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| GI InTerVenTIon: PATIenT wITh AcuTe DIArrheA Table 2. Differential Diagnosis of Acute Diarrhea SELF-LIMITING LIFE-THREATENING Dietary Indiscretion • chemicals and toxins • Diet change • Foreign material • Garbage or table scraps • Plants Bacteria • Campylobacter species • Clostridium difficile toxins A/B • Clostridium perfringens enterotoxin • enteropathogenic E coli • Salmonella species • Yersinia species Drugs • Antibiotics • cancer chemotherapeutics • copper chelators • corticosteroids • Digoxin • Magnesium antacids • nonsteroidal antiinflammatory drugs Systemic Diseases • Acute liver disease • Acute pancreatitis • Acute renal failure (leptospirosis) • canine distemper • hypoadrenocorticism • Salmon poisoning Parasites • coccidia, including Cryptosporidium species • Giardia • hookworms, roundworms, and whipworms Intestinal Obstruction • Foreign body • Intestinal accident • Intussusception Other • Acute colitis • Clostridium perfringens enterotoxin • coronavirus • Idiopathic Other • hemorrhagic gastroenteritis (see Box) • canine parvovirus and feline panleukopenia • Severe dietary indiscretion • Severe parasitism (hookworms and whipworms) Adapted, with permission, from Leib MS, Munroe we (eds): Practical Small Animal Internal Medicine. Philadelphia: wB Saunders, 1997, p 692. Hemorrhagic gastroenteritis (hGe) is a diarrheal syndrome of unknown etiology that has a predilection for small breed dogs; it has not been reported in cats. Speculation regarding pathogenesis includes type-1 hypersensitivity reaction to food components, cPe, and C difficile toxins A/B. hGe is distinctively characterized by peracute onset of bloody diarrhea and vomiting accompanied by marked hemoconcentration. Packed cell volume of an affected dog can reach 75% or higher within hours of onset of signs, yet total plasma protein often remains within reference range. Symptomatic therapy, primarily aggressive IV fluid therapy and gastroprotectants, results in marked clinical improvement within 24 to 48 hours. Antimicrobial therapy is usually administered, although in a recent study, clinical response was not improved in dogs that received antibiotics (amoxicillin/clavulanic acid).14 with appropriate therapy, mortality is low despite severity of signs. 22 Today's Veterinary Practice May/June 2013 confounds diagnosis, treatment decisions, and assessment of infection control and zoonotic risk (Table 3, page 25). Cytology. Microscopic examination of fresh feces has been used by some clinicians for presumptive diagnosis of disease by evaluating pathogen appearance. However, fecal cytology is now considered of no diagnostic utility for bacterial enteropathogen identification because: • These bacteria can be present in normal animals • Appearance does not differentiate between pathogenic strains and harmless commensal species • In the case of Clostridium perfringens, no studies have reported a correlation between presence or number of spores and signs of disease. Enterotoxin has received the most attention in relation to C perfringens, and some association has been found between the presence of C perfringens enterotoxin (CPE) and diarrhea in dogs.11 Intestinal Microbes. Intestinal microbes play a crucial role in maintenance of host health. They: • Act as a defending barrier against transient pathogens • Support the host in digestion and energy harvest from the diet • Stimulate the immune system • Provide nutritional support for enterocytes. The total microbial load in the intestine is estimated at 1012 to 1014 organisms, about 10× the number of host cells in the entire body. New technologies have enhanced our understanding of the microorganisms harbored by mammalian GI tracts. Massive parallel 16S rRNA gene pyrosequencing has provided the tool for molecular-phylogenetic characterization of the GI tract's complex microbial community.12 The gene content of these microbes is defined as the intestinal microbiome. There is mounting evidence that changes in microbial populations play an important role in pathogenesis of acute and chronic enteropathies of dogs. In a recent study, dogs with acute diarrhea, especially those with acute hemorrhagic diarrhea, had the most profound alterations in their fecal microbiome compared to healthy dogs, and observed changes differed between acute and chronic disease states.13 Recognition of fecal biome alterations (dysbiosis) in pets with various GI disorders opens the door to future studies that evaluate the ability of probiotics, prebiotics, antibiotics, and other therapies to restore the balance of bacterial flora. ACUTE DIARRHEA: HISTORY & PHYSICAL EXAMINATION Signalment and history often contain the information necessary to make a tentative diagnosis or help rank differential diagnoses (Tables 1 and 2).