During a World Pork Expo news conference, the National Pork Board announced a new initiative aimed squarely at taming the unrelenting porcine reproductive and respiratory syndrome (PRRS) virus.

Dave Culbertson, a pork producer from Geneseo, IL, said the Pork Board's Swine Health Committee has long recognized the significance of PRRS to the U.S. pork industry, having allocated over $2 million in checkoff funds for research since 1990.

“In spite of nearly 15 years of dedicated effort toward developing tools and management strategies for managing this disease, U.S. producers still list PRRS as the number one, most economically significant disease in their operations,” Culbertson noted. “Preliminary data from ongoing studies suggests that PRRS is costing the U.S. swine industry $600 million per year.

“The Swine Health Committee has been working over the last several months to develop a comprehensive and coordinated national strategy that will result in the creation of predictable methods and tools for control, and possible elimination, of the PRRS virus from U.S. swine farms,” he added.

Solving the PRRS Puzzle

“We're starting to gain some knowledge and tools (for controlling this disease) as we move forward,” noted Beth Lautner, DVM and vice president of science and technology at the Pork Board. “But, at the same time, we can't institute those tools into herds and predictably know that we really have this disease under control.

“There was a sense that the pork checkoff really needed to bring people together in an effort to really solve the PRRS puzzle,” she declared.

Eric Neumann, DVM and the Pork Board's director of swine health and information, added: “After dealing clinically with this disease in the field for better than 15 years, we're still being frustrated by the same kinds of problems we had five, 10 or 15 years ago.”

He explained several reasons PRRS is so tough to control:

  • The PRRS virus is a positive-stranded RNA virus, highly prone to mutation. These persistent mutations create strains with unique antigenic profiles that can result in poor cross-protective immunity. This makes vaccine development particularly challenging. Adding to the complexity of the challenge, a herd may have more than one strain of the virus or a new strain may be inadvertently introduced.

  • The PRRS virus elicits a rather complicated and unique immune response. This has hindered vaccine development, management and elimination strategies.

  • Anecdotal evidence strongly suggests that the virus can move between farms despite rigorous biosecurity and production practices. Greater understanding about aerosol transmission and biological and physical vectors is needed.

  • Finally, having relatively few tools available to manage and control the disease compounds the problem.

Goals for the New Initiative

Following several months of collaboration with producers, veterinarians, universities, researchers, companies and state and federal government agencies, the Swine Health Committee developed a strategy matrix with 13 key objectives. At the conference, Neumann reviewed each briefly:

  1. Cooperative vaccine development: With limited vaccine options currently available, the committee emphasizes the need for more work and resources aimed at vaccine development. “If we use other diseases in the swine industry as a model, notably pseudorabies (PRV) and classical swine fever, the vaccines were an important part of managing and controlling those diseases,” Neumann noted.

  2. Understanding the persistently infected pig: “The PRRS virus is notable for its ability to develop long-term, persistent infections that complicate control and elimination programs,” he said. Those mechanisms must be understood so that testing strategies can be developed to identify persistently infected pigs.

  3. Creation of PRRS virus typing systems: With the virus' remarkable ability to mutate into new strains, a system for categorizing the new strains into similar “families” will facilitate vaccine development and regional PRRS elimination programs. “Because it mutates very readily, what infects a herd one day can mutate and infect the herd down the road, or reinfect the same herd simply because we lose the immunologic protection from the original virus,” he explained. “Epidemiologically, it looks like there is value in being able to classify these viruses into smaller groups so we can target vaccine development or regional vaccination programs.”

  4. Immune therapy development: Antiviral compounds and immune therapy have proven to be useful in controlling some other diseases; however, their application to PRRS has not been fully investigated. These products directly impact the virus rather than working through the immune system.

  5. National epidemiological investigations and risk factor analysis: “We've got herds that break with this disease, and despite our best efforts, we have a lot of difficulty in understanding where the infection came from. There's a strong, immediate need to understand the factors that put a farm at risk, across production types and geography, and on a large-scale basis,” Neumann explained.

  6. Creation of regional PRRS elimination demonstration projects: “We know we can eliminate this virus from a farm, but at this point, we don't know how to eliminate the virus from a region. We need to develop projects to learn how to do that,” he said.

  7. Quantifying the cost of PRRS to the U.S. pork industry: A thorough assessment of the cost of the disease will provide justification for the financial commitment necessary to complete the objectives outlined in the national PRRS initiative, Neumann stressed. “We really don't know what this disease is costing the industry as a whole,” he said, noting the $600 million is based on an early look at the data.

  8. PRRS virus genomic sequencing and creation of a national database: An enormous amount of diagnostic information about PRRS outbreaks and characteristics of the specific virus strains already exist. Unfortunately, the data has not been collected and stored in a manner that allows researchers to effectively analyze it. A national database would catalog old strains and new outbreaks for more effective analysis.

  9. Understanding the mechanisms of between-farm viral transmission: “We need to do more viral transmission research and understand what the mechanisms are so we can put mitigation strategies in place,” Neumann said.

  10. Engagement with the work of international PRRS researchers: “PRRS research is conducted around the world, and we need to make sure we have the due diligence to understand the application of the research on the U.S. pork industry,” he stressed.

  11. Collaboration with researchers of related (non-swine) viruses: Viruses that are related to PRRS exist in other species. It is important to track the global research to see if it might have application to the pig virus.

  12. Publication and distribution of 2003 PRRS compendiums: The first comprehensive review of scientific literature on PRRS, published in 1998, has been updated. The complete edition, primarily for use by veterinarians and researchers, is available for $30. An abridged version, providing practical information for pork producer use, is available for $10. A searchable CD containing both versions is available for $20. To order copies, call 800-456-PORK or visit www.porkboard.org.

  13. Development of a real-time PRRS information/education system: A real-time system for disseminating new information to producers and veterinarians will be developed.

Time and Money

A detailed plan of work will be developed to prioritize the list of objectives and focus on long-range (10-15 years) research programs, Neumann explained.

In addition to checkoff funds, financial support will be sought through the USDA Agricultural Research Service, Animal & Plant Health Inspection Service (APHIS) Veterinary Services and competitive grant programs.

Asked whether PRRS can be eradicated, Neumann stated: “Clearly, yes it can. We know producers and veterinarians have eliminated it from farms. The means and methods for expanding that through the industry is the question.”

Why is PRRS so tough to eradicate? “PRRS is simply a different virus than PRV,” Neumann continued. “PRV is a good example of a virus for which we had a very effective vaccine and which could be differentiated from natural infections. There is only a single strain of (PRV) virus, so there wasn't concern about variation between farms.” PRRS, unfortunately, doesn't fit that model. “We don't have a vaccine that is differentiable from live infections, and PRRS virus mutates readily,” he added.

“As we discover new information and find answers to these tough questions, our goal is to be able to develop tools for producers to either control the disease in a manageable, predictable way, or provide opportunities to eliminate it,” Lautner explained.