Asfarviridae

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

• Mortalities with widespread hemorrhage, particularly in lymph nodes
• Test to distinguish from Classical Swine Fever and Porcine Circoviruses
• Immunofluorescence
• PCR

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)