Leading PRRS (porcine reproductive and respiratory syndrome) researcher Scott Dee, DVM, says the swine veterinary community needs an awakening and refocusing toward the goal of PRRS control and eradication.
“Veterinarians in North America and Europe possess some incredible diagnostic tools, such as molecular sequencing, that are unavailable in other countries,” states Dee, associate professor, University of Minnesota College of Veterinary Medicine.
Instead of using that technology to make much progress against PRRS, veterinarians, scientists and industry partners have taken to arguing amongst themselves. This needs to stop, and the industry needs to get on the same wavelength to identify the problems and develop solutions to PRRS issues, he asserts.
In short, the industry needs to redouble efforts to clean up PRRS, notes Dee. Realize, however, that there is no single blanket program that will work for PRRS eradication.
However, if there are multiple, diverse genetic strains of PRRS present in a herd, it's doubtful that gilt acclimation or vaccination will work. “Eradication may be the best solution,” he says.
In a talk at the Leman Swine Conference in Minneapolis, Dee outlined his concerns regarding the current status of PRRS eradication.
There is a great deal of confusion in the pork industry as to what exactly constitutes a PRRS negative herd. Breeding herds should not be considered negative based on production of negative pigs, particularly if 1-2% of groups test positive for PRRS on ELISA (enzyme-linked immunosorbent assay) test. What's needed is a global standard for a “PRRS-naïve” farm, a farm that has truly never been exposed to the PRRS virus since its inception.
There is no need for sale of PRRS-positive breeding stock in the pork industry today. The defeatist attitude that says there are two kinds of herds in the industry today — those that are going to get PRRS and those that have it — has done much to blunt progress of PRRS cleanup. Dee says producers don't have to live with PRRS. There is no need to buy the disease, either.
He declares: “Producers should always insist on PRRS-naïve semen and replacement stock, and have quarantine and testing programs in place to validate this status when new genetics arrive.”
Production of negative pigs from PRRS-positive sows is no guarantee of negative herd status.
There is no universal PRRS eradication program. As has been aptly demonstrated in the pseudorabies eradication campaign, multiple eradication schemes need to be developed and the correct one tailored to fit individual operations. Veterinarians should assess all options to select the correct means of eliminating PRRS from a particular farm. The strategy selected should be based on the level of risk that the veterinarian and the producer are willing to accept, capital available and if there are alternate sites.
Rollover programs hold promise but need further evaluation. Test and removal programs work very well for unvaccinated farms. Depopulation-repopulation remains a viable option; however, reinfection is a major risk factor to consider, says Dee.
Avoid drawing conclusive findings from limited data on sentinel animals. Negative status means simply that the tested animals have not been infected. It does not indicate anything regarding the carrier status of the herd. Testing isolated gilt sentinels can produce “false negative” readings. Remember that breeding stock can carry PRRS virus and not shed.
“Therefore, based on data from our sow model and shedding experiments, I believe the best solution is to use PRRS-naïve, vasectomized boars as sentinels, housing them adjacent to pens of weaned sows, allowing for nose-to-nose contact on a daily basis.” This recommendation is based on an increasing number of cases where gilt sentinels housed in gestation have remained negative, yet sentinel boars in contact with weaned sows in the breeding area have become positive (seroconverted) for the virus.
Quibbling and arguing amongst veterinarians has reduced the stature of the profession. What's needed is unification so we can speak with a common voice regarding PRRS, he points out.
“Only if we work together will we win the war against this very clever virus,” concludes Dee.