Pig and piglet.

2020-21 Rapid Ag: Development of Diagnostic Strategies for Porcine Circovirus Type 3 Infections

April 4, 2019

Principal Leader

Sagar Goyal

Department

Veterinary Population Medicine

The Problem

Porcine circovirus type 3 (PCV3) was first discovered in 2016 in the US and has now been identified in many other countries. The virus is associated with systemic vasculitis/myocarditis, porcine dermatitis and nephropathy syndrome and reproductive disorders (Palinski et al. 2017; Phan et al. 2016). At the University of Minnesota Veterinary Diagnostic Laboratory (MVDL) we have been monitoring for the presence of PCV3 on a routine basis for the last two years using a polymerase chain reaction (PCR). In addition to the original cases, we have identified multiple other cases of abortion and systemic disease where PCV3 appears to be the cause of severe disease, based on the presence of the virus in large amounts within lesions, and the absence of other common swine pathogens. Evidence for the relevance of this newly discovered virus has been accumulating in the last two years and veterinarians and diagnosticians in the US are currently including PCV3 in their list of differentials in cases of reproductive and systemic disease. However, final proof of PCV3 being the cause of disease has not been demonstrated because the virus has not been isolated in vitro and therefore Koch’s postulates have not been fulfilled. Therefore, we propose to isolate the virus in vitro and to develop an experimental infection model to study the relevance and virulence of PCV3. In addition, we plan to generate a bank of samples that can be used for future studies on viral pathogenesis and vaccine development, and to develop an ELISA for the detection of anti-PCV3 antibody.

Background

At the MVDL, we tested 2,177 samples from 730 cases between February 2016 and January 2018; we detected PCV3 by PCR in 35% of the cases from 18 different U.S. states. The rate of positive samples was high for oral fluids and processing fluids (81%-89%), and lower for serum (23%) and tissue homogenates (18%). A majority of positive cases were subclinical in nature but in a few cases PCV3 was considered significant based on association with microscopic lesions (in some cases confirmed by in situ hybridization), low Ct values obtained by PCR and lack of other common pathogens. Of particular interest were cases of systemic vasculitis and myocarditis, and abortion cases in which PCV3 was the only pathogen detected.

Project Goals and Objectives:

  1. To develop methods for the in vitro culture of PCV3 (using samples from the field as well as from experimentally inoculated CDCD pigs and sows)

  2. To experimentally reproduce PCV3 infection in CDCD pigs and pregnant sows to understand disease pathogenesis and to obtain ‘clean’ samples for development of diagnostic assays including virus isolation in vitro

  3. To develop an enzyme-linked immunosorbent assay (ELISA) for the detection of anti-PCV3 antibodies.

References

  • Palinski et al. 2017. J Virol. 91:e01879-16
  • Phan et al. 2016. Virology J. 13:184; DOI 10.1186/s12985-016-0642-z
  • Dvorak et al. 2017. BMC Vet Res. 13(1):50. doi: 10.1186/s12917-017-0967-x
  • Arruda et al. 2016. PlosOne; DOI:10.1371/journal.pone.0150104