Cover Story: OSHAB database one step towards a comprehensive PRRS elimination strategy

Thursday, June 10, 2010

Veterinarians are finding the PRRS database a valuable tool in tracking new strains of the disease and they hope that it will encourage the industry to move toward the next step, which is elimination

by KATE PROCTER

Porcine Reproductive and Respiratory Syndrome (PRRS) increasingly challenges the pork industry by its ability to mutate and move silently through the countryside.

"PRRS is changing," says Brent Robinson, who operates Vista Villa Genetics with his family near Walton. Having been PRRS negative for over two years, Robinson started thinking about protecting that health status with a "PRRS-free zone" in an area where they had control over several barns. "This would continue to protect ourselves and our customers," he says. He was hoping to talk to the few neighbours who had pigs close by and see if they could work together to keep the virus out.

Unfortunately, his good idea was thwarted when the virus came into one of his barns from one of several neighbouring barns which were PRRS positive. "That has made me a little less optimistic, but maybe a bit more realistic," he says. 

Robinson thinks that the way PRRS moves is changing. "Today, there is a lot more risk from aerosol transmission," he says. Keeping the disease out is a huge challenge in a pig-dense area. Producers can do everything right and it can all be for nothing if the virus blows in on the wind. Not only does PRRS seem more potent, the other diseases that emerge during a PRRS break can create a firestorm in the barn.

"It does appear that the new strains of the virus are more virulent," says Dr. Scott Dee, a professor at the Swine Disease Eradication Center, University of Minnesota Center of Veterinary Medicine. "As new isolates emerge, they can be highly virulent, cause significant disease, and cost producers more, both in losses and in animal suffering." He has conducted a study, accepted for publication in Veterinary Microbiology, that has shown that the PRRS virus can travel as far as 9.1 kilometres and still be infectious.

Dee, who has made the study of PRRS a central part of his work, says there are some data that support the hypothesis that pigs infected with very virulent strains have a higher amount of virus in blood and tissue than those infected with less virulent strains.

They also shed the virus more frequently in aerosols. However, more virulent strains cause more lesions, and other more serious clinical signs – quantity doesn't really matter.

Dee agrees that this makes it more important to eliminate the disease on a large scale rather than try to live with it. The National Pork Producers Council (NPPC) has recently passed a resolution, originating in Minnesota, to eliminate the virus from the United States voluntarily. While those involved in the Minnesota pork industry recognize the need for PRRS elimination, they are still working to develop a state-wide database that would allow practitioners to see the location and PRRS status of all pig farms in the state.

The Ontario Swine Health Advisory Board (OSHAB) has been working with the Animal Health Laboratory (AHL) at the University of Guelph for several years to develop a database that allows veterinarians to track how PRRS virus strains are mutating and moving through Ontario. After months of collecting information, the database is starting to prove its worth by enabling swine veterinarians to locate specific strains. They can also get details about how various strains affect herds, which enables them to give  their clients better advice on management strategies.

Virulent new strain
The database was put to the test in late 2009 when producers in southwestern Ontario were warned by veterinarians and OSHAB about a virulent strain relatively new to the area. Dr. George Charbonneau was one of the first to see this strain, with Restriction Fragment Length Polymorphism (RFLP) pattern 1-22-2, in a Middlesex County herd. The affected producer was selling feeder pigs. While he wanted the disease out of his herd, he was also very concerned about not spreading it to other producers, says Charbonneau.

This particular strain affected reproductive performance and piglet mortality, both before and after weaning. This herd saw post-wean mortality rates of 35 to 40 per cent during the worst of the outbreak, as well as sows aborting and farrowing early. "This virus had a better ability to get across the placenta and affect piglets in utero than other strains," says Charbonneau. It took about four months to get normal-quality piglets weaned out of the herd after the outbreak was diagnosed, he adds.

Since June 2007, 13 cases have been reported in southwestern Ontario, and the strain has also been identified in at least one lab in the United States. Ten of these Ontario cases have been reported since October 2009 and were concentrated in Lambton and Middlesex counties.

Charbonneau was able to get data on the first herd into the system and it didn't take long to see numbers that revealed something was happening with that strain. The strain was not entirely new to Ontario, having been seen in one Elgin County herd. But the database allowed veterinarians to see that there was a connection between the Elgin county herd and herds in Lambton and Middlesex counties. "We can basically compare notes across a much larger area. The database gives us an indication of a strain spreading in an area. It helps us understand how the virus is moving from farm to farm," explains Charbonneau.

The database gives vets the ability to do some of the epidemiology that confirms aerosol transmission is occurring, he adds, and shows that biosecurity strategies they are encouraging do work. For example, in the latest case, veterinarians were able to see that two infected farms were sharing a truck for moving pigs to market. "The OSHAB Database strengthens those observations by allowing us to go out further and see what is happening."

Dr. Glen Armstrong has used the database in his practice near Mitchell. When he looks at the database, it matches the strains but does not provide the location of the other strains. The consulting veterinarian is linked to the matching strains, which gives contact information and also the opportunity to discuss how that particular strain acts within a herd and which strategies are most effective.

