A highly virulent strain of Porcine Reproductive and Respiratory Syndrome virus (PRRSV) has renewed focus on the importance of disease surveillance and vaccination programs in the province.
Swine Health Ontario (SHO), along with the Ontario Pork Industry Council and Ontario Pork, recently held a webinar for producers and industry to highlight veterinary and producer experiences with PRRSV in the province and the Midwest U.S. Speakers underscored the need for a co-ordinated approach to surveillance of the disease among producers and industry in Ontario using Swine Health Ontario’s Area Regional Control and Elimination (ARC&E) program.
Why it matters: PRRSV represents the biggest economic loss for Ontario swine producers, so better surveillance and diagnostic data can help reduce losses.
Although there are hundreds of strains of PRRSV, Dr. Marty Misener of South West Ontario Veterinary Service (SWOVS) says his practice, which focuses solely on swine health, sees three predominant strains in the province: 1-1-1, 1-201-1 and 1-8-4. The 1-8-4 is a “very, very virulent strain” and the one causing the most significant loss.
Misener said PRRSV is perceived as a “giant elephant” (referring to the old adage that you can’t eat an elephant in one bite) and proposes that going forward “our industry should actually single out some very specific strains and throw a bunch of work at those strains. It’s a bite that we can, you know, bite off.”
That’s exactly what SWOVS research associate, Gillian Greaves, has been doing. Greaves discussed the clinic’s diagnostic insights from clients that have had PRRSV in the province, taking a “deeper dive” into data collected in the past five years.
The clinic looked at PRRSV diagnostics from January 2016 to April 2021 and noticed an increase in positive PRRSV cases within the last 16 months of the data set. Before November 2019, the average positivity rate of submissions to the Animal Health Laboratory (AHL) per month was 15 per cent, but it has since increased to 19 per cent, “which is significant,” she said.
Greaves said SWOVS has been working on streamlining its diagnostic database by using statistical programs that combine datasets from AHL, making it more automated and usable by pairing diagnostic and production data together. The benefit, she said, is it allows SWOVS to gain insights on strategies and production practices and relate them to how long it takes for farms to return to their baseline production.
They can also create heat maps to see when farms or barns in surrounding areas are going positive or negative, “and drill down into specific strains,” she said. The purpose of this type of surveillance is to better support pork producers, improve the functionality of SWOVS’s data, and have the industry focus on learning from collective experiences, she said.
Rethinking PRRSV vaccination
Although vaccination can help prevent PRRSV, “here in Ontario, we haven’t been super aggressive with utilizing PRRS vaccine,” Misener said. “But with continued pressure and more outbreaks and prevalence, I believe we need a re-think and be more aggressive in using that tool in the best way we possibly can.
“I suggest everybody scratch their head and think about where that’s applicable to your farm in very pig dense areas.”
He says that more growing pigs will be vaccinated, “and certainly anyone with sow herds in high-risk areas needs to consider a well-thought-out vaccination strategy.”
The biggest hurdle to eliminating PRRSV is significant knowledge gaps in how the virus is transmitted.
“There is no smoking gun,” said John Otten, swine production manager with Floradale Feed Mill. He presented a case study of a farm in Perth County that dealt with PRRSV last summer despite having a consistent sow herd with “leading-edge performance.”
He said in 18 years, the site has had four PRRSV infections, all with successful elimination. Long-term, reliable staff are present, and gilts are exposed early in life to a modified-live PRRS vaccine with a 90-day cool down period and produces PRRS-negative pigs with surveillance at the nursery.
In June 2020, some sows started going off feed and some died, “and by the third day, we knew we had some suspicion,” he said. The farm was confronted with an aggressive PRRSV strain (which they found out via testing was the 1-8-4 strain). That brought “high and fast mortality” in the farrowing rooms, as well as rapid sow and pregnancy losses. Some nursery groups experienced 20 per cent mortality, “and of course the finishing barns did not perform as well as we would have liked.”
Knowing it was an aggressive strain, “we knew it would be a haul to get the herd stabilized.”
The farm surveyed daily, monitoring lactation, ambient temperature, piglet deaths and stillborns and looked at weekly averages to know when the best use of serum inoculations would be.
The next step was to review possible sources of transmission. The farm reviewed biosecurity protocols with staff and suppliers. Otten said it could have resulted from a procedural drift, but no smoking gun could be found.
Three nearby sites were affiliated with the farm and tested negative. Otten credits the use of SHO’s ARC&E program for helping the farm reduce risk to other farms and farm sites, particularly those close to sows. ARC&E is a voluntary surveillance system that uses health data given by producers and GIS mapping to track disease.
Otten stressed that understanding what vectors of movement are common to pork producers is key to prevent spread and assessment of sites is needed when moving pigs.
Ontario is keeping a close eye on another highly virulent strain in the U.S. known as the 1-4-4 1 c variant.
Managing a new variant
Mark Schwartz, is manager of production systems for Schwartz Farms Inc., a family-owned pork producer that has approximately 6,000 sows and 14 sites in Minnesota, Nebraska, South Dakota, and Iowa. The company has been battling this variant since February and is causing morbidity and mortality that he’s never seen with other strains.
“It’s been a very frustrating and humbling experience.”
The company has been performing detailed surveillance on production and pig movement between sites, shared suppliers with other companies and other company sites. He hopes having a robust collection of data will provide some answers on how to prevent further transmission.
“We need to look at the density of pig production and the movement of animals,” he said.
“Surveillance is obviously critical to being able to control and eliminate disease,” said Jessica Fox, SHO interim general manager. She encourages Ontario pork producers to enrol in the ARC&E program, as it has undergone extensive revisions and recently launched a new website. Producers need to re-enrol, even if they were previously enrolled due to these changes.
Misener said the industry “needs to manage our expectations as we move forward with ARC&E.”
He noted there was an undercurrent of frustration among producers that the site status was not being kept up to date. But the tool works.
Misener said that although ARC&E wasn’t used to its full capabilities with Porcine Epidemic Diarrhea (PED), “we used it quite a bit and that really helped with our success in containing it and not having it go endemic.”
He said that unlike the big U.S. companies such as Schwartz Farms that can quickly collect more robust data, the Ontario industry must rely on reporting from individual producers. Doing so is “hugely important” and it will be much easier to manage PRRSV and other diseases, he said.
He said what he’s most excited about moving forward is that ARC&E can be used “as part of a containment strategy. As an industry, if we can work towards better containment of those really nasty strains, it’s going to benefit everyone.”