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Canine Parvovirus: Profile of a Killer

September 20, 2009 By: Dr. K Category: Opinion

parvovirusCanine parvovirus (CPV) is a highly contagious virus affecting puppies and unvaccinated young dogs in the United States.  Since evolving via a series of viral mutations in the early 1980’s, CPV has maintained a mortality rate of up to 30%. The advent of the parvovirus vaccine has dramatically decreased the incidence of disease. CPV specifically targets intestinal cells thus causing severe diarrhea, vomiting, dehydration, and weight loss.  Infections also cause bloodwork abnormalities including leukopenia with a neutropenia (low white blood cell counts). This makes infected dogs more susceptible to sepsis and subsequent cardiovascular collapse and hypoglycemia. Other complications include hypovolemic shock, disseminated intravascular coagulopathy (DIC), and acute respiratory distress syndrome. Dr. Linda Schell, DVM, DACVIM notes that “in experimentally affected dogs, mortality without treatment has been reported as high as 91%. However, with prompt recognition of dogs infected with CPV-2, and aggressive in-hospital supportive therapy of severely affected puppies, survival rates may approach 80-95%. ” At risk breeds include all dogs but Rottweilers, Dobermans, Pit Bulls, Labradors, and German Shepherd Dogs are most susceptible.

Clinical Presentation

  • Gastrointestinal – vomiting, diarrhea, inappetance, weight loss
  • Hematologic – immunosuppression secondary to depletion of lymphoid tissue, bone marrow
  • Cardiovascular – hypovolemic shock with circulatory collapse (poor pulses, pale mucous membranes, poor tissue perfusion), hypercoagulability, DIC, rarely viral myocarditis
  • Other clinical signs involving liver, kidneys, and central nervous system secondary to sepsis, dehydration, and endotoxemia

Diagnosis

  • Fecal ELISA, also known as the Parvo Snap Test, tests for parvoviral antigens in the feces. False negatives occur due to short period of viral shedding. False positives can occur if the dog has been vaccinated within the past 5-15 days although research from Idexx, makers of the snap test,  has indicated that 0 of 64 recently vaccinated beagles tested falsely positive.
  • Other tests include: virus isolation, PCR, electron microscopy, culture, and serologic studies for hemagglutination inhibition. These tests are not commonly performed.

Incubation/Infectious Periods

  • Virus can be found in blood 3-5 days following infection
  • Incubation period is 7-14 days, though animals can shed virus in feces prior to any clinical signs
  • Fecal shedding can occur for up to 10 days post-viremia
  • Virus is stable in environment for months to two years in the environment after fecal shedding but can be destroyed by a 1:30 bleach solution (See Environmental Decontamination below)

Treatment
Depending on severity of disease, any number of treatments may be necessary and include:

  • Intravenous fluid therapy including colloidal fluids and potassium/destrose supplementation
  • Blood transfusions for severely anemic animals
  • Antibiotic therapy to combat secondary bacterial infections
  • Antiemetics like maropitant, metocloprimide, and odansetron
  • Gastrointestinal protective agents like famotidine, sucralfate
  • Dr. Schell provides information on Tamiflu (oseltamivir phosphate): “Tamiflu is a neuraminidase inhibitor. Neuraminidase is a protein found on the surface membrane of many viruses that allows the virus to bud from the host cell to infect other cells; it is required for the virus to pass through mucous to reach non-infected cells. Unfortunately, the CPV (and the canine distemper virus) does not have neuraminidase. However, it has been theorized that the improvement seen in Tamiflu-treated CPV cases is because of inhibition of neuraminidase activity related to inflammation and bacteria (secondary sepsis). Tamiflu’s use is controversial for several reasons. By the time symptoms of CPV infection appear, the disease may be too far along for the drug to be useful. There are no proof of efficacy studies. It is expensive. Appropriate dosing is unknown. Finally widespread use of it in veterinary medicine could result in development of resistance mechanisms that would make this drug less useful in the event of a human influenza pandemic.”

Recovery

  • Recovery is dependent on when the disease is diagnosed and how aggressively it is treated.
  • Dogs who recover from CPV have immunity from reinfection for years or even their lifetime.

Prevention

  • Ensure your new puppy has been vaccinated appropriately against CPV. Talk to your veterinarian to find out if your dog has been adequately protected.
  • Keep your puppy away from unfamiliar dogs and out of dog parks until it is fully vaccinated.

Check out this great article on Environmental Decontamination

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