Potential causes of acute diarrhea are listed in Table Causes of Acute Diarrhea, but whether a complete diagnosis is pursued and when therapy is instituted are clinical judgments. The diagnostic approach to acute diarrhea is discussed elsewhere.
Patients that are bright, alert, and not dehydrated may require no further investigation, because signs are often self-limiting. Further investigation of acute diarrhea is indicated under the following circumstances:
• The patient is dull or depressed, febrile, dehydrated, tachycardic or bradycardic or is having abdominal discomfort, melena, bloody mucoid stools, or frequent vomiting.
• Obvious physical abnormalities (e. g., intestinal masses, thickening, or plication) localize the problem to the small intestine, and diagnostic imaging, noninvasive biopsy, or surgery can define the cause.
• Systemic abnormalities are present, as defined by a minimum database and other clinicopathologic tests.
It is important that the patient be regularly re-evaluated to monitor the response to therapy and to detect any new abnormalities that may arise.
Causes of Acute Diarrhea
|Dietary||Hypersensitivity (allergy), intolerance, sudden diet change, food poisoning (poor quality, spoiled foods / bacterial)|
|Toxic||Food or other sources|
|Infectious||Parvovirus, coronavirus, paramyxovirus, adenovirus, may or may not be feline leukemia virus / FIV related; also Salmonella, Campylobacter, Clostridium spp. (?) and Escherichia coli (?)
Helminths; Coccidia, Ciardia spp.
FeLV, feline leukemia virus, FIV, feline immunodeficiency virus
Treatment of Acute Diarrhea
The initial management of acute diarrhea associated with systemic illness is symptomatic and supportive, and is commenced on the basis of clinical findings, in particular the presence of dehydration, while the results of the initial data base and further tests are pending.
Fluid therapy Oral fluid and electrolyte replacement therapy may be sufficient if acute diarrhea is associated with only mild or insignificant dehydration, and if vomiting is infrequent or absent, although its efficacy should still be monitored. However, when diarrhea is accompanied by significant vomiting or dehydration, parenteral fluids should be administered at a rate that replaces deficits, supplies maintenance needs and compensates for ongoing losses. Patients with marked hypovolemia require more aggressive support.
The type of fluid and requirement for potassium supplementation is best judged by performing a minimum data base and blood gas analysis. Parenteral fluids are usually best given intravenously. The intraosseous route can be used if venous access is unavailable, but subcutaneous administration of fluids is likely to be inadequate.
Diet Studies examining the role of diet in the treatment of acute diarrhea in dogs and cats are scarce. Current recommendations are based on common sense and anecdotal evidence Best practice generally is considered to be withholding food for 24 to 48 hours and then feeding a bland diet, given little and often, for 3 to 5 days. Thereafter the original diet is gradually reintroduced. In animals with no other significant clinical findings, this may be the only therapy required. Common choices of a bland, fat-restricted diet for dogs are boiled chicken or white fish or low-fat cottage cheese with boiled rice. Cats seem to have a lower tolerance to dietary starch and may benefit from a diet with a higher fat content. Little attention is paid to the overall nutritional adequacy of home-prepared bland diets when fed in the short term.
This dogma of intestinal rest has been challenged by studies that demonstrate that feeding human infants during diarrhea promotes recovery. The success of such feeding through diarrhea varies depending on the cause, with most benefit seen in secretory diarrhea. However, in dogs and cats, secretory diarrhea is less common, the increased volumes of diarrhea may be cosmetically unacceptable, and the frequently contemporaneous vomiting may preclude this approach. The inclusion of glutamine, a nutrient utilized preferentially by enterocytes, may also promote recovery and decrease bacterial translocatjon, although experimental proof of improved intestinal integrity in animals is lacking.
Theoretically, any intestinal disease may predispose the animal to the development of a food sensitivity, therefore feeding of a novel protein source during these periods may preclude the development of sensitivity to the staple diet. However, this concept of feeding of a sacrificial protein is supported only by circumstantial evidence.
Protectants and adsorbents Bismuth-subsalicylate, kaolin-pectin, montmorillonite, activated charcoal and magnesium, and aluminum and barium-containing products are often administered in acute diarrhea to bind bacteria and their toxins and to coat and protect the intestinal mucosa, but they may also have an antisecretory effect. Therapy for acute diarrhea with protectants, absorbents or motility modifying agents should not exceed 5 days.
Motility- and secretion-modifying agents Anticholinergics and opiates or opioids (loperamide, diphenoxylate) are frequently used for the symptomatic management of acute diarrhea, but anticholinergic agents can potentiate ileus and are not recommended. Opiate analgesics were thought to exert their effects by stimulating segmental motility, but they actually act mainly by decreasing intestinal secretion and promoting absorption and can be used in the short-term symptomatic management of acute diarrhea in dogs. They are contraindicated in cases involving obstruction or an infectious etiology.
