A gene-edited pig that resists Porcine Reproductive and Respiratory Syndrome now sits firmly on the radar as a possible new tool to control one of the most costly and persistent diseases facing the global pork industry.
Porcine Reproductive and Respiratory Syndrome, commonly known as PRRS, first appeared in the late 1980s and quickly earned names such as “mystery disease” in the United States and “blue ear disease” in parts of Europe. Since then, the virus spread worldwide and continues to challenge producers, veterinarians, and researchers. The disease affects pigs of all ages, but it hits sow herds and young piglets hardest. In grow-finish barns, PRRS often weakened the immune system, opening the door to secondary infections that compounded losses.
Dr. John Harding, a professor in the Department of Large Animal Clinical Sciences at the Western College of Veterinary Medicine, said bio-security continued to stand as the first and most important line of defence against PRRS and many other swine diseases. He said every control strategy still started with preventing the virus from entering a barn.
“In terms of PRRS, we’ve looked at the various options that are available for control,” Harding said. “The one big one on the radar now, particularly in the U.S. and hopefully soon in Canada, is the PRRS-resistant pig.”
Researchers developed the PRRS-resistant pig using gene-editing technology. Harding explained that the virus relies on a specific receptor to enter pig cells and replicate. Scientists altered that receptor so the virus could no longer bind to it.
“The advantage of this pig is that it will not get infected with PRRS,” he said. “The main point is it is not susceptible.”
Harding stressed that the science behind the technology showed strong promise. At the same time, he acknowledged that adoption raised broader questions beyond animal health. “Whether we want to support the technology or not is a decision we all need to make individually,” he said. “In my opinion, the science is good. Public perception and market risk are concerns we need to think about.”
PRRS continued to evolve since its discovery. Harding said the virus belonged to a family of RNA viruses, which changed frequently through mutation and recombination. Over time, new strains emerged while others faded away. He noted that producers often feared new strains as more severe, but research did not always support that assumption.

“New strains are not necessarily worse,” he said. “Sometimes they are less virulent. Sometimes they are more virulent.”
Transmission remained one of the virus’s greatest challenges. PRRS spreads through direct pig-to-pig contact, contaminated equipment, feed, water, and transport vehicles. Harding said aerosol spread likely played the biggest role at a regional level, especially in areas with high hog density.
He pointed to renewed research that reinforced the value of basic bio-security practices. Parking locations, manure handling, downtime between farm visits, bench entry systems, wildlife control around feed bins, and properly cleaned transport trucks all played meaningful roles in reducing risk.
Harding said hog density largely explained differences in PRRS pressure between regions. Western Canada, with lower hog density, experienced fewer and less severe outbreaks than parts of the U.S. Midwest. In Eastern Canada, regions with dense hog populations faced higher ongoing risk.
Diagnostic tools also improved significantly over time. Harding said antibody tests helped confirm exposure in chronically infected herds or verify negative status in clean herds. PCR testing, which detected viral genetic material, advanced rapidly and allowed veterinarians to identify active infections with greater sensitivity and precision.
Sample options expanded as well. In addition to blood and tissue samples, producers now use oral fluids, processing fluids, and tonsil-based sampling to answer specific diagnostic questions. Harding said test selection always depended on the herd’s health status and the producer’s management goals.
Despite technological advances, Harding returned repeatedly to fundamentals. He said producers needed to understand their neighbours’ health status, manage animal sourcing carefully, use quarantine barns properly, and maintain strict personnel entry protocols.
“Bio-security works,” he said. “It’s an expense, but it pays dividends.”
Harding said PRRS would not disappear. For negative farms, he urged vigilance. For positive but stable farms, he said producers might choose to live with the virus. In high-risk regions, elimination sometimes led to reinfection within a few years unless bio-security remained exceptionally strong.
Vaccination continued to play a role, but Harding cautioned that no vaccine provided complete protection. He encouraged producers to work closely with their veterinarians before making major control or elimination decisions.
As interest in the PRRS-resistant pig grew, Harding encouraged producers to seek credible information and professional guidance. He pointed producers to their veterinarians, current swine disease references, and independent research sources to fully understand both the science and the implications.
“PRRS costs the industry a lot of money,” he said. “It’s a disease we need to take seriously.”
For more information on the PRRS-resistant pig, Harding directed those interested to prrsresistantpig.com •
— By Harry Siemens