Chronic enteropathy (CE) is the term now used to describe long-term gastrointestinal disease that lacks a specific diagnosis in canine and feline patients.
Gastrointestinal complaints are common in clinical practice, with acute patients typically resolving with symptomatic and supportive treatment. However, a small subset (1% to 3% of the total caseload) have relapsing or chronic signs in the absence of the usual suspects (such as repeated dietary indiscretion, foreign body ingestion with intermittent partial obstruction, parasites, or enteropathogens).1 Chronic enteropathy (CE) is an umbrella term now used to describe such gastrointestinal (GI) disease in dogs and cats that lasts longer than three weeks and lacks a more specific diagnosis.
The causes of canine and feline chronic enteropathies are multifactorial, and include breed predisposition, environmental factors (e.g. dietary antigens), and intestinal microbiota. While breed specific factors are important and may be useful, such as gluten-sensitive enteropathy in Irish setters7 and antibiotic responsive enteropathy in German shepherds,4 the genetic makeup of the patient in the exam room is unalterable. A change of diet is a leading action generally associated with positive, sometimes long-term, outcomes. Chronic enteropathies can be defined by treatment response according to four general categories: food-responsive, antimicrobial-responsive, immunomodulation-responsive, and non-responsive.
FOOD-RESPONSIVE ENTEROPATHY (FRE)
Similar to food protein-induced enteropathy in people (e.g. gluten sensitivity), about 50% of dogs and cats with CE respond to diet change alone. FRE is more common in younger cats and dogs, whose signs arise from an adverse food reaction, food allergy, and/or food intolerance. It is common for CE patients to have an allergic reaction to certain types of dietary protein. In contrast, food ingredients most likely to cause food intolerances are much more varied and do not require prior exposure. These include carbohydrates (e.g. disaccharides: milk lactose, sucrose and dextrins), pharmacologically active products (e.g. histamine/histidine in certain cheeses and fish), food additives (e.g. food color dyes), and food toxin contamination or overconsumption (e.g. phytohaemagglutinin aka PHA lectin in beans, among many other naturally-occurring plant toxins through to mycotoxins). Improvement can take up to 14 days after switching diets, and several diets may need to be tested. An elimination diet can be effective at identifying allergies or food sensitivities but can be challenging for clients to implement. Some studies report that a hydrolyzed protein diet8 or an easily digestible diet9 are successful at mitigating signs of CE in dogs. As is the case for elimination diets, these special diets can provide short term benefit; however, reducing the diversity of foods provided in the diet in the long run will lead to reduced bacterial diversity in the gut microbiome.
Bacterial dysbiosis is associated with CE and can often be modified by diet. Changes in macronutrient ratios and nutrient bioavailability contribute to shifts in bacterial composition in the digestive tract. Remission in patients with CE induced by a hydrolyzed protein diet was accompanied by decreased abundances of the pathobionts Escherichia coli and Clostridium perfringens, reduced bacterial dysbiosis, and increased levels of the secondary bile acids, lithocholic and deoxycholic acid.10 Improvements in clinical signs are also reported after switching from a high carbohydrate, low protein diet to a low carbohydrate, high protein diet, including raw diets. Likewise, the addition of prebiotic fibers can help firm up stool while also feeding beneficial bacterial populations.
Early life events can influence the likelihood of developing a CE. In a new study, exposure to a high fat, low carbohydrate, non-processed, meat-based diet during early life, and a normal body condition in puppyhood, were significantly associated with less IBD in adult dogs.11 The opposite trend was found with early life exposure to ultra-processed carbohydrate-based diets.
