Worms and giardia can cause small intestinal diarrhea, mostly in young animals. Foreign bodies including bones, sticks and other objects can pass through the stomach and get stuck in the intestine causing both diarrhea and vomiting. These same foreign materials may pass through the intestinal tract without getting stuck but may damage the lining of the intestinal tract causing diarrhea. Dietary indiscretion or a sudden change in diet can cause diarrhea with or without vomiting. Food allergies in dogs and cats can cause diarrhea, vomiting or itchy skin.
Toxins including lead and insecticides can cause diarrhea usually with vomiting.
In IBD the walls of the intestine contain abnormal numbers of inflammatory cells which can be eosinophils, lymphocytes or plasma cells. The cause of IBD is not known but is suspected to be an allergic reaction to components of food, bacteria or parasites. Basenji dogs may develop a severe inflammatory bowel disease. Tumors of the intestine are another cause of diarrhea usually occurring in older pets. Lymphosarcoma occurs in both dogs and cats and can either be a single or multiple masses in the intestine or the abnormal lymphocytes may be spread through out the intestine.