New World Screwworm: Fact Sheet & SHIC Article 6/10/2026 & USDA NWS Website
Pseudorabies Resources: Latest PRV Fact Sheet (Updated June 2024) & Additional PRV Resources/Links & Statement
New World Screwworm: Fact Sheet & SHIC Article 6/10/2026 & USDA NWS Website
Pseudorabies Resources: Latest PRV Fact Sheet (Updated June 2024) & Additional PRV Resources/Links & Statement
Porcine reproductive and respiratory syndrome virus continues to cause significant challenges to the US swine industry. Recent surveillance data indicates that PRRSV variant 1C.5.32, a highly virulent emerging strain, has rapidly expanded across multiple production systems and geographic regions since its initial detection in late 2023. Swine Health Information Center disease monitoring tools provide important insights into the variant’s growth, spread, and consequences in support of the National Swine Health Strategy.
Key Takeaways
▪️Industry surveillance programs continue to play a critical role in tracking the spread, evolution, and impact of 1C.5.32.
The 1C.5.32 variant, commonly associated with the 1-4-4 restriction fragment length polymorphism pattern, has become one of the most dominant wild-type PRRSV lineages circulating in the US swine herd. Due to its rapid spread and significant production impact, the SHIC-funded Morrison Swine Health Monitoring Project designated 1C.5.32 as a Variant Under Monitoring (VUM) Category 4 in August 2025. Category 4 status is reserved for variants demonstrating sustained growth and widespread dissemination, affecting more than 100 new production sites within six months.
While variant 1C.5.32 was initially detected in late 2023, it was not until August 2025 that it reached the threshold for VUM Category 4 designation. Since then, the variant has continued to expand rapidly. Although 1C.5.32 has been identified across more than 15 states, approximately 90% of cases are concentrated in Iowa and Minnesota, with nearly two-thirds of Iowa counties and one-third of Minnesota counties affected. Roughly 80% of cases have occurred in growing pig sites.
Analysis conducted through MSHMP has identified at least four distinct waves of transmission, with peaks in new cases during spring 2024, winter 2024, spring 2025, and winter 2025. Ongoing analyses of MSHMP-monitored herds have identified four significant space-time clusters. The first occurred within a 42-mile radius in central Iowa during winter 2023, followed by a 60-mile radius cluster in southern Minnesota and a 10-mile radius cluster in central Iowa during spring 2025. Most recently, a 35-mile radius cluster was detected in northeast Iowa during winter 2025.
From November 2023 through February 2026, the cumulative incidence of 1C.5.32 was estimated at 10% among growing pig sites and 6% among breeding herds. These findings underscore the rapid regional spread of the variant and highlight the critical importance of maintaining strict biosecurity protocols, particularly in growing pig populations throughout the Midwest.
Recent surveillance data underscores the continued expansion of the variant. According to the June 2026 National Surveillance Report on PRRSV VUM, 1C.5.32 remains the most significant variant currently tracked, accounting for 411 newly affected sites during the previous six months. This total far exceeds the next highest variant, 1A.13.49, which was associated with 116 new sites during the same period.
The June report identified seven PRRSV variants classified as VUM Category 2 or higher. While 1A.13.49 recently advanced to Category 4 status, 1C.5.32 remains the variant with the greatest overall impact and geographic reach. Variants 1C.5 and 1C.2 continue to meet criteria for Category 3 classification, while variants 1H.18, 1C.5.35, and 1C.2.45 are currently classified as Category 2.
Additional data from the SHIC-funded Swine Disease Reporting System further illustrates the variant’s dominance. Among all wild-type PRRSV detections reported during 2026 through June 19, the L1C.5 lineage accounted for more than 62% of detections. At the variant level, 1C.5.32 represented 44.6% of all wild-type detections, accounting for 2,205 of 4,943 cases. Across 11 states evaluated by SDRS, 1C.5.32 was the most prevalent variant in Iowa, Illinois, Kansas, Minnesota, Missouri, and Oklahoma.
Although first recognized in the Midwest, particularly in Iowa and Minnesota, 1C.5.32 has now been identified across more than 15 states and within more than 20 major swine production systems. Its widespread distribution illustrates the interconnected nature of modern swine production and reinforces the importance of surveillance, biosecurity, and rapid response measures.
Beyond its prevalence, the variant is attracting significant attention because of its association with severe production losses. Data from the PRRS Outbreak Management Program (POMP), coordinated through the Swine Disease Reporting System at Iowa State University (SHIC Domestic Swine Disease Monitoring Report), provides valuable insight into the real-world consequences of 1C.5.32 outbreaks.
POMP was established to improve understanding of the factors and management practices that influence recovery from PRRS outbreaks. The program systematically collects and analyzes outbreak data from commercial breeding herds while providing participating producers with diagnostic support, sequencing services, and benchmarking tools.
Recent POMP analyses demonstrate that outbreaks associated with 1C.5.32 result in substantially higher piglet losses than outbreaks attributed to other PRRSV lineages. One key metric used by the program is piglet losses per 1,000 sows, which measures the number of piglets not weaned during an outbreak and standardizes losses across herd sizes.
Among all POMP-enrolled outbreaks evaluated, piglet losses associated with 1C.5.32 were more than twice those observed in outbreaks caused by older L1A lineages. Median losses reached 4,761 piglets per 1,000 sows for 1C.5.32 outbreaks, compared with 2,240 piglets per 1,000 sows for L1A-associated outbreaks.
The trend remained evident when researchers compared 1C.5.32 with other variants within the same L1C.5 family. In herds classified as American Association of Swine Veterinarians status IA or IB at the time of outbreak, median piglet losses reached 3,545 piglets per 1,000 sows for 1C.5.32, approximately 19% higher than losses associated with other 1C.5 variants. Similarly, in herds with AASV II or II-vx status, median losses climbed to 5,701 piglets per 1,000 sows, roughly 32% higher than losses observed with other 1C.5 variants.
These findings suggest that the impact of 1C.5.32 extends beyond its ability to spread rapidly. Even when compared with genetically related variants, outbreaks involving 1C.5.32 appear to result in greater production losses and more severe consequences for affected breeding herds.
Recent SDRS analyses also suggest that 1C.5.32 may be diverging into two distinct genetic groups. Researchers are continuing to evaluate whether these emerging subgroups may contribute to differences in clinical presentation and production impacts observed under field conditions. Continued surveillance and sequencing efforts will be important for understanding the evolution of this variant and its implications for disease control strategies.
The continued emergence and expansion of variants such as 1C.5.32 highlight the value of coordinated surveillance efforts. Programs including MSHMP, the Swine Disease Reporting System, and POMP provide producers and veterinarians with critical information about variant distribution, disease trends, and production impacts. These tools help identify emerging threats, support informed decision-making, and strengthen industry preparedness.
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].