ANTIMICROBIAL-RESPONSIVE ENTEROPATHY (ARE)
Some forms of CE may be alleviated by using antimicrobial treatment to treat a known or suspected bacterial pathogen, to alter the bacterial composition of the gut microbiome, and/or to allow for lower doses of anti-inflammatory medication (immunomodulation). Why such cases respond to antibiotics is often unclear, and an imbalance of the gut microbiome is strongly implicated. Common antibiotics used to treat CE are tylosin, tetracycline, doxycycline, azithromycin, enrofloxacin, rifaximin, and metronidazole. Menozzi et al12 reports that antibiotics can be effective, at least temporarily, at resolving CE signs. However, relapse rates are high. Tylosin has a relapse rate of 86% in 30 days13,14 and 88% within two months,14 and metronidazole has a relapse rate of 100% within six to 12 months.15
In addition to high relapse rates and contributing to antibiotic resistance, the use of antibiotics can produce unhealthy, long term changes in a pet’s gut microbiome. A recent study found that metronidazole had lasting effects on the fecal microbiomes of healthy dogs.16 In our research, we find that prior antibiotic exposure is significantly associated with elevated levels of Escherichia, diarrhea, and bacterial dysbiosis in both cats and dogs (presented at the 2020 ACVIM Forum). Targeted bacteriophage cocktails, such as those designed to target problematic strains of Escherichia coli, provide an alternative to the use of broad spectrum antibiotics.
IMMUNOMODULATION-RESPONSIVE ENTEROPATHY (IRE)
Medications that suppress the immune response in order to reduce inflammation of the gastrointestinal tract lining are the defining treatment for IRE, which is more commonly found in older cats and dogs. Several types of anti-inflammatory drugs are available, some of which are used in combination with antibiotics in more severe cases. Prednisone, prednisolone (preferred for cats over prednisone), chlorambucil (preferred for diabetic cats), mycophenolate, and budesonide have been reported as effective treatments for reducing inflammation within two weeks, with remission rates as high as 78%.17 Reported data is limited, but one study published a relapse rate of 22.7% following immunosuppressant treatment.18
While important and useful, these medications are associated with significant side effects, including negative behavioral shifts and gastrointestinal ulceration. Notari et al19 reported that dogs on corticosteroids were less playful, more nervous, fearful and/or aggressive in the presence of food, and more prone to barking or to startle, to reacting aggressively when disturbed, and to avoiding people or unusual situations. Healthy dogs administered prednisone exhibited gastrointestinal bleeding and ulceration, even in the absence of clinical signs.20 Mycophenolate has recently been reported to produce gut dysbiosis21, 22 but was also reported to reduce gut dysbiosis in spontaneously hypertensive rats.23 Approximately a quarter of canine recipients of mycophenolate experience GI signs.24 While mycophenolic acid acyl glucuronide metabolites, produced by enterocytes and excreted into bile with hepatic metabolism, contribute to osmotic diarrhea by a local irritative effect,25 the gut microbiota play a prominent role in GI toxicity.22 The exact players and mechanisms have yet to be determined.
NON-RESPONSIVE ENTEROPATHY (NRE)
Because CE is a broad term with numerous causes, it’s not surprising that 15% to 40% of cases do not respond to treatment in the short term.26 If a patient is non-responsive to treatment, it is possible that another disease or condition could be contributing to signs. For example, pets can still have a cobalamin deficiency, despite an adequate diet, due to malabsorption as a result of an unbalanced gut microbiome and mucosal inflammation. That said, not all the causes of CE are understood, let alone known. Altering the gut microbiome is an emerging and promising treatment for clinical signs of a gastrointestinal condition, even when the cause is unknown.
FECAL TRANSPLANTATION TO RESTORE KEY BENEFICIAL MICROBES
Should an imbalance in the gut microbiome be suspected or detected in a chronic CE patient, it is possible to augment the intestinal community with probiotics. However, numerous studies report that supplementing with probiotics is unlikely to make a noticeable permanent difference to the gut microbiome. Instead, a fecal microbial transplantation29 (also known as Microbiome Restoration Therapy or MBRT) is the best known practice for restoring a balanced gut microbiota, and contains native gut microbes not found in today’s probiotics. FMT has proven to be effective in both animals30 and humans31 for a number of conditions, such as gut microbiome recovery after antibiotic treatment,32 and to resolve IBD and Clostridioides difficile infections.31 Fecal transplants may be administered a number of ways, including via upper and/or lower endoscopy, enema, or oral delivery.33 Of course, microbiome restoration is most effective when supported by a diet that also feeds these beneficial gut bacteria.
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