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The PRRSV Variants Under Monitoring (VUMs) Monthly Report, in collaboration with the SHIC-funded Morrison Swine Health Monitoring Project (MSHMP) and the PRRS-Loom analytical platform, was launched in August 2025. The report is designed to give producers and veterinarians an early warning of potential threats, improving preparedness and coordinated response across the industry.
This initiative utilizes the PRRS-Loom tool, a machine-learning model that analyzes 603 ORF5 bases to classify viruses by lineage, sublineage, and variants. These classifications are combined with a forecasting algorithm that anticipates whether a variant is likely to expand significantly, defined as more than a 20% increase in the next year, based on retrospective data with 77% accuracy. When integrated with the near real-time MSHMP data, the approach allows the new report to identify where specific PRRSV variants are already present and estimate their potential for wider spread.
PRRSV variants are defined as closely related viruses based on ORF5 gene similarity, typically differing less than 2.5% within a variant and 5% from the nearest related variant. VUMs specifically represent PRRSV-2 variants circulating in the US that show genetic and epidemiologic indicators of wider transmission. To highlight urgency and guide responses, VUMs are categorized into four levels according to the number of sites impacted over the past six months:
- Level 1 involves up to 30 sites
- Level 2 involves 31–50 sites
- Level 3 involves 51–100 sites
- Level 4 involves >100 sites
Reports for Level 2 or higher VUMs will include expanded epidemiological discussion, examining affected sequences, sites, systems, and states. These summaries will be accompanied by epidemiological curves showing variant dynamics over time and situation reports that provide context for ongoing industry response. Together, these tools give stakeholders greater situational awareness, helping veterinarians and producers adjust strategies before a variant reaches wider distribution.
This information will be broadly accessible and focused on actionable information for producers. The VUM reports will be circulated to MSHMP participants, shared in SHIC’s monthly e-newsletter, and made publicly available on both the MSHMP website and the PRRS-Loom platform.
September 4, 2025/ Swine Health Information Center/ United States.
https://www.swinehealth.org
