Farms.com, Canada
11-19-07
Update on PRRS
Porcine Reproductive and Respiratory Syndrome (PRRS) continues to affect pork production, but vaccine use is having a positive impact on producers’ bottom line, says Dr. Don Walter, DVM.
Dr. Walter serves as Technical Communications Manager for Boehringer
Ingelheim Vetmedica, Inc. He provided an update on PRRS in a recent conversation, covering four primary areas: the importance of protecting growfinish pigs; the occurrence of PRRS as a frequent co-infection in cases of
PCVAD (Porcine Circovirus Associated Disease); the increased severity of disease in such co-infections; and the benefits associated with vaccinating for both PRRS and PCV2 (circovirus) in such cases.
“It’s a surprisingly underappreciated fact that vaccination is very effective for controlling PRRS in growing pigs,” notes Dr. Walter. “Most people focus on the disease in sows, but it has been estimated by the National Pork Board and others that the disease in pigs accounts for 88% of the total losses to PRRS in the U.S. swine industry ($493M in pigs, $66M in the breeding herd). Therefore there is a tremendous amount of potential value to be harvested by controlling the disease in pigs
– vaccination is a very effective way to do that.”
Dr. Walter notes there have been 16 separate experimental studies recently summarized and reported, all showing significant vaccinal protection against a variety of PRRS virus isolates. “Consistent with the experimental observations,
Dr. John Waddell has published field observations in nursery pigs, and in this study, vaccine use helped bring average mortality rates down from greater than
9% to less than 3%,” says Dr. Walter.
“Another field study by Dr. Rick Tubbs further confirms these findings,” the veterinarian cont inues. “In this study, the average combined mortality and cull rate in finishing pigs decreased from greater than 11% to less than 6% postvaccination in a very large, continuous flow finishing site endemically infected with PRRS virus.”

Regarding co-infections with PCV2 in cases of PCVAD, PRRS is the most common co-infection, and Dr. Walter cited three examples:
1. An Iowa State University Veterinary Diagnostic Laboratory (ISUVDL) report from 2002, in which researchers looked at 484 cases of PCVAD diagnosed during 2000-2001: Over 50% of the cases had PRRS as a coinfection, and this was by far the most frequently reported co-infection.
2. Boehringer Ingelhiem’s own MAGIC program, which stands for Monitoring
Assignment for Global Insight into Circovirus-Associated Disease: This diagnostic investigation in 2006 studied 59 farms, and once more, PRRS was by far the most frequent co-infection. In fact, it was found on 72% of the farms.
3. Tanya Opriessnig gave a report at the recent 2007 Iowa State Swine Disease
Conference, confirming that the number of PCVAD cases and the number of
PRRS cases diagnosed in recent years at the ISUVDL have been very closely related.
Because of these high co-infection rates, Dr. Walter explains the critical need for vaccinatio n: “Co-infection exacerbates the replication of one or both of those viruses when they occur together, making the combination much worse than a single infection.
“In the MAGIC investigation, we found PRRS pig vaccination correlated with decreased PCV2 vir emia (the amount of PCV2 virus in the bloodstream),” continues Dr. Walter. “This suggests there is benefit in controlling the PRRS component in mixed infections, as we already know there is in single, or uncomplicated, PRRS infections.”
For best results, address both pathogens, he emphasizes. “This approach is supported by a study by Dr. Randy Jones in North Carolina, reported at the
Leman Conference last September. The herd he was working with had an average finishing mortality rate of 14%,” points out Dr. Walter. “They implemented PRRS vaccination, and the average mortality rate was reduced to a range of 6-8%. Once PCV2 vaccine became available and was administered, average finishing mortality rates were further reduced to less than 4%.”
To summarize Dr.
Walter’s key points:

• PRRS pig vaccination is very effective in controlling the disease in pigs, which is an underappreciated aspect of PRRS. Many people focus solely on the disease in the breeding herd. The disease in pigs actually costs much more, and there is a huge amount of opportunity by controlling the disease in this production phase.
• With PCVAD, PRRS is the most common co-infection.
• Co-infection increases the replication of one or both of the viruses, making the combination much worse than a single infection.
• There is benefit in controlling the PRRS component in mixed infections, as there is in single infections.
• For best results in cases of PRRS-complicated PCVAD, address both infections.