Porcine reproductive and respiratory syndrome (PRRS) is not like other viruses. Despite decades of research and advanced biosecurity measures, the battle still wages on. In recent weeks, the PRRS incidence has increased and is higher than in previous years, says Dr. Gustavo Silva, DVM and associate professor of vet diagnostic and production animal medicine at the Iowa State University College of Veterinary Medicine.
The current rise is primarily driven by growing herds while breeding herds remain relatively low, he told the crowd at the Annual Swine Conference in Quincy, Ill.
“New variants move fast – and reach good farms, too,” Silva says.
Gone are the days of thinking you are “safe” from PRRS. New variants popping up unexpectedly in previously healthy hog regions of the country are challenging the pork industry to think differently.
“The virus is changing so we need to change how we deal with it,” Silva says. “How can we better use tools available today to make this battle a little more fair?”
Why is PRRS Trickier Than Ever?
PRRS is harder to control than other viruses. Not only does it rapidly evolve and have a high strain diversity, it can also move through multiple transmission routes from direct contact and aerosols to fomites and movement. It persists in pigs and survives longer in the cold than other viruses, Silva says.
None of this is new information, so why is PRRS getting tougher to figure out? Silva notes three major challenges:
- Clinical signs vary from subclinical infection to severe reproductive and respiratory disease.
- Control is not one-size-fits-all. Different strains and systems require different responses.
- Farm connectivity amplifies spread. Pig flow, people, trailers and supplies can link sites.
Historically, the industry faced a highly destructive PRRS strain roughly every 10 years. Today, devastating new variants emerge every two to three years.
PRRS was once considered a winter-dominated disease. But farms today are experiencing severe summer outbreaks. Some modern strains can survive at room temperature or warmer temperatures (up to 97°F) for up to 24 hours, and up to seven days in cold winter environments.
Does Biosecurity Help?
Efforts to reduce introduction risk and reduce spread risk work, Silva notes. However, studies identify animal movements, close proximity to other swine sites, rendering services, shared employee housing, and manure pumping as the top risk factors for PRRS introduction today, Silva notes. Successful risk-reduction strategies include strict hygiene and disinfection, composting instead of rendering, dedicated manure pumping equipment and enforced operational downtime.
“We need to believe that they work and stay together,” Silva says. “Research proves they do, but we have to execute the biosecurity protocol correctly.”
For example, long-term data show that air filtration is a valuable biosecurity tool that reduces the risk of PRRS outbreaks on sow farms by 50% compared to non-filtered farms. Silva says it’s important to ensure rigorous, audited maintenance occurs because filtration only works if the filters are properly maintained over time.
Best Practices to Fight PRRS Outbreaks and Stabilize Your Herd
A program at Iowa State University, the PRRS Outbreak Management Program (POMP), tracks what people are doing in the face of a PRRS outbreak on a sow farm.
Data from POMP indicates that naive herds suffering a break should aim for total virus elimination. Herds targeting complete “negative” status are twice as likely to achieve stability compared to those trying to settle for low-prevalence co-existence.
To minimize time-to-stability (returning to consistently weaning PRRS-negative piglets), Silva says herd closure is the most effective protocol. Crucially, herds must be closed within two weeks of an outbreak; delaying closure yields virtually no benefit over doing nothing.
“Know what’s in your acclimation material,” he advises. “Unscreened Live Virus Inoculation (LVI) can carry multiple PRRS virus strains and other pathogens. Standardize it, screen it, or use Modified Live Virus (MLV).”
Some producers utilize half-doses of MLV for grow-finish pigs to save costs, but data reveals a 3.4 times higher mortality rate when half-dose vaccinated animals are hit by a wild PRRS strain, he points out.
Stop Operating Out of a Silo
Individual farm biosecurity is no longer enough because swine operations are highly interconnected. Through initiatives like the PRIME project, Silva says the industry is building secure, anonymous data-sharing networks.
“What we are creating is an ecosystem where we can see each other,” Silva says. “We can see the status of PRRS, and then by merging diagnostics and real-time movement information, we can see where those pigs are going to, where they came from, the current status, and then help communicate with farms.”
The idea behind PRIME is that communication is essential to understanding the health risks to your farm. This ecosystem allows neighbors to communicate, visualize incoming threats, and proactively manage dynamic risks before the virus reaches their gates.
“This model tries to forecast the risk of the disease in the horizon, so you guys can manage the disease in real time because risk is dynamic,” he says.
To combat this evolving threat, Silva urges the industry to move toward coordinated regional data-sharing and collaborative real-time risk forecasting. Now is not the time to take these increased PRRS outbreaks for granted.