"The biggest thing for me has been the ability to contact other vets and find out how they deal with it, as opposed to doing the same experiment over and over again," says Armstrong.

He was also able to use the database when the emerging strain started hitting southwestern  Ontario in the fall of 2009. The veterinary community tracked the progression of the virus earlier and came up with better strategies to manage it than they would have without it.

Armstrong reports that this particular strain has had a disastrous impact on the herds it has hit. He has seen significantly higher numbers of early farrowings, as well as high pre-wean mortality. There's been almost a complete loss of production for five or six weeks after the virus was first detected in a herd, with pre-wean mortality rates of up to 50 per cent and then an additional 50 per cent mortality rate in the nursery. "There's not a lot left," he says.

Armstrong is hopeful that using the database will also lead to a consistently applied PRRS strategy, with a significant number of producers and veterinarians on the same wavelength. In addition, the database has encouraged more openness within the industry, Armstrong adds. "It has encouraged conversation," he says. This conversation is helping the industry move toward the next step, which is elimination.

Armstrong is a strong proponent for a regional PRRS elimination strategy for the pork industry. "We really need to push for regional eradication," he says. Pig movement is one of the biggest challenges. "The industry is set up to move pigs."

Dr. Doug MacDougald a vet from Stratford agrees. "We just don't have any control over containment," he says. "We have a lot of questions with bad answers," he adds. Cull sows and the secondary pig market both result in animals moving around the countryside and there is currently no way of containing, monitoring or controlling this.

Charbonneau points out that right now, there is no organized effort to contain disease by location. "We should be working really hard to keep infected pigs out of certain regions," he says.

There are situations today where producers agree not to move PRRS-positive finishing pigs into a barn located next to a sow barn. "It is a mutually beneficial arrangement," says Charbonneau.

Proactive producers
While there are currently no government programs in place to monitor or control pig movement in Minnesota, producers have been proactive about voluntarily co-operating with each other to try to reduce viral spread. For example, producers who know they are PRRS-positive will communicate with their neighbours regarding the timing and location of pig movements. They may also do things such as vaccinate in order to reduce the amount of circulating virus.

A seven-county region of west-central Minnesota has succeeded in getting all but one producer within the zone PRRS-negative. Dr. Bob Morrison spearheaded this project. "Really, the producers end up doing it themselves. The farmers work together and work it out," says Dee.

It took about four years of regular meetings, obtaining funding, and convincing enough people that it was the right thing to do. They produced a map of the area, with red dots indicating PRRS positive and green indicating PRRS negative. As leading producers took charge and helped each other out, the map started to look greener. "The visual effect of the map was very powerful," says Dee. As more people worked at becoming PRRS-negative, others were encouraged to do the same, in part because there was less risk of re-infection if the neighbours were also negative.

As Ontario looks south, the industry has recognized the need to keep up and OSHAB has recently launched a regional PRRS elimination pilot project for a region in southern Ontario. Dr. Jane Carpenter has taken the lead role of Swine Disease Control Project co-ordinator.  The project is also supported by the Ontario Ministry of Agriculture, Food and Rural Affairs, Ontario Pork, and Animal Health Strategic Investment.

The selected region will have a moderate pig density, contain primarily sow sites, and have well-defined natural borders. Strong producer commitment is also one of the keys to success. OSHAB has already secured co-operation and help from Dee and Dr. Bob Morrison, key veterinarians in the Minnesota elimination project. Part of any elimination process includes filtration because "we're big believers that airborne spread happens in swine-dense regions," says Dee.

Minnesota sow farms are starting to retrofit barns with filtration systems. Great progress has been made in assembling teams of experts to get good installations, including sealing barns properly and ensuring proper ventilation to maintain excellent pig health. Team members include veterinarians, producers, engineers, academia, and installation experts.

Dee is currently conducting a study to determine filter sustainability over time. Preliminary results are encouraging, but Dee says that people need to change their mindset about filtration. They have learned a lot about retrofitting barns and have a better understanding of how to do it the right way, says Dee.

The Robinsons have considered filtration, but have not found a lot of expertise in Ontario. "People would be more willing to look at it if there was a local supplier who could come out and give good advice," he says. From a genetics company's perspective, filtration is worth it if the right technology is found. Robinson hopes that filtration technology will evolve to the point in Ontario where a demonstration barn or two will be available for producers to see.

Can PRRS be eliminated from a region? "It can be done if leaders help drive it forward from the producer side and people work together," stresses Dee.

Filtration and a good PRRS database are tools that will help the Ontario pork industry eliminate the virus for good. But, warns Robinson, success will not come easily. "You'll make some progress, and then there will be setbacks."

In spite of the challenges, Robinson thinks that a co-ordinated effort, including producers, veterinarians, input suppliers, and transportation companies, could be successful at keeping PRRS out. "Once you discuss the benefits of PRRS-negative status, it isn't a hard sell," he says.  However, a lot of producers will need some concrete evidence to show that it can be done. "More and more people will go from being naysayers to believers," he adds. BP