Colitis is an inflammation of the colon. It is responsible for about 50 percent of cases of chronic diarrhea in dogs. The signs of colitis are painful defecation, prolonged squatting and straining, flatulence, and passing many small stools mixed with blood and mucus. These signs can easily be mistaken for constipation.
The usual cause of colitis is one of the inflammatory bowel diseases. Whipworms are another frequent cause. Fungal colitis is uncommon. It targets dogs with immune deficiency and lowered resistance. Prototheca colitis is a rare disease caused by an algae. It produces a severe form of colitis and can become systemic. Treatment has not been successful.
Colitis is diagnosed by colonoscopy and colon biopsy. Stool specimens are examined for parasites and fungi.
Irritable bowel syndrome describes a diarrhea motility disorder often associated with stress. It tends to occur in high-strung, nervous dogs. Dogs with irritable bowel syndrome have frequent small stools, often mixed with mucus. The diagnosis is based on the exclusion of other causes of colitis.
Treatment is directed toward the underlying condition, often an inflammatory bowel disease. Irritable bowel syndrome can be helped by a high-fiber diet. Bacterial causes of colitis, such as salmonella, campylobactor, and clostridium, will respond to appropriate antibiotics.