Study Tracks Transboundary Spread and Novel Lineage Emergence of PRRSV-2 in North America

The Swine Health Information Center supports forward-looking research that fulfills its mission to strengthen the industry’s ability to detect and respond to emerging disease threats. A recent study published in March 2026 in the journal Pathogens, led by principal investigator Dr. Kim VanderWaal at the University of Minnesota, directly addresses that mission by advancing knowledge of PRRSV-2 strains across countries in North America. Understanding routes for transboundary spread of endemic viruses such as PRRSV-2 helps inform emerging disease risks and mitigation strategies.   

The full study can be accessed in the journal Pathogens here. 

PRRSV-2 remains one of the most economically significant diseases affecting swine production globally, with substantial impacts on productivity, animal health, and international swine trade. This study provides one of the most comprehensive analyses to date of PRRSV-2 genetic diversity in Canada, while also offering critical insights into transboundary dynamics between Canada and the US. By analyzing more than 3,000 viral sequences collected over a 24-year period in five Canadian provinces, this research delivers a clearer picture of how the virus evolves, spreads, and persists across borders. 

A key contribution of the study is its demonstration of how disease data availability can expand the understanding of disease dynamics. Historically, there were fewer publicly available PRRSV-2 sequences available from Canada for comprehensive analysis. The previous use of the lineage and sub-lineage classification was based on lineages established using sequences from before 2008, which differs from the current classification system accounting for more recent viral diversity. By significantly expanding the dataset, this research helps close that gap and provides a stronger foundation for future work. It also highlights the ongoing need for enhanced genomic surveillance, particularly in underrepresented regions. 

The identification of previously unrecognized genetic diversity within PRRSV-2 populations in Canada is a central finding of the analysis. While 13 known sub-lineages were detected, approximately one-third of the sequences could not be assigned to any known sub-lineage. Through detailed phylogenetic analysis using global reference sequences, these unclassified viruses were grouped into four distinct clades. The four clades had genetic distances >9.5% from the recognized sub-lineages, leading to the identification of two novel lineage designations (sub-lineages 1K and 1L) while the other two clades were rare and last detected in 2021. These newly defined groups are highly divergent from previously known sub-lineages and have circulated in Canadian swine populations for decades, highlighting how much viral diversity remains to be fully characterized. 

The discovery of these novel lineage groups is more than a taxonomic update. It provides practical advancements for surveillance and disease management. Accurate classification enables veterinarians, producers, and researchers to better track virus movement, understand epidemiological connections, and implement more targeted control strategies. The study also expands the variant classification system used in the US, aligning Canadian data with existing frameworks to improve communication and coordination across borders. 

The forensic analysis reconstructing cross-border transmission histories reveals that several sub-lineages—including 1C, 1H, 1I, 1K, and 1L—originated in Canada, and sub-lineages such as 1A, 1B,  and 1E were found to originate in the US and later enter Canada. These findings underscore the bi-directional nature of PRRSV-2 movement, although many transmission patterns were predominantly one-directional depending on lineage. Canada and the US maintain one of the most integrated swine trade relationships in the world, with millions of live pigs moving between the two countries annually. This movement can create opportunities for transboundary PRRSV-2 dynamics.   

The data provides evidence for existing variation in transmission of different sub-lineages across borders. Some lineages had limited exchange, suggesting geographic structuring and possible containment through biosecurity measures, while others demonstrated more frequent transboundary movement, including repeated introductions and re-introductions between countries. Notably, sub-lineage 1K appears to have emerged in Canada and more recently spread into the US, though it has not yet become widely established. The detection of this recent introduction was only possible due to the new genetic classification system adopted by veterinary diagnostic labs in the US.   

These findings offer important insights for guiding targeted surveillance and biosecurity strategies aimed at preventing the cross-border introduction of PRRSV-2 variants not yet detected in either country. By identifying where lineages originate and how they move, stakeholders can better focus monitoring and prevention strategies, particularly at national borders and in high-traffic trade corridors. Improvements in biosecurity protocols and practices, especially those implemented after the early 2000s, may be influencing more recent patterns of viral spread, as much of the inferred transmission between countries happened before the most recent decade. 

From a broader perspective, the study illustrates the value of SHIC-funded research in advancing innovation. By supporting large-scale genomic analysis and the development of new classification tools, SHIC enables the industry to stay ahead of evolving disease threats. The ability to detect emerging, novel lineage groups and understand their transboundary movement is essential for protecting herd health and maintaining the resilience of the North American swine industry. 

Ultimately, this research reinforces a key disease management principle: pathogen transmission does not stop at national borders. PRRSV-2 is a dynamic, evolving pathogen shaped by animal movement, trade, and local conditions. Continued collaboration, data sharing, and investment in research will be critical to staying ahead of its impact and translating lessons learned to the next emerging disease. 

Reference:  

Herrera da Silva JP, Paploski IAD, Charette R, Dufresne L, Messier S, Bolduc J, Kikuti M, Pamornchainavakul N, Corzo CA, VanderWaal K. Phylogenetic Lineages of PRRSV-2 from Canada Reveal Patterns of Transboundary Spread and Two Novel Sub-Lineages in North America. Pathogens. 2026; 15(4):346. https://doi.org/10.3390/pathogens15040346

The Swine Health Information Center, launched in 2015 with Pork Checkoff funding, protects and enhances the health of the US swine herd by minimizing the impact of emerging disease threats through preparedness, coordinated communications, global disease monitoring, analysis of swine health data, and targeted research investments. As a conduit of information and research, SHIC encourages sharing of its publications and research. Forward, reprint, and quote SHIC material freely. For more information, visit http://www.swinehealth.org or contact Dr. Megan Niederwerder at [email protected] or Dr. Lisa Becton at [email protected].