canine parvo viral treatment

Canine Parvovirus Enteritis
by Dr. Randy Wetzel

Canine parvovirus (CPV) enteritis is a common cause of acute, severe gastroenteritis in young dogs. Dogs at greatest risk are less than 6 months of age and either unvaccinated or incompletely vaccinated for canine parvovirus. Dogs vaccinated with over-the-counter vaccines also appear to have a higher incidence of parvovirus likely due to ineffective vaccine or improper use. Early clinical signs of parvovirus enteritis include anorexia, lethargy, diarrhea and vomiting.

Parvovirus enteritis has a survival rate of 85-90% with aggressive treatment and recovery generally occurs in 3-7 days. For patients who do not receive aggressive and appropriate treatment, the mortality rates increase substantially. Death is generally due to sepsis and/or dehydration. Correcting dehydration and electrolyte imbalances and reducing further fluid loss is critical to successfully managing these patients. For most patients this requires hospitalization on IV fluids, IV antibiotics, antiemetics, and GI protectants as the mainstay of treatment. Once a patient is hydrated, we find synthetic colloids such as Hetastarch (20ml/kg/day CRI) beneficial in replacing intravascular volume, maintaining hydration and managing shock. Synthetic colloids are excellent in their ability to increase COP which is often a concern in patients with hypoalbuminemia and increased capillary permeability as is often the case with so many CPV enteritis patients. Use of synthetic colloids generally permits you to decrease crystalloid fluid rates by 40-60%. Natural colloids such as fresh frozen plasma (FFP) or fresh whole blood (FWB) may be beneficial for anemic patients or those needing further immune support. In addition to providing oncotic components, both whole blood and plasma contain antibodies and serum protease inhibitors which may be beneficial in neutralizing circulating virus and controlling the systemic inflammatory response associated with the disease.

Parvovirus patients are often suffering from bone marrow suppression and their immune systems are overwhelmed by the viral infection making them at high risk of sepsis. We use broad-spectrum antibiotics such as Ampicillin, 22mg/kg IV TID, and amikacin 10mg/kg, IV TID, once the patient is hydrated. For patients with leukopenia, enrofloxacin at 5mg/kg IV BID diluted 1:1, is considered safe to use short term (3-5 days). Butorphanol 0.3mg/kg IV is recommended for abdominal pain, and a lower dose (0.15mg/kg) has been suggested in the medical management of patients suspected of having intussusception.

Tamilflu (oseltamivir phosphate) (1mg/kg PO BID for 5 days) used to treat influenza in people has anecdotally shown to be beneficial in treating CPV enteritis and thought to reduce viral replication.
Monitoring a complete blood count (CBC) is beneficial in evaluating a patient's condition. Patients with severe leukopenia raise concern about bone marrow suppression and risk of sepsis. I often find a poor correlation between the physical exam and attitude of the patient compared to the leukogram count. However, I do find positive correlation in patients with a low leukogram count and increased morbidity. These patients may benefit from more aggressive treatment immediately.

Treating patients with CPV enteritis is labor intensive and costly. A proper isolation ward and isolation protocol is important for reducing contamination to other patients. The profuse amount of vomiting and diarrhea makes proper isolation protocol challenging.

Parvovirus is shed in the feces by infected animals and this virus can remain stable in the environment for 7 months or longer. These viral particles can be transferred on the shoes, hands and clothes of people who then may expose an unprotected dog. It is very important to understand the ease of transmission and the fact that direct contact between the unprotected dog and the infected dog is not necessary for a pet to become exposed. Reducing risk of exposure is necessary, but it is vital to have pets inoculated with an effective vaccine at the appropriate time and properly administered. As an emergency clinician, I commonly see cases of parvovirus enteritis in patients who were vaccinated with vaccines attained through feed stores. The frequency at which this occurs raises a concern that the vaccines being used are ineffective or perhaps inappropriately administered. I commonly see mistakes in the timing of the vaccination when they are administered at home. It is important to understand the cycle of a puppy’s immune system with regard to maternal antibodies and duration of response to vaccination. Therefore initiating vaccination at 6 weeks of age by a veterinarian is strongly recommended.

References:
Rebecca Kirby, DVM, DACVIM, DACVECC
David Miller, BVSc, MMedVet
Douglass K. Macintire, DVM, MS, DACVIM, DACVECC
Alice M. Wolf, DVM, DACVIM, DABVP