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Managing patients with parvoviral enteritis (Proceedings)

May 01, 2011

Puppies and young dogs - parvovirus enteritis

Disease caused by parvovirus in dogs (destruction of intestinal crypt epithelium, lymphocyte depletion, neutropenia) is generally more severe than that caused by coronavirus (destruction of intestinal villi). Coronavirus enteritis is often characterized by mild and self-limiting clinical signs. Intestinal mucosal injury due to parvovirus is more extensive, involving both crypt and villous epithelium. A combination of secretory and malabsorptive diarrhea results. Sepsis occurs commonly in dogs with parvovirus due to absorption of preformed bacterial toxins and intact bacteria across the damaged intestinal epithelium. Bacteremia is more likely to occur in severely leukopenic animals. Sepsis occurs infrequently in dogs with coronavirus enteritis.

Treatment of acute infectious diarrhea in dogs (e.g., parvovirus enteritis)

Fluid therapy

Fluid replacement is one of the most important treatments for patients suffering from vomiting and diarrhea. Rate and route varies with each patient, but patients with hemorrhagic gastroenteropathy are often dehydrated at presentation and strong consideration must be given to intravenous fluid therapy. Restoration of an effective circulating blood volume is of primary importance in the management of hypovolemic and septic shock. Subcutaneous fluid administration provides slow, unreliable volume replacement, may induce hypothermia, and occasionally results in the formation of subcutaneous abscesses.

Initially, a buffered crystalloid solution such as lactated Ringer's or Normosol-R should be given, followed by fluids with glucose added (lactated Ringer's or Normosol-R with 5% dextrose) when dehydration becomes less severe (5-6%). Both lactated Ringer's and Normosol-R are mildly alkalinizing and may be beneficial in patients with metabolic acidosis, especially in animals with severe diarrhea. The buffer sources in Normosol-R are acetate and gluconate. An advantage of acetate and gluconate is that they do not require hepatic metabolism and they do not contribute to lactate levels.

The calculation of fluid requirements should be the sum total of: 1)daily maintenance requirements, 2)deficits due to dehydration, and 3)continued (contemporary) losses (vomiting and diarrhea). Generally, the average adult dog requires a maintenance volume of approximately 30 ml/lb body weight per day. Estimation of dehydration is at best crude, but is derived from an accurate history, physical examination, and laboratory data. Once calculated only 75-80% of this volume is replaced the first twenty-four hours with the remainder given the second day.

If the animal is in critical condition, a "shock dose" of fluids is often given the first hour and is roughly up to 40 ml/lb (in the first one to two hours).

Antibiotic therapy

Most cases of simple vomiting and diarrhea do not warrant any antibiotic therapy. However, patients with hemorrhagic gastroenteropathies should be given antibiotics because the severe intestinal mucosal inflammatory changes which occur allow the normal intestinal microflora to invade the intestinal mucosa and lead to septicemia. Antibiotics are specifically given to eliminate microflora invading the mucosa, to eliminate microflora causing septicemia, and to eliminate pathogens that have invaded.

Bacteria invading the mucosa to produce bacteremia are members of the normal intestinal microflora. Antibiotic treatment is directed against both groups of bacteria, the aerobes (especially Escherichia coli) and anaerobes (especially Bacteroides and Clostridium of bowel origin). The important source of the bacteremia is the anaerobes (outnumber the aerobes in the colon by 1,000 to 1). Penicillin is the most effective antibiotic against anaerobes invading from the colon.

If patients with hemorrhagic gastroenteropathy are only mildly ill, and have an adequate number of white blood cells, penicillins are a good initial choice. Amoxicillin (10 mg/lb IM or SC every 12 hours) or ampicillin provide adequate coverage. Cephalosporins also provide good coverage for both aerobic and anaerobic bacteria (10 mg/lb IV every 8 hours). Antibiotics should not be administered subcutaneously in dehydrated animals because the rate of absorption will be delayed.. Aminoglycosides can cause acute renal tubular necrosis. Maintenance of normal blood volume is essential when using aminoglycoside antibiotics.