5) Inflammatory bowel disease.
This is a catch-all term that is given for chronic episodes of diarrhea linked to one of several conditions including allergies, parasitic infection, lowered immune system, diseases such as colitis. Symptoms include persistent diarrhea, a low-grade fever, weight loss, lethargy, and/or vomiting.
This is more common with dogs that are 5+ years, though it can happen to younger dogs as well. This is diagnosed with a combination of blood testing, urinalysis, stool testing, and other tests. Treatment may include antibiotics, corticosteroids, and medications to protect the lining of the intestines. In many cases a change to a different food which includes a switch in both protein and carb sources can help.
6) Ingestion of poisonous foods or toxins.
This can cause diarrhea, among other symptoms. Foods toxic to canines include anything sweetened with Xylitol (most often found in sugarless candy & chewing gum), chocolate, coffee (both the grounds and the beans), grapes, raisins, the core of most fruits, any beverage with caffeine, macadamia nuts, onions, garlic (only in large quantities), certain moldy walnuts, and raw potatoes.
Toxic substances that dogs are sometimes known to get into include cleaning products, antifreeze, insecticides, fertilizer, and medications for humans (Advil is among the top 10 reported toxins leading to pet poisoning).
7) Parasitic infection.
This includes roundworms, hookworms, whipworms, coccidia, and giardia. All newborn puppies should be properly de-wormed by the veterinarian and fecal testing should be performed during yearly wellness visits to check for intestinal parasites. Most of these parasitic infections are treated with multiple treatments of de-wormer medication, along with owners sanitizing both the indoor and outdoor areas of living space. Both coccidia and giardia are treated with antibiotics and also a cleaning of both environment and the dog, since these can shed onto the coat.
8) Other less common but possible reasons for diarrhea include:
Kidney disease, liver disease, cancer, lymphangiectasia, pancreatitis, hemorrhagic gastroenteritis, and Rickettsial (a tick-transmitted disease).