Kevin Vilaca from South West Ontario Veterinary Services,How Does The Pig Respond To PCV3?

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We have been following reports about novel Porcine Circovirus 3 (PCV3) for some time and the jury is still out on its importance to the industry. This virus is genetically distinct from but is related to PCV2. PCV3 has clearly been identified in some clinical cases associated with sow mortality, skin and kidney lesions consistent with porcine dermatitis and nephropathy syndrome (PDNS), reproductive failure and multisystemic inflammation. The mechanisms of disease as well as the broader clinical significance of PCV3 is still unclear. Researchers from University of Iowa and University of Minnesota cooperated in investigating the immunopathogenesis of PCV3 in Caesarian Derived/Colostrum Deprived (CD/CD) pigs. Four treatment groups of pigs , PCV3 (n=6), PCV3-KLH (n=6), control (n=3) and control-KLH (n=3), were included with PCV3-positive tissue homogenate (gc=3.38×1012 ml-1 and gc=1.04×1011 ml-1), confirmed by quantitative PCR (qPCR) and next-generation sequencing. ( Note: Keyhole limpet hemocyanin (KLH) is used extensively as a carrier protein in the production of antibodies for research, biotechnology and therapeutic applications.)

The researchers found the following:

  • No significant clinical signs were observed through the study.
  • Viremia was detected in both PCV3-inoculated groups from 3 days post-inoculation (p.i.) until the end of the study.
  • Nasal shedding was detected from 3 to 28 days p.i.
  • Faecal shedding was transient.
  • PCV3 induced an early (7 days p.i.) and sustained (42 days p.i.) IgG immune response.
  • No significant T-cell cell mediated immunity response was observed.
  • Histological evaluation demonstrated lesions consistent with multisystemic inflammation and perivasculitis consistent with previous reports of PCV3.
  • All tissues evaluated were positive by qPCR and virus replication was confirmed by positive in situ hybridization.

Take Home Messages:

  • PCV3 infection of CD/CD pigs resulted in a mild, multisystemic inflammatory response, prolonged viremia detectable for 42 days p.i., presence of IgG humoral antibody response and viral shedding in nasal secretions.
  • PCV3 infection of CD/CD pigs in this experiment did not produce any clinical signs. This is similar to the early work with PCV2 models where coinfection with diseases such as Porcine Parvovirus were required to create observable clinical signs.
  • This virus continues to look like the weaker cousin of PCV2 and although the virus is widespread it is only occasionally implicated as a cause of clinical disease. There is much more to learn about potential co-factors that may be involved in the severity of clinical disease.

Ref:   Gun Temeeyasen , Shay Lierman , Bailey L Arruda , Rodger Main  Fabio Vannucci , Luis G Gimenez-Lirola , Pablo E Piñeyro   Pathogenicity and immune response against porcine circovirus type 3 infection in caesarean-derived, colostrum-deprived pigs  J Gen Virol . 2020 Nov 18. doi: 10.1099/jgv.0.001502. Online ahead of print.