Asfarviridae

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VIRUSES



Introduction

Asfarviridae receives it's name from African Swine Fever virus, which is derived from any of this family of viruses. ASF is a serious exotic virus that should not be confused with Classical Swine Fever.

Morphology

  • Large, enveloped, icosahedral, cytoplasmic DNA virus

Virulence and Pathogenesis

  • Infects either upper respiratory tract or skin via ticks
  • Enters bloodstream in monocytes
  • Reaches viscera and bone marrow within days
  • Induces a clotting defect and hemolysis in red blood cells
  • Also affects lymphocytes:
    • Infects Th cells and causes them not to produce B-stimulating cytokines
    • Antigen-stimulated B-cells undergo apoptosis rather than producing antibody
  • General cell signal transduction is blocked, decreasing non-specific immunity

Acute Virus (Africa)

  • Clinical Signs:
    • Nasal discharge, diarrhoea, reddening of the skin
  • Death within 7 days
  • PM: widespread internal hemorrhage

Subacute Virus (Europe)

  • PM: Petechial hemorrhages may be seen under kidney capsule
  • Mortality: 30-70%
  • Survivors may lose body condition, have skin ulcers and joint swelling

Epidemiology

  • Can persist on infected premises for months
  • Subacute recovered pigs become antibody-positive carriers
  • Transfer:
    • Africa: vertical transfer between soft ticks
    • Europe/Africa: direct contact with carrier pigs, aerosol, infected swill, etc.

Diagnosis

Control

  • No vaccine is available

Prevention:

  • Boiling swill
  • Isolation of sick pigs, domestic pigs from wild pigs
  • Keep pigs on concrete, not soil (to lessen tick contact)