Diagnostic sampling strategies and classification of breeding herds for PRRS virus

1. Diagnostic sampling strategies and classification of breeding herds for PRRS virus Pilot training school in PRRS diagnostics, 2012 Zagreb, Croatia Dr. Derald Holtkamp September 24, 2012

2. Objective • Provide a herd classification system for describing the PRRSV status of herds, based upon a set of definitions that reflect the biology and ecology of PRRS virus • Why? • Required for implementation of regional and national efforts towards PRRSV control and elimination • Necessary to facilitate communication between veterinarians, swine producers, genetic companies, and other industry participants

3. Background • A definitions committee was formed to develop a herd classification system for describing the PRRS virus status of herds in July of 2009 • The committee was formed jointly by • American Association of Swine Veterinarians (AASV) • United States Department of Agriculture (USDA) PRRS-CAP

4. Background • Committee was chaired by Dr. Bob Morrison and composed of researchers and veterinarians from private practice, industry, and representatives from the American Association of Swine Veterinarians (AASV) and National Pork Board (NPB) • Drs. Dyneah Augsburger, Lisa Becton, Steve Henry, Derald Holtkamp, Dale Polson, Max Rodibaugh, Bob Rowland, Harry Snelson, Barb Straw, Montse Torremorell, Paul Yeske, Jeff Zimmerman (in alphabetical order) • Input was also received from the AASV PRRS Task Force

5. Background • The herd classification system proposed by the committee was approved by the AASV Board of Directors on March 9, 2010 • A recommendation from the AASV PRRS Task force was made to the Board to approve the herd classification system • A manuscript describing the herd classification system and related terminology has been published in the Journal of Swine Health and Production (JSHAP) as a peer reviewed commentary Holtkamp D.J., Polson D.D., Torremorell M. and committee members Morrison B. (chair), Classen D.M., Becton L., Henry S., Rodibaugh M.T., Rowland R.R., Snelson H., Straw B., Yeske P., Zimmerman J. 2011. Terminology for classifying swine herds by PRRS virus status. J. Swine Health Prod. 19:1 44-56.

6. Basis for classification of a herd • The herd classification system is based upon the shedding and exposure status of the herd • Shedding status is negative, uncertain or positive • Exposure (current or past infection) status is negative or positive

7. Diagnostic evidence is based upon periodic herd tests • Rely upon PCR and ELISA • For the purpose of establishing a negative or uncertain shedding status and negative exposure status, no distinction is made between diagnostic results that are positive due to vaccine usage versus those due to wild-type virus exposure

8. What is an “uncertain” shedding status • An uncertain shedding status is used when diagnostic data is available to suggest shedding may have ceased in a herd but without sufficient confidence to support a negative shedding status • Lack of power in the sampling and testing strategy! • An uncertain shedding status is considered transitory in the progress towards eliminating PRRS virus from an infected herd

9. Classification system for breeding herds Roman numerals were assigned to each category to emphasize that the status of herds must follow a specific order as they progress from Positive Unstable to Negative

10. Classification of breeding herds – IPositive shedding and exposure status

11. Classification of breeding herds – IIUncertain shedding and positive exposure status

12. Definition of elimination & when it begins

13. Classification of breeding herds – IIINegative shedding and positive exposure status

14. Classification of breeding herds - IV Negative shedding and exposure status For herds established Negative by “herd rollover”

15. Recommended protocol to assess PRRS virus status of Category II-A or II-B breeding herds • Trying to “rule out” that virus is circulating in the herd In other words we want to say with some confidence that PRRS virus is not being shed and transmitted to other pigs in the herd • Need to choose the right test • Need a sensitive test • Need to look in the right place • Need to carefully choose sample size and frequency • Prevalence is likely low as we are transitioning from Category I to II so we need sufficient sample size to find the small percentage of animals that may still be shedding virus

16. Recommended protocol to assess PRRS virus status of Category II-A or II-B breeding herds This is the test of choice

17. Recommended protocol to assess PRRS virus status of Category II-A or II-B breeding herds We don’t have unlimited money available for diagnostics

18. Recommended protocol to assess PRRS virus status of Category II-A or II-B breeding herds This is where we expect to find virus

19. Recommended protocol to assess PRRS virus status of Category II-A or II-B breeding herds How many and how frequently to sample

20. Recommended protocol to assess PRRS virus status of Category II-A or II-B breeding herds Will save money and time - OK?

21. Recommended protocol to assess PRRS virus status of Category II-A or II-B breeding herds How do we use the individual animal test results to make a diagnosis for the herd (ie. classification)?

22. Recommended protocol to assess PRRS virus status of Category III breeding herds

23. Recommended protocol to assess PRRS virus status of Category IV herds established by herd rollover

24. Acknowledgements • American Association of Swine Veterinarians (AASV) • PRRS-CAP, USDA NIFA Award 2008-55620-19132 • National Pork Board (NPB)