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What are the emerging PRRS virus strains in U.S. and beyond?

Of the 34 million pigs in Spain, 18 million have been impacted by Rosalia.

March 30, 2023

4 Min Read
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As porcine reproductive and respiratory syndrome virus strains continue to affect pork production in the United States and around the world, the Swine Health Information Center and the American Association of Swine Veterinarians recently held a webinar to provide the latest information on challenges caused by emerging strains of this virus. Presenters addressed the PRRSV L1C variant of RFLP 1-4-4 and PRRSV L1C 1-2-4 affecting the U.S. swine population, and Rosalia, a PRRSV-1 strain with increased virulence affecting swine production in Spain.  

Rosalia impact
Eric Mateu, Autonomous University of Barcelona (Spain) told attendees 18 million pigs in Spain have been impacted by Rosalia. For perspective, there are 34 million pigs total in Spain and 146 million in the EU. The primary area impacted spans 31,000 square miles in the northeast quadrant of the country. In the area of greatest prevalence, 1,000 sow farms, averaging 1,400 sows each, are present. Further, 490 farms with nursery operations exist in that area of viral circulation and 8,000 farms where pigs are finished. On sow farms, the PRRS vaccination rate is 70%, less than 20% of nursery farms are vaccinated, and less than 5% of finishing farms.

Spanish pork producers affected by Rosalia experienced abortion storms in sow herds, sow mortality, stillbirths, high mortality in suckling piglets and weaners, fewer health issues in finishing pigs, but decreased feed conversion rates. Mateu said these realities resulted in a high economic impact. On average, the most affected farms lost 15% to 20% of their annual income.

His presentation also included statistics on Rosalia consequences as it has affected production in waves. Mateu said Spain is probably in a phase with decreasing impacts though the industry remains vigilant in its efforts to combat Rosalia's impact. Vaccination, McRebel (management changes to reduce exposure to bacteria to eliminate losses from PRRS), changing farrowing schedules, and depopulation have all been implemented with varying results.

Diagnostic data
Daniel Linhares and Giovani Trevisan, Iowa State University, shared information about PRRSV monitoring on the Swine Disease Reporting System, a SHIC-funded collaborative project among five veterinary diagnostic laboratories. SDRS shares information on the activity of endemic and emerging pathogens affecting the U.S. swine population, assisting veterinarians and producers in making informed decisions on disease prevention, detection, and management.

Using data collected from the five veterinary diagnostic labs participating in SDRS, Linhares and Trevisan shared information on PRRSV evolution and genetic variability across states. Data included information on PRRSV L1C RFLP 1-2-4. From 2009 to 2021, per SDRS, there were 421 detections of this strain; then in 2022, there were 264 classifications. Their data shows PRRSV L1C variant is still an eminent animal health and production threat and is moving east, threatening 1.5 million or more sows in 2023. They reminded webinar participants of the importance of biocontainment and biosecurity in eastern states to prevent introduction of that strain into pig populations at risk in that region.

On-farm experience
Minnesota-based practitioner Paul Yeske shared information on what to consider during a PRRS outbreak and herd closure, also addressing depopulation/repopulation strategies. When moving through the early days of a PRRS break, Yeske said abortions and farrowing sows with retained pigs are the most common cause of sow mortality. Assisting sows in this process, just as assisting with farrowing, is essential.

His advice also included increasing breeding targets as much as possible, breeding back sows that aborted, and identifying open sows as soon as possible. To save pigs, Yeske recommended moving piglets as needed and treating them more aggressively.

Regarding herd stabilization, Yeske walked through three scenarios: allow herd to remain positive, eliminate the field strain and depopulation/repopulation. He shared processes, recommendations and results as well as timelines. The overview addressed McRebel-like procedures and Yeske's cautions regarding its implementation, diagnostic monitoring and an early weaning strategy. Depopulation/repopulation as a tool to address PRRS breaks serves as a viable strategy in the U.S. production model due to multi-site production.

When talking about biosecurity, Yeske emphasized the need for bio-containment, or how to keep the virus on the site, as equally essential to bio-exclusion, keeping the virus out. He said bio-containment is the forgotten part of biosecurity, a process addressing showering out of barns and handling mortalities as well as disposal of boots and coveralls among other practices.

Clayton Johnson, Carthage Veterinary Services, shared experience with PRRSV breaks on three sow farms, each varying in intensity along with remarks on what's working to combat PRRS. Biosecurity, understanding PRRSV strain lineage and PRRS vaccination all have been effective tools for PRRS management. However, herd closure, prevention of latent PRRS clinical resurgence, regional PRRS management programs and grow/finish biosecurity are all opportunities that need attention. Johnson said questions surrounding the origin of PRRSV strains lead to confusion as does knowing where the emerging strain will display virulence, and how isolate specific PRRS management strategies should be.

A discussion on tools needed for PRRSV break management was part of Johnson's presentation as well as identification of research needs. He suggested the industry may need a working group with a focus on the latest novel PRRS strain. Another research need is barn-level examination on piglet vaccination, piglet antibiotic administration at weaning, pre-farrow vaccination of sows and the impact of McRebel.

Complete presentations, as well as attendee questions for speakers, are all included in the full webinar available on the SHIC website.

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