Causes of Canine Diarrhea
Diarrhea is usually a symptom of some underlying medical condition; it is not a disease or illness in and of itself. Nonetheless, diarrhea in dogs does require prompt attention and treatment, both for the comfort and welfare of the affected animal and for the benefit and wellbeing of its owner. Diarrhea can be acute, which means that it comes on quickly, typically is quite severe and then goes away. It also can be a chronic condition, which means that the dog’s symptoms come on gradually and persist over time. Chronic diarrhea usually is milder than acute diarrhea. Unless the underlying reason for diarrhea is diagnosed and resolved, this unpleasant condition can wax and wane over an indefinite period of time.
There are 4 primary mechanisms that cause diarrhea. They are:
- Osmotic: excess substances in the intestines (usually dietary) draw in water, which overwhelms the capacity of the intestines to absorb the fluid.
- Secretory: over-secretion of ions and other substances by the small intestine overwhelms intestinal absorptive capacity.
- Exudative: increased permeability of the intestinal lining from parasitic, foreign body or bacterial infiltration or ulceration causes fluid, serum proteins, blood and/or mucus to leak into the intestinal tract.
- Abnormal motility: movement of digesta through the gastrointestinal tract can be either too slow (hypomotility) or too fast (hypermotility).
There are dozens of diseases, disorders, substances and conditions that can cause diarrhea in dogs by one or more of the above mechanisms. Some of the most common causes of acute-onset diarrhea are:
Local irritation of the intestinal lining (mucosa) by chemical or infectious agents (gastroenteritis or gastrointestinal upset); can be caused by environmental overcrowding, poor sanitation or compromise of the dog’s immune system.
Dietary indiscretion (eating garbage, rotten or rancid food or indigestible materials)
Abrupt dietary changes
Metabolic diseases, such as Addison’s Disease/hypoadrenocorticism, liver (hepatic) disease, kidney (renal) disease, pancreatic disease (pancreatitis)
Ingestion of poisonous or toxic substances (heavy metals, organophosphates, steroids, anti-inflammatory drugs, antibiotics, anthelmintics/dewormers, poisonous plants, others)
Physical obstruction or foreign bodies in the intestine
Viral infection (canine parvovirus, coronavirus, rotavirus, distemper virus)
Bacterial infection (Salmonella, Campylobacter, Clostridum, Escherichia coli, others; increased risk when feeding a raw diet, especially in young or immunocompromised dogs)
Extreme stress (travel, rehoming, relocation, introduction of a new pet or human family member)
Internal parasite infection (hookworms, ascarids/roundworms, whipworms, strongyles, cestodes, Giardia, coccidia, Entamoeba)
Salmon poisoning (Neorickettsia)
Fungal infection (histoplasmosis)
Causes of chronic diarrhea may include one or more of the following:
Dietary changes (in substance or amount)
Kidney (renal) disease
Liver (hepatic) disease
Inflammatory bowel disease (IBD)
Irritable bowel syndrome
Bacterial infection (Campylobacter jejuni, Salmonella, Escherichia coli, Yersinia pseudotuberculosis)
Viral infection (parvovirus, coronavirus, rotavirus, distemper virus)
Fungal infection (histoplasmosis, aspergillosis)
Benign rectal polyps
Exocrine pancreatic insufficiency (EPI)
Chronic small intestinal bacterial overgrowth (SIBO)
Adverse drug reactions
Addison’s Disease (hypoadrenocorticism)
Preventing Diarrhea in Dogs
Owners should feed a high quality diet and take reasonable steps to prevent dietary indiscretion. Dogs should not have their diet changed suddenly and should not be allowed to eat non-digestible items, such as plastic, wood, hair and garbage. Overly stressful activities should be avoided as much as possible.