Source: Swine Health Information Center
Preliminary results from research sponsored by the Swine Health Information Center (SHIC) shows statistically significant correlation between PCV3 and the clinical sign of fetal death as well as histological lesions of myocarditis, vasculitis of the heart, and vasculitis of the spleen. A newly developed and validated mqPCR assay enables performance of rapid, sensitive, and specific detection and differentiation of PCV3 and PCV2 strains with high strain coverage in clinical samples.
PCV2 is a major pathogen. PCV3 has been detected in pigs with symptoms of porcine dermatitis and nephropathy syndrome, porcine respiratory disease complex, enteritis, and reproductive failure. It has been hard to discern correlation of PCV3 with disease lesions for some veterinarians and pathologist, especially when the industry acknowledges that PCV2 has evolved which makes it more difficult to identify. Much of the confusion lies in the inability to definitively discern what is the cause if one or both differentials are difficult to identify.
Today, in the general swine veterinary population, experiences in the field generally influence whether a veterinarian believes that PCV3 causes disease. This ongoing discussion yields a sense of déjà vu for swine veterinarians who lived through similar doubts and conversations with PCV2 back in the early to mid-2000s.
For practitioners to have more confidence in determining cause and correlation, more proof of correlation is needed of PCV3 with lesions as well as better diagnostic tools. That's where Albert Rovira from the University of Minnesota and Yin Wang, a member of Jianfa Bai's team from Kansas State University, report SHIC sponsored research results to answer some of these questions.
Rovira's research mined the diagnostic data from over 817 pigs in the University of Minnesota Veterinary Diagnostic Laboratory database to identify associations between the presence of PCV3 and its viral load and specific lesions and clinical conditions. They started to analyze the data to find associations between the presence and load of PCV3 and certain clinical signs, lesions, and coinfections. Preliminary analysis shows statistically significant correlations with fetal death, myocarditis, and vasculitis of the heart and spleen. Wang has worked to evaluate tools that help differentiate clinical symptoms caused by the two circoviruses. Specifically, the objective of the team's recent study was to develop a multiplex quantitative real-time PCR (mqPCR) assay to rapidly detect and differentiate the two important circoviruses, with significantly improved diagnostic coverage to current field strains.
Considering that the PCV2 assays built many years ago might not be covering all field strains, there was a need to develop a mqPCR assay that was based on the most current sequencing data, capable of discerning PCV2 and PCV3, and contained a high diagnostic coverage to field strains.
The diagnostic sensitivity of the assay is promising. Sixty selected PCV3 positive samples with Ct values from 18 to 35 were verified indicating 100% diagnostic sensitivity. For PCV2, 53 of 56 positive samples were verified. Tests showed that multiplexing is not reducing the assay's sensitivity. Results also showed that the assay specifically detected PCV2 and PCV3 positive samples without cross deletion and no signal was generated from samples that were positive to other common porcine viruses.
Other benefits are that this assay has higher strain coverages: 97.9% for PCV3 and 99.1% for PCV2. Also, using two overlapping targets for a given virus increases field strain coverage and helps to detect strains with additional mutations. Viral targets were detected from serum, oral fluid, feces, intestines, and tonsil.
Of samples surveyed, the PCV3 positive rate was 30.1% which was close to double the PCV2 positive rate of 16.7%. Researchers speculate that vaccination has reduced prevalence of PCV2 and plan to keep monitoring the field samples to see if this prevalence data holds true.