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Diarrhea, Antibiotic-Responsive/Small-Intestinal Dysbiosis 261

• Cats appear to have higher bacterial counts are altered and EPI has been ruled antibiotic therapy (tylosin) may be required,
8
5
out.
(10 -10 CFU/mL), and anaerobic bacteria • Serum trypsin-like immunoreactivity to rule although only when underlying causes have
VetBooks.ir • In the normal host, overgrowth of normal • Rectal scrape (p. 1157) cytology to rule out of tylosin therapy with diet modification Diseases and Disorders
(Bacteroides, Fusobacterium, Eubacterium)
definitively been addressed. The combination
predominate.
out EPI
has been useful in dogs with ARD (i.e.,
flora or pathogens is prevented by protective
other causes of diarrhea
mechanisms such as gastric acid secretion, • Endoscopic mucosal biopsies demonstrate TRD). Tylosin can be empirically tapered
to 10-25 mg/kg PO q 24h for long-term
intestinal motility (peristalsis and interdiges- minimal inflammatory infiltrates/changes therapy.
tive migrating complexes), pancreatic and in primary ARD; in secondary ARD, GI • Recognize underlying contributory disorders
bile antimicrobial secretions (enzymes, biopsies may demonstrate the underlying that may be associated with ARD/SIBO and
immunoglobulins), and local enteric immu- primary disease. may require other treatment.
noglobulin production. Disruptions in these • Fecal culture: rarely helpful except for the
protective mechanisms can predispose to isolated case of Salmonella or Campylobacter Nutrition/Diet
ARD. infection. Duodenal juice culture is of no Highly digestible, low-fat diets are recom-
• The pathophysiologic mechanism of ARD diagnostic use. mended and may reduce food-related (due
is thought to involve intraluminal effects of • Dysbiosis index (dogs only) to intolerance or poor nutrient digestibility)
proliferating bacteria, damage to mucosal ○ The fecal dysbiosis index (DI) is a causes of dysbiosis.
enterocytes, injury to brush border enzymes polymerase chain reaction (PCR)–based
and carrier proteins, secretion of enterotoxins, assay that quantifies the abundances of Drug Interactions
deconjugation of bile acids, hydroxylation major bacterial groups in fecal samples Metronidazole is a radiation sensitizer in animals
of fatty acids, decreased mucin production, and summarizes them in a single undergoing concurrent radiation therapy.
bacterial competition for nutrients and number.
vitamins (i.e., cobalamin), and increased ○ A DI below 0 indicates a normal fecal Possible Complications
mucosal permeability. microbiota; a DI above 2 indicates Central nervous system signs occur with high-
• The net result is intermittent small-bowel dysbiosis due to chronic enter- dose metronidazole (do not exceed 30 mg/kg/d,
diarrhea with or without weight loss opathy or EPI. A DI between 0 and 2 is and do not exceed 2 weeks of treatment at
and variable vomiting, anorexia, and equivocal. this dose).
malnutrition due to malabsorption of fats, ○ Due to microbiota differences along the
carbohydrates, proteins, and fat-soluble intestine, evaluation of the fecal DI may Recommended Monitoring
vitamins. not accurately reflect microbiota changes Monitor for recurrence of diarrhea after
in the small intestine. Concurrent evalua- therapy.
DIAGNOSIS tion of serum concentration of cobalamin/
folate with assessment of the fecal dys- PROGNOSIS & OUTCOME
Diagnostic Overview biosis index may help in the diagnosis
Most cases of ARD are diagnosed empirically, of dysbiosis. Usually excellent; may require chronic treat-
based on a response to a course of oral antibiot- ment, especially if underlying GI disease is
ics implemented when other common causes TREATMENT present and ARD is secondary
of diarrhea have been ruled out.
Treatment Overview PEARLS & CONSIDERATIONS
Differential Diagnosis Resolution of diarrhea with appropriate
See Diarrhea, Section 3 (p. 1213). antibiotic therapy Comments
• Intestinal parasitism (helminthiasis, giardiasis) • Primary (idiopathic) ARD is rare; always
• Dietary intolerance/hypersensitivity Acute General Treatment evaluate for underlying GI tract disease.
• IBD • Identify and treat underlying contributory • Decreased intestinal motility is probably
• Intestinal lymphoma disorders (e.g., EPI, IBD). an important cause of ARD; in addition
• EPI • Fenbendazole 50 mg/kg PO q 24h for to GI tract disease, consider endocrine
• Intestinal obstruction: stricture, intussuscep- 3-5 days should be considered for occult (hypothyroidism, diabetes mellitus, hypo-
tion, neoplasia, foreign body (may cause parasitism before antibiotic therapy. adrenocorticism) and neurologic causes.
secondary ARD) • Unless specifically directed by fecal culture, • German shepherd dogs are likely predisposed
• Motility disorders antibiotic choices include to ARD due to EPI (p. 317).
• Surgical causes: bypass procedures, ileocolic ○ Tylosin 10-25 mg/kg PO q 12h for up • Enzyme replacement for EPI may not
valve resection to 6 weeks, or be efficacious until antibiotic therapy is
○ Metronidazole 10-15 mg/kg PO q 12h instituted.
Initial Database for up to 2 weeks, or • Histiocytic ulcerative colitis (large-bowel
• Fecal flotation and direct smear to rule out ○ Enrofloxacin 5-10 mg/kg PO q 24h (only disease) is an antibiotic-responsive diar-
parasites for E. coli–associated histiocytic ulcerative rhea in dogs suspected to be secondary
• Results of CBC, biochemistry panel, and colitis) to invasive and adherent E. coli strains
urinalysis are usually nonspecific; hypo- • Parenteral or oral B 12 supplementation to (p. 395).
proteinemia may suggest protein-losing normalize serum levels (p. 183)
enteropathy. • Low-fat, highly digestible diet Technician Tips
• Abdominal radiography and/or ultrasonogra- • Prebiotic therapy: fructo-oligosaccharides • Long-term antibiosis may be required
phy may show underlying obstructive disease may stimulate normal microbiota for therapuetic success, but recent data
or neoplasia. • Dietary fiber: increase, decrease, or change suggest that chronic antibiotic use may be
in type (soluble vs. insoluble) to alter a risk factor for various metabolic disorders
Advanced or Confirmatory Testing microbiota due to the negative impacts on colonic
• Increased serum folate concentrations or microbiota.
decreased serum cobalamin concentrations Chronic Treatment • Slow tapering of the tylosin dose over time
lack sensitivity and specificity. Specificity • Some animals have recurrent signs when anti- appears to reduce relapse rate of clinical
increases if serum levels of both vitamins biotic treatment ends. Long-term, low-dose signs.
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