuffs and/or foreign material that do not correspond to their normal dietary repertoire.
Vaccination against specific diseases that lead to diarrheal diseases (such as parvovirus, canine distemper and feline leukemia virus) is also strongly recommended by way of effective prevention.
Pets suffering many disease states that predispose them to diarrhea, however, will typically be unmanageable via these particular methods. In these cases, preventing the underlying cause -- if possible -- is the only rational approach.
References
Fox JG. Enteric bacterial infections. In: Greene CE, ed. Infectious diseases of the dog and cat. 3rd Edition. St. Louis, Mo.: Saunders Elsevier, 2006;339-343.
Marks SL, Kather EJ. Bacterial-associated diarrhea in the dog: a critical appraisal. Vet Clin North Am Small Anim Pract 2003;33(5):1029-1060.
Suchodolski JS, Steiner JM. Laboratory assessment of gastrointestinal function. Clin Tech Small Anim Pract 2003;18(4):203-210.
Weese JS. Microbiologic evaluation of commercial probiotics. J Am Vet Med Assoc 2002;220(6):794-797.
Willard MD. Feline inflammatory bowel disease: a review. J Feline Med Surg 1999;1(3):155-164.
DL. Nutritional management of feline gastrointestinal diseases. Top Companion Anim Med 2008;23(4):200-206.