SHIC-funded Research Will Help Investigate PCV3 through Improved Diagnostics

January 24, 2018 — Paul Sundberg

PCV3 is on the radar of Swine Health Information Center (SHIC) as a potential emerging disease, with recognition that more work needs to be done to understand its role in disease syndromes. Newly released research sponsored by SHIC gives the industry the ability to detect and differentiate the majority of field strains of PCV3 and PCV2. With these diagnostic capabilities now available, SHIC encourages vigilance and diagnostics in cases of unresolved Porcine Dermatitis Nephropathy Syndrome (PDNS) and other clinical signs to help better understand the incidence of PCV3.

With lessons learned from PED in mind, making sure the pork industry is ready to diagnose emerging diseases is a key part of SHIC's priorities. Post assessment of diagnostic readiness for PCV3, research priorities included developing the means to detect and differentiate PCV3 and understanding better the virus' ability to mutate. A research grant, to that end, was given to Jianfa Bai, Ph.D., Director of Molecular Research and Development at Kansas State Veterinary Diagnostic Laboratory. Dr. Bai's laboratory has developed over 50 molecular diagnostic assays or DNA sequencing procedures to validate and improve molecular diagnostic methods for pathogens. His team also specializes in exploring new technologies to increase throughput capabilities in labs.

Prior to this study, there were a limited number of PCV3 genome sequences available but, what was there, showed the PCV3 genome shares little similarity to PCV2. The first objective of the SHIC-sponsored study was to develop a multiplex real-time PCR assay that can detect and differentiate the majority of the field strains of PCV3 and PCV2. The second study objective was to sequence at least 50 PCV3 genomes to study the genetic diversity, understand more about PCV3 genetic mutations, and to guide existing assays to ensure diagnostic coverage. Making sure all genetic sequences were analyzed was essential to ensure the assay could cover all known sequences.

Outcome highlights:

1. PCR ASSAYS DEVELOPED THAT SIGNIFICANTLY IMPROVE DETECTION OF PCV2 STRAINS
   • The team developed two sets of tests that in combination can detect 98.9% of PCV2 strains including PCV2a, 2b, 2c, 2d and 2e genotypes.
2. PCR ASSAY DEVELOPED TO COVER KNOWN SEQUENCES OF PCV3
   • When Bai started this study, 32 sequences of PCV3 were available. He developed an assay that could cover these 32 at a 100% rate. However, when more samples became available from the public database, as well as from Kansas, there were mismatches. Bai's team developed a test to figure these out. With the second test, over 89 sequences of PCV3 were uncovered. The new test developed has 100% coverage of these.
3. PCV3 MUTATION RATE UNCOVERED SUGGESTING VIGILANCE NECESSARY TO MAINTAIN NEW ASSAY'S 100% COVERAGE CAPABILITIES
   • Regarding the virus' ability to change, the largest genetic mutation rate for PCV3 was found to be 3.2% over the past 2 years. Monitoring the evolution of PCV3 may need to occur to keep diagnostic assays up to date.

Importantly, thanks to SHIC-sponsored research, veterinarians' diagnosticians can now detect and differentiate PCV3. With this ability, comes encouragement from SHIC to figure out if unexpected cases of PDNS and other clinical signs may be tied to PCV3, so we can better understand impact and prevalence to assess if this is an emerging disease. Further studies on PCV3 are needed to look at the effectiveness of existing PCV2 vaccines to cover PCV3, testing of PCV3 vaccines and U.S. prevalence.

For incidents of high or ongoing morbidity or mortality where an etiology is either not identified or there is a strong suspicion that the identified etiology is not the likely cause of the outbreak, SHIC offers support for the need for further diagnostic workup to identify newly introduced or emerging swine diseases. Read more at https://www.swinehealth.org/shic-support-for-diagnostic-fees/

Funded by America's pork producers to protect and enhance the health of the US swine herd, the Swine Health Information Center focuses its efforts on prevention, preparedness, and response. As a conduit of information and research, SHIC encourages sharing of its publications and research for the benefit of swine health. Forward, reprint, and quote SHIC material freely. For more information, visit http://www.swinehealth.org or contact Dr. Paul Sundberg at psundberg@swinehealth.org.

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Paul Sundberg, Executive Director, Swine Health Information Center