Swine veterinarians wrestling with two diseases -
Every swine veterinarian fears two acronyms—PCVAD and PRRS.
The acronyms refer to porcine circovirus-associated disease, which practitioners often see as postweaning multisystemic wasting syndrome, and porcine reproductive and respiratory syndrome.
The American Association of Swine Veterinarians is turning more attention to PCVAD as the disease emerges in North America, while the association is still moving forward with the goal of eliminating PRRS from the continent.
Both PCVAD and PRRS were major subjects at the AASV annual meeting.
Dr. John Harding of the University of Saskatchewan Western College of Veterinary Medicine gave an overview of "Porcine circovirus diseases: The brutal facts."
Dr. Harding said PCVD, PMWS, and PCVAD are essentially all the same. Porcine circovirus type 2 is a primary pathogen that can lead to severe disease in combination with co-factors.
Yet, veterinarians wonder why a virus that has been prevalent for years has suddenly started to lead to such severe disease. Dr. Harding said PCV2 appears to affect the immune system at a deep level and in a very subtle way.
Dr. Harding's "brutal facts" included the following:
- Changing the name from PMWS to PCVAD in North America has caused some confusion. European researchers studying porcine circovirus diseases prefer the term PCVD, rather than PCVAD.
- PRRS is king in North America, which lags in PCV2 research and expertise.
- The role of co-factors is far from clear.
- Single pathogens do not exist in real life.
- Current production systems promote pathogen evolution to higher virulence. The concentration of animals increases the transmission of viruses that would once have died along with the hosts.
- Swine veterinarians need to round out their medical background to solve complex disease situations.
"The pathogenesis of porcine circovirus 2 infections" was the topic for Dr. Hans Nauwynck from the Faculty of Veterinary Medicine at Ghent University in Belgium.
Dr. Nauwynck said PCV2 is extremely resistant to inactivation and extremely slow to replicate, with a replication cycle of 36 hours. Isolates from different regions show a high similarity.
Dr. Nauwynck presented results from his group's research on PCV2 infections. Inoculation of embryos with PCV2 led to reproductive failure. Fetuses that received an inoculation at 57 or 75 days died before birth, but fetuses that received an inoculation at 92 days had no pathologic lesions at birth.
Dr. Nauwynck said most studies have not been able to induce PMWS in pigs with inoculations of PCV2 alone.
"Immunology of PCV2 infections" was the topic for Kenneth C. McCullough, PhD, of the Institute of Virology and Immunoprophylaxis in Switzerland.
Dr. McCullough said his talk could have included the subtitle "Or how to fool the immune system."
Dr. McCullough said viruses are "tricky little creatures" because they can activate or impair the immune system. In the case of PCV2, the immune system responds slowly to a persistent infection. If PCV2 reaches a certain threshold, Dr. McCullough said, it can inhibit the immune system's ability to recognize danger.
"It's a race against time for the immune system defeating this virus," he said.
Swine veterinarians also are racing against time to treat herds that develop a high-mortality syndrome in association with porcine circovirus. Dr. Tom Burkgren, AASV executive director, said only three vaccines have received approval in the United States—and none of them is readily available.
Some veterinarians have turned to a stopgap measure in an attempt to stem death losses of 20 percent to 30 percent. They take tissue from the lung, liver, or spleen of pigs with the infection. Then they kill the virus, dilute the sample, and inject the resulting homogenate into healthy animals to stimulate the immune system.
Veterinarians should be aware of possible pitfalls with this approach to treatment, Dr. Burkgren said. While federal regulations allow veterinarians to make vaccines within a veterinarian-client-patient relationship, they cannot take the products to other farms. The Department of Agriculture's Center for Veterinary Biologics has expressed concerns that formaldehyde might not wholly inactivate porcine circovirus. Finally, no scientific studies have assessed the efficacy of the approach—and anecdotal reports indicate varying responses.
Information is available in "The Issues Surrounding PCVAD Tissue Homogenate: What are the facts?" at www.aasp.org/news/story.php?id=2281.
On the research front, groups have begun giving grants for projects on PCVAD. The National Pork Board has committed $500,000 to research funding, with $300,000 from the Pork Checkoff and $200,000 from the Department of Agriculture. Last year, Boehringer Ingelheim Vetmedica awarded $75,000 in funding for the first time.
Even as porcine circovirus starts to take a toll in North America, the PRRS virus is still a major problem.
Dr. Paul Yeske of the Swine Vet Center in Minnesota gave an update on the North American PRRS Eradication Task Force.
Dr. Yeske said producers have expressed concern about hearing the words "PRRS" and "eradication" in the same sentence. He said eradication is the way to go, though, because PRRS is so costly.
Eradication will be a long-term process, Dr. Yeske said. "It's going to take a lot of local cooperation."
Dr. Yeske said the task force has established four immediate objectives with a number of action steps.
The first objective is to determine the roadblocks to eradication—such as producer misperceptions, lack of knowledge, or lack of confidence. The action step is developing questionnaires for producers and AASV members.
The second objective is to detail methods from other disease eradication efforts. The action step is gathering the information into a useable form.
The third objective is to develop industry-wide biosecurity practices. Action steps are producing a list of essential biosecurity practices for herd owners and managers, adding information about biosecurity to training manuals to build employee awareness, and producing a list of biosecurity inspection points for post-outbreak investigations.
The fourth objective is to develop guidelines for transporting pigs. The action step is creating a document as an aid to personnel education, biosecurity system management, and design of facilities and trailers.
Dr. Dale Polson of Boehringer Ingelheim Vetmedica spoke on the subject of PRRS risk assessment.
Particularly, Dr. Polson described the PRRS risk assessment tool that his company developed. He said the tool started out as a spreadsheet in 2002 to measure and manage PRRS risks on sow farms. By the end of 2004, the database encompassed 320 herd and site risk assessments.
In 2006, the company transferred the tool to the AASV, which has been training members how to use the software. Now more than 410 farms are in the database.
Dr. Polson said the data have shown an association between the risks that the software measures and actual outbreaks of PRRS. The risk assessment tool could serve as a benchmarking tool, he said, and also could help with the goal of elimination.
Dr. Michelle Jens of AMVC Management Services described how to use the tool on farms. The information categories include site characteristics, production data, herd health history, source herd records, replacement animal protocols, herd management, employee information, transportation biosecurity, and geographic information. Dr. Jens emphasized the need to talk to the employees because a farm's protocols might not be the actual practice.
Also during the AASV meeting, Boehringer Ingelheim Vetmedica announced the recipients of its 2007 Advancement in PRRS Research Awards. The company has awarded $25,000 apiece to three PRRS studies for the past five years.
Dr. Jeff Zimmerman of Iowa State University received a grant to develop an inexpensive and convenient method for PRRS virus monitoring, to evaluate the stability of PRRS virus, and to develop guidelines for handling and diagnostic monitoring of oral fluid samples.
Dr. Derald Holtkamp of Iowa State University received a grant to conduct a cross-sectional study of PRRS-positive breeding herds to evaluate the association between risk factors and a case definition on the basis of the number and severity of clinical episodes.
Dr. Robert Morrison of the University of Minnesota received a grant for work to estimate, quantify, and compare PRRS virus transmission information between pigs of various PRRS vaccination status.
The National Pork Board and the Department of Agriculture also give grants for PRRS research. In 2006, the National Pork Board backed 18 research projects with a total of about $1.5 million in Pork Checkoff funding. The USDA supports research through the PRRS Coordinated Agricultural Project.