Porcine Circoviruses

Antigenicity

• Two serotypes:
  • PCV1 is harmless
  • PCV2 is virulent, causing:
    • Post-weaning Multisystemic Wasting Syndrome (PMWS) in young pigs
    • Porcine Dermatitis and Nephropathy Syndrome (PDNS) in older pigs

Pathogenesis

PMWS:

• Enlarged lymph nodes with lymphopenia as virus concentrates in germinal centers
• Typically strikes weaners (8-12 weeks old)
• Clinical signs:
  • Pale skin color
  • Jaundice
  • Enlarged lymph nodes and kidneys
  • Unthrifty appearance
  • Lameness
  • Respiratory disease
  • Occasional diarrhoea
• Large range of differentials, particularly Swine Fever, African Swine Fever, Pasteurella, and colisepticemia
• Mortalities can reach 40% in an outbreak; nationally range from 4-10% annually

PDNS:

• Can follow PMWS
• Seen in growers and finishers
• Presents as an immune-mediated necrotising vasculitis
• Extensive hemorrhages of kidneys and skin, especially in the scrotal region, accompanied by pyrexia

Epidemiology

• Poor immune response
• Transfer is orofecal and venereal
• PCV2 is the most important widespread porcine virus:
  • Detrimental losses to the industry
  • Predisposes to secondary infection
  • Easily misdiagnosed

Diagnosis

• Clinical signs
• Confirmed by PCR for PCV2 nucleic acid
• However, positives can show NO clinical signs
• Easily confused with Classical Swine Fever

Control

• No vaccines are available
• Antibiotics to prevent secondary infection
• Good ventilation, bio-security, and proper management
• Passive antibody can be used in dire circumstances:
  • Viral serum from an adult pig and be injected peritoneally into piglets to stimulate a high anitbody response
  • Must be done by a vet and only within a single herd

Postweaning multisystemic wasting syndrome (PMWS)

• Caused by a porcine circovirus alone or in combination with porcine parvovirus
• May cause mild interstitial pneumonia, failure of lungs to collpse on opening the thoracic cavity
• Microscopically: thickening of alveolar wall due to type 2 pneumocyte hyperplasia