Antimicrobial therapy Antimicrobials are indicated only in animals with a confirmed bacterial or protozoal infection, those in which a breach of intestinal barrier integrity is suspected from evidence of gastrointestinal bleeding, and hence in those at risk of sepsis. Leukopenia, neutrophilia, pyrexia, the presence of blood in the feces, and shock all are indications for prophylactic antibiotics in animals with diarrhea. Initial choices in these situations include ampicillin or a cephalosporin (effective against gram-positive and some gram-negative and anaerobic bacteria). If systemic translocation of enteric bacteria is suspected, antimicrobials effective against anaerobic organisms (e. g., metronidazole or clindamycin) and “difficult” gram-negative aerobes (e. g., an aminoglycoside or a fluoroquinolone) are indicated. Intravenous quinolones have been shown to reach therapeutic concentrations in the canine gut lumen and can be effective against enterococci, E. coli, and anaerobes. Oxytetracycline, tylosin, and metronidazole are suitable for the treatment of SIBO.
A four-quadrant, intravenous antibacterial regimen may be required if septicemia is likely, and suitable combinations would be a cephalosporin (or amoxicillin) or a fluoroquinolone (or amikacin) with metronidazole or clindamycin. However, aminoglycosides should not be given until the patient is volume-expanded.
Probiotics Traditionally, many practitioners have recommended feeding live yogurt as a way of repopulating the intestine with beneficial lactobacilli after an acute gastrointestinal upset. There is evidence in other species that probiotics do exert a positive effect on intestinal permeability and mucosal immune responses, although the effects may be species specific and present only while the probiotic is continuously administered. Probiotics are now available for use in dogs and cats, and emerging data exist to support their use.
Acute Diarrhea Induced by Diet, Drugs, or Toxins
Altered food intake, probably the most common cause of acute, self-limiting diarrhea in dogs, includes rapid diet change, dietary indiscretion, dietary intolerance, hypersensitivity, and food poisoning. Dietary hypersensitivity (food allergy) is probably rare. Ingestion of drugs (e. g., nonsteroidal anti-inflammatory drugs [NSAIDs] or antibacterials) or toxins (e. g., insecticides) also may cause vomiting and diarrhea. The history may allow an educated, presumptive diagnosis to be made. However, the exact cause often is never determined because the patient is not systemically unwell and responds to symptomatic therapy. The prognosis usually is excellent, and only if the diarrhea does not respond or the patient deteriorates is further investigation necessary.
There are numerous potential causes of bloody vomiting and diarrhea, but hemorrhagic gastroenteritis (HGE) is the name given to a syndrome characterized by acute hemorrhagic diarrhea accompanied by marked hemoconcentration. The cause of the syndrome is unknown. It may represent an intestinal type 1 hypersensitivity reaction or could be a consequence of C. perfringens enterotoxin production.
Clinical findings Dogs present with acute hemorrhagic diarrhea, with small breed dogs most frequently affected. Pyrexia is unusual, but vomiting, depression, and abdominal discomfort are common. The onset may be peracute and can be associated with marked fluid shifts into the small intestine, leading to severe hypovolemic shock even before signs of dehydration (e. g., decreased skin turgor) appear.
Diagnosis A presumptive diagnosis of hemorrhagic gastroenteritis can be made on the basis of appropriate clinical findings associated with a packed cell volume (PCV) of 55% to 60% or more. Total protein is often normal or not as high relative to the packed cell volume. probably because ot intestinal plasma loss. Radiographs may demonstrate ileus. The absence of leukopenia and the presence of marked hemoconcentration help distinguish hemorrhagic gastroenteritis from parvovirus. Positive fecal tests may support a diagnosis of clostridiosis, but direct evidence of small intestine infection is rarely obtained.
Treatment Intravenous fluids are essential in treating patients with hemorrhagic gastroenteritis. Some patients become hypoproteinemic, and plasma or colloid support may be required. Parenteral antibiotics are often administered because of potential clostridial infection and the high risk of sepsis. Clinical improvement is usually noted within a few hours, though the diarrhea may take several days to resolve. Close patient monitoring is essential; patients that have not responded within 24 hours should be re-evaluated for parvovirus, intussusception, or foreign objects. Once the patient is in the recovery phase, standard dietary therapy for acute diarrhea can be instigated. The prognosis for most animals with hemorrhagic gastroenteritis is good, but if hemorrhagic gastroenteritis is complicated by severe hypoproteinemia or sepsis, the prognosis is more guarded.
Infectious and Parasitic Causes of Acute Diarrhea
Diarrhea caused by infectious and parasitic agents is considered common in animals that are young, immunologically naive or immunocompromised, housed in large numbers, or housed in unsanitary conditions. Parvovirus, Giardia, Salmonella, and Campylobacter spp., and some helminths can be significant causes of diarrhea. The importance of coronavirus, C. perfringens, and E. coli as causes of diarrhea has yet to be defined. The zoonotic potential of many of these infections has not been clearly elucidated, but basic hygienic precautions should always be adopted. Specific small intestine infections are discussed below, but the reader is referred elsewhere for detailed information on other viruses such as paramyxoviruses, adenoviruses, feline leukemia, and immunodeficiency viruses, which also cause diarrhea but affect many other organ systems apart from the gastrointestinal tract.