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Viral Disease - Canine Parvovirus

Definition

CPV causes acute contagious enteritis with a high morbidity and mortality in immunologically naive dogs.

Rarely, myocardial disease results from perinatal infection.

Cause

Canine parvovirus-2

SS-DNA virus of the family Parvoviridae

CPV-2b: most common disease-causing strain in the United States

CPV-2: distinct from CPV-1 (including disease manifestations)

Epidemiological findings

This highly contagious virus is shed primarily in the feces of infected and recovering animals.

Fomites are a more common source of exposure than direct contact with feces, and CPV-2 persists in the environment.

Incidence is higher in summer and late fall.

Immunologically naive animals (young puppies) are the most susceptible to CPV-2 infection; however,older, immunocompromised animals are also at risk.

Reported breed predispositions include the rottweiler, American pit bull terrier, Doberman pinscher, and German shepherd dog

Pathogenesis

After oronasal exposure (primary route) initial replication occurs in local lymphoid tissues, with subsequent viremia in 2 to 5 days.

Rapidly dividing tissues (e.g., intestinal crypt cells, bone marrow leukocyte precursors) are preferentially infected; dissemination to the lungs, kidneys, and myocardium is possible.

Infection of intestinal crypt cells and leukocyte precursors leads to classic manifestations of the disease.

  • » Crypt necrosis and villous blunting with secondary diarrhea
  • » Neutropenia with increased susceptibility to secondary bacterial infections and sepsis

In utero or perinatal infections cause myocardial disease (rare) if insuffi cient maternal antibody is present.

Clinical Signs

Enteritis

  • » Initially anorexia, depression, vomiting, fever
  • » Diarrhea, often hemorrhagic
  • » Dehydration with inadequate fl uid intake and losses via the GI tract
  • » Hypovolemic or endotoxic shock in severely affected dogs or progressive disease

Myocarditis

  • » Entire litter affected (rare)
  • » Sudden death or congestive heart failure

Diagnosis

General diagnostic testing

  • » Hematological findings

    • » Neutropenia is a classic finding.
    • » Lymphopenia, anemia, and thrombocytopenia are also possible.

  • » Serum biochemistry: panhypoproteinemia and electrolyte imbalances possible
  • » Abdominal imaging

    • » Nonspecific findings suggestive of enteritis
    • » Used to rule out other intestinal diseases, especially intestinal intussusception

CPV-2-specific testing

  • » Fecal ELISA for viral antigen is the most commonly used test, but false positives (MLV vaccine 5 to 12 days previously) and false negatives (limited fecal shedding) occur
  • » Fecal or intestinal EM, fecal PCR, and virus isolation are rarely used clinically.
  • » Serological testing is rarely performed, but a fourfold rise in convalescent IgG titers is diagnostic.
  • » Histological findings include intestinal crypt necrosis or non suppurative myocarditis (rare).

Differential Diagnosis

GI signs:

CCV, bacterial enteritis, parasites, CDV, CHV, toxins, foreign body, intussusception, metabolic diseases

Congestive heart failure:

congenital heart disease, protozoal diseases, non-cardiogenic pulmonary edema (e.g., electrocution, neurological disease, trauma)

Treatment

Antiviral therapy is not necessarily required.

  • » Interferon omega 2.5 million units/kg IV SID for 3 consecutive days (de Mari et al., 2003) may be tried.
  • » Oseltamivir phosphate (Tamiflu) is a neuraminidase inhibitor used for influenza virus, and may be given for parvoviral enteritis at 2 mg/kg PO BID for 5 days (anecdotal).

GI therapy is outlined in Box 112-1.

  • » Adjunctive therapy involves hyperimmune plasma transfusions (1.1 to 2.2 mL/kg IV) from recovered dogs
  • » Empirical deworming is used to eliminate concurrent intestinal parasites.
  • » Treatment with recombinant human granulocyte colony-stimulating factor (G-CSF) is not beneficial
  • » CPV-2 infection may be fatal, but many animals fully recover.

Myocardial disease is extremely difficult to treat.

  • » Because the disease is rapidly progressive and fatal, therapeutic intervention is rarely attempted.
  • » Treat congestive heart failure in survivors.

Monitoring and Prevention

Quarantine unvaccinated animals.

Passive immunity is important in neonates.

  • » Maternal Ab titers >1:80 (hemagglutination-inhibition) are protective
  • » Maternal Ab typically protects for 6 to 12 weeks and may interfere with vaccination responses up to 18 weeks of age (Coyne, 2000).

Good acquired immunity is achieved through vaccination.

  • » High-titer potentiated MLV CPV-2 vaccines are preferred.

    • » They induce protective immunity in puppies when maternal Ab is present
    • » Annual to triennial booster vaccines are recommended.

  • » Low-titer, MLV CPV-2 vaccines do not always protect puppies with high maternal Ab levels, even at weeks of age, but the vaccines do provide adequate protection for older puppies and adults.

Following natural infection, recovered animals have long lasting immunity.

The virus is resistant to most disinfectants.


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