Contemporary United States PRRSV 1-4-4 L1C.5 isolate causes severe disease comparable to historic highly pathogenic PRRSV

Authors: Wiarda, Jayne; Arruda, Bailey; Anderson, Tavis; Anderson, Sarah; KIM, HANJUN - Oak Ridge Institute For Science And Education (ORISE); CHANG, TYRON - Oak Ridge Institute For Science And Education (ORISE); TIDGREN HANSON, LAUREN - Oak Ridge Institute For Science And Education (ORISE); ZANELLA, ERALDO - Oak Ridge Institute For Science And Education (ORISE); Hau, Samantha; Wymore Brand, Meghan; ZHANG, JIANQIANG - Iowa State University; Devries, Alexandra

Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Porcine reproductive and respiratory syndrome virus (PRRSV) is a virus that can cause extreme illness and even death in pigs, with highly pathogenic PRRSV (HP-PRRSV) causing even more extreme sickness and death. HP-PRRSV has widespread impacts on United States farmers, agricultural industries, and the general public alike due to risks posed on animal health, agricultural economic prosperity, and food security if United States swine herd health is compromised. The United States swine industry is currently experiencing detrimental impacts due a newly emerging strain of PRRSV that has been reported to cause more severe disease. However, the degree of disease severity caused by the recently circulating virus has not yet been compared directly to historical accounts of some of the most fatal PRRSV strains. Researchers found the recent United States HP-PRRSV and a HP-PRRSV that devastated the Asian swine industry in 2006 cause highly similar extreme sickness and death in pigs. Findings establish that currently circulating PRRSV strains pose an imminent threat to United States swine herds with the potential to cause extreme disease alike to historical HP-PRRSV outbreaks in Asia if not further addressed.

Technical Abstract: Porcine reproductive and respiratory syndrome virus (PRRSV) is a major economic and animal health burden on the United States swine industry due to morbidity- and mortality-associated losses affecting all stages of pig production. Currently, a large proportion of losses are attributed to a highly virulent PRRSV strain, referred to here as L1C.5. A field-relevant contemporary L1C.5 isolate was characterized in pigs to assess disease kinetics in comparison to a moderately virulent PRRSV strain that emerged in the United States in the early 2000s (MN184), and a highly pathogenic PRRSV (HP-PRRSV) strain that devasted Asian swine industries beginning in 2006 (JXwn06). Weaned pigs were inoculated with PRRSV JXwn06, L1C.5, MN184, or mock inoculum and necropsied at 2, 6, and 10 days post-inoculation or as needed due to severe disease. Clinical metrics, viral loads, cytokine concentrations, antibody concentrations, and pathology were compared between groups to assess pathogenicity. JXwn06 and L1C.5 animals developed more severe disease that diverged from MN184 and mock animals. Disease dynamics were also highly similar between JXwn06 and L1C.5 groups. Results demonstrate that despite unique genetics, geographical origins, and dates of emergence a contemporary United States-endemic PRRSV (L1C.5) can cause severe disease comparable to a HP-PRRSV (JXwn06) that devastated the Asian swine industry nearly two decades ago. Identifying the common features that contribute to increased virulence of diverse HP-PRRSV strains will be essential for tailoring better PRRSV control methods, especially for contemporary PRRSV strains that pose imminent threats to swine health in North America.