In many cases of diarrhoea, a specific cause is not always identified, and patients respond to symptomatic and supportive treatment. In other cases, especially where the diarrhoea is severe or prolonged, investigations need to be done to determine the underlying cause and appropriate treatment.
Diarrhoea is most commonly caused by primary intestinal disease but can less commonly be secondary to a systemic disease, especially in older animals, therefore investigations are often necessary.
Intestinal causes of diarrhoea:
Diet change - sudden changes in diet including scavenging, new treats, human food or being overfed, can cause mild short-lived diarrhoea. Often this settles down as the intestine adapts to the new diet, or other food is stopped. This is particularly common in younger animals. Some animals may not be able to tolerate certain foods, and in these cases the diarrhoea will not resolve until the diet has been changed.
Dietary allergy - seen more and more commonly, some patients may develop an allergy (hypersensitivity) to food. In this case the specific food needs to identify and eliminated from the diet.
Infectious causes - Viruses are uncommon, but Parvovirus can cause severe diarrhoea and is life threatening (this is included in the annual vaccine). Bacterial causes include Salmonella, Campylobacter and E. Coli, which can be picked up by eating uncooked contaminated food or rotten food. Parasitic causes include worms, giardia and coccidian which is passed in the faeces of infected animals. Infectious agents will frequently affect more than one animal in a household, but animals with a sensitive disposition or concurrent illness are more likely to show clinical signs. Some infectious causes are zoonotic (transferable to humans) therefore it is particularly important at this time to observe good hygiene. Young children, immune-compromised individuals and the elderly should be particularly careful.
Pancreatic insufficiency and pancreatitis - pancreatic disease is an important cause of diarrhoea in dogs. The pancreas is responsible for producing important digestive enzymes and when these are not produced (pancreatic insufficiency) diarrhoea will result as food cannot be properly digested. If the pancreas is inflamed this can be quite painful and usually the patient will become dehydrated as a consequence and require hospital treatment.
Inflammatory bowel disease - this results in chronic (long-term) persistent or intermittent diarrhoea and/or vomiting. This is quite uncommon in dogs.
Intestinal tumours - these are generally uncommon in dogs. They can cause disease and clinical signs by interfering with the normal absorption of food and also by causing partial obstruction of the intestine.
Benign polyps and growths - although uncommon, occasionally benign growths or polyps can develop in the intestine and often cause disease through gradual partial obstruction to the passage of food.
Systemic causes of diarrhoea:
Other disease processes affecting the liver, kidneys and endocrine system can lead to diarrhoea. If the diarrhoea is severe or persistent or a cause cannot be identified, then blood sampling is required to investigate further.
Your vet will first examine your dog and take a history, before deciding if further tests are necessary.
One of the difficulties is that there are so many different potential causes of diarrhoea, in some cases quite extensive investigations may be needed to determine the cause.
If the diarrhoea has developed recently, is relatively mild, and the patient is still bright and alert, your vet may simply suggest symptomatic treatment to see if the problem resolves. If not, or if the diarrhoea is more serious, further investigations may be warranted.
Vets will try to do these investigations in a logical and structured way so that potential causes of the diarrhoea are not missed. Investigations may include:
- Blood and urine tests to rule out systemic disease and things like pancreatitis, liver and kidney disease and reduced intestinal function.
- Examination of faecal samples - these can be assessed for the presence of parasites (often a 3day pooled faecal sample is collected for this as some parasites do not shed in every stool), and to culture for the presence of pathogenic bacteria.
- Radiographs (X-rays) and ultrasound are often used to examine the gastrointestinal tract and to detect physical abnormalities.
- Endoscopy - this is where a small medical camera is passed into the intestine (either through the mouth and/or through the anus) under general anaesthesia, so that the lining of the intestine can be examined, and biopsies can be collected. This can be valuable, especially where tumours, polyps or inflammatory bowel disease are suspected.
- Exploratory surgery - this is sometimes done as an alternative to endoscopy or if endoscopy has failed to provide an answer. It allows all of the intestines to be examined (along with organs such as the liver and pancreas) and provides an excellent way of getting biopsies from different parts of the intestine.
Treatment of diarrhoea can be either specific or supportive. Most cases of moderate to severe diarrhoea will need some form of supportive treatment but specific treatment requires identifying the underlying cause and targeting the treatment at this.
Do not starve - it was traditionally thought that starving the intestines for 24hours helps resolve the diarrhoea. However recent research has shown that the intestines need to be fed to provide energy to recover. As soon as the patient is able to keep food down, they should be offered little and often of the bland diet.
Dietary therapy - switching to a simple, highly digestible diet is often very helpful in managing diarrhoea irrespective of the underlying cause. A home-cooked diet of chicken or fish with a little white rice or pasta is suitable in the short-term (2-3days), but for longer-term management a more balanced diet is preferable and your vet will be able to recommend a number of options. Royal canin gastrointestinal diet is chicken and rice based but also contains probiotics to help the intestines recover and to firm up the faeces. In addition, a diet trial is an important part of the investigation of persistent diarrhoea to rule out dietary intolerance or dietary allergies. In these cases, special diets available from your vet are often used.
Probiotics - probiotics are live bacteria that can be given with food. They can help in the management of diarrhoea by improving intestine health. Canikur is the most common probiotic prescribed. It is clay based which helps to bulk out the faeces.
Fluid intake - with more severe diarrhoea it is possible for your pet to become dehydrated, so attention must be given to fluid intake and your vet may even suggest we keep your pet in to administer intravenous fluid therapy.
Specific therapies will depend on the underlying cause of the diarrhoea, but these may include:
- Anti-bacterial and anti-parasitic drugs – if infectious agents are identified then specific drugs may be available to treat your dog and eliminate them. However, antibiotics should never be used indiscriminately as they can cause exacerbation of diarrhoea, interfere with other investigations, and unnecessary use of antibiotics simply promotes bacterial resistance.
- Anti-inflammatory and immunosuppressive drugs – these are often used in the management of inflammatory bowel disease.
- Surgery and/or chemotherapeutic drugs – these can be useful in the management of intestinal tumours.
- Vitamin B12 – weekly injections of vitamin B12 are generally used when B12 deficiency has been diagnosed.
- Pancreatic enzymes – replacements need to be given daily in the case of pancreatic insufficiency.
The prognosis depends on the cause of the diarrhoea - diseases which are easily managed with diet and/or drugs carry a good prognosis, and many cases will completely resolve with appropriate therapy. In other cases, e.g. pancreatitis, ongoing therapy may be required, and repeat episodes can be common.