Geographic Distribution and ORF5 Diversity of PRRSV-2 Variants in Midwestern U.S. Diagnostic Submissions, 2023-2025

Porcine reproductive and respiratory syndrome (PRRS) is a serious disease that causes reproductive failure and late abortion in breeder farms, as well as severe respiratory manifestations in pigs of all ages. In the United States, the swine industry has been affected by PRRSV-2, particularly due to control challenges and the virus's ongoing evolution. In this study, we conducted a genetic characterization of the 642 PRRSV-2 ORF5 sequences generated from diagnostic submissions at the Animal Disease Research and Diagnostic Laboratory (ADRDL) at South Dakota State University (SDSU). These sequences were generated over a 3-year period from 2023 through 2025, with 208 (32.4%), 130 (20.2%), and 304 (47.4%) sequences in 2023, 2024, and 2025, respectively. These sequences were from swine diagnostic submissions from ten states in the Midwest, including Minnesota (MN; 350/642, 54.5%), South Dakota (SD; 182/642, 28.3%), and Iowa (IA; 73/642, 11.4%), collectively accounting for 94.2% of submitted sequences. The genetic typing revealed that the L1C sub-lineage was the most frequently detected among the submitted sequences, accounting for around 60%, with L1C.5 as the major contributor (371/642). Other sub-lineages, such as L5A, L1A, L1D, and L1H, were also detected, but in smaller numbers. More than 80% of the detected sequences were classified as wild-type or wild-like based on ORF5 identity to commercial vaccine reference strains. Interestingly, this study documented increased detection of the recently reported L1C.5.32 variant, which was the most frequently detected variant in 2025 (123 detections), particularly in Minnesota. Moreover, L1C.5.34, L1C.5.36, L1C.3.25, and L1C.2 variants were also detected, and the L1H.18 variant showed increased detection, especially in 2025. In conclusion, this study provides genetic characterization of PRRSV-2 ORF5 sequences from Midwestern U.S. diagnostic submissions (a key U.S. swine production region), submitted to the SDSU ADRDL.