Swine genomic markers, phenotypes, chromosomes and genotyping are playing an increasingly important role in the latest efforts against porcine reproductive and respiratory syndrome (PRRS) virus. The science of genetics will play a vital role in the development of PRRS-resistant pigs and eventual elimination of the disease, according to Dr. Bob Rowland, professor of Diagnostic Medicine and Pathobiology, Kansas State University.
Rowland is executive director of the PRRS Coordinated Agricultural Project (CAP). The objective of the USDA-funded research program is to develop a roadmap for the eventual elimination of the PRRS virus.
The control and elimination of PRRS is likely the most challenging task facing the swine industry worldwide. Several factors related to the biology of the virus make disease detection and elimination extremely difficult.
In addition, PRRS control efforts are hampered by a lack of effective means to protect naïve herds from infection. Recent efforts have focused on regional initiatives intended to eliminate the costly disease from one specific geographic area at a time. One example of success is the Stevens County project in Minnesota, which has attained a PRRSV-negative status and has been expanded to include all of northern Minnesota.
“The PRRS virus is the most rapidly changing virus on the planet, plus it is stealthy, persistent and easily transmitted,” Rowland says. “The virus circulates very nicely within a production system. It might go away for a time but it keeps coming back.”
Regional control initiatives, air filtration of barns, and vaccine technology are important steps but there is no magic bullet in the battle against PRRS, Rowland says. “We need to bring all those things to bear if we are to win the battle against the disease.”
Rowland looks at PRRS not as an individual pig disease but as a population disease—one that causes economic loss by reducing herd performance. “All the infectious diseases in the history of swine production combined have had less economic impact than PRRS has had over the last 15 to 20 years,” he says.
The National Animal Health Monitoring System estimates that 21 percent of U.S. swine farms have the disease. Rowland believes up to 60 percent of farms have the virus.
Current research being conducted with the PRRS CAP centers around improvement in swine genetics, or improving the pig’s tolerance to the disease, according to Rowland. “Some pigs don’t care if they have the virus and maybe these are the type of pigs we should be breeding.”
Rowland says that it could be possible to breed pigs that are “vaccine-ready” and that would respond better to vaccine. “Maybe we should think in terms of bringing the pig to the vaccine, rather than the vaccine to the pig” he says. “We will see more work in the area of genetic modifications that will bring more favorable genes into a pig. We can breed pigs that are PRRS resistant.”
“The PRRS Host Genetics Consortium (PHGC) is the first-of-its-kind approach to disease research and is playing a vital role in understanding how swine genetics can influence the outcome of PRRSV infection,” Rowland says. “Results also have identified new avenues for other areas of PRRS research, including new diagnostic techniques, new surveillance approaches and a better understanding of virus ecology.”
“It is a visionary approach to the industry’s efforts against PRRS,” according to Rowland. The effort involves integration of state-of-the-art genomics research and the latest advancements in virology. “It is a unique approach and involves PRRS researchers, swine genome scientists, National Pork Board (NPB) animal health specialists and breeding companies.”
The Consortium establishes a multi-disciplinary, multi-national team of researchers to advance these efforts, and 13 trials involving 2,600 pigs have been completed, according to Rowland. “We are identifying genes that infer PRRS resistance.”
USDA and NPB are key funding sources for the Consortium. Total funding for the effort has reached $15 million to $20 million, Rowland says. “There is no single company or entity with the resources to conduct this project.”
The database created thus far by the Consortium will provide future researchers with crucial results to conduct ongoing PRRS research.