With the discovery that oral fluids from pigs contain the same diagnostic treasures as blood samples, producers and veterinarians have turned to rope testing as a convenient way to sample groups of pigs. Tests are now available to detect both PRRS virus (PCR) and PRRS antibody (ELISA) in oral fluids.
At the recent PRRS CAP Conference in Des Moines, Dr. Jeff Zimmerman from Iowa State University reported on the added benefits of using oral fluids as a noninvasive method for PRRSV surveillance. He explained how a rope sample from a pen of pigs is better than a pooled blood sample of randomly selected pigs because pooled samples are diluted and always result in loss of information, regardless of test sensitivity.
In preliminary studies, Zimmerman and colleagues found:
When 20 percent of the pigs in a pen are infected with PRRSV, there is a 70 percent chance of finding a positive result with rope testing.
When 36 percent of the pigs are infected, there is nearly a 100 percent chance of detection.
In comparison, the chance of a single blood sample from each of these pens detecting a positive result would be 20 percent or 36 percent, respectively.
In a study published in The Veterinary Journal, researchers observed pig behavior in pens with cotton ropes and found that 75 percent of the pigs in a pen chewed on a single rope within twenty minutes of placement. If two ropes were placed in a single pen, 90 percent of the pigs chewed on at least one rope within twenty minutes.
Additional work at ISU has found that mucin, a component of oral fluids in all species, binds or inactivates virus over time. Therefore it is important to submit chilled samples soon after collection in order to obtain the best results. If samples can be submitted quickly, refrigeration of oral fluids is preferable to freezing because the freeze-thaw cycle multiples the negative effects of mucin.
Commercial rope test kits are available through veterinarians. For information on rope testing your herd or the Voluntary Regional PRRS Elimination Project, contact project coordinator Dave Wright at (763) 242-7535 or wright2us@aol.com.
By:
Dave Wright, DVM
University of Minnesota
Email: wright2us@aol.com
Source: mnpork