Pathogenesis and transmission of a reassorted H1 influenza A virus detected in North American swine

Background: The USDA influenza A virus in swine national surveillance plan identified an increase in the detection frequency of a group of swine 1A.1.1.3 hemagglutinin (HA) clade viruses. This change was associated with reassortment events that resulted in new neuraminidase (NA) gene pairings. We hypothesized that the new N1 genes improved the transmission efficiency of the virus. Methods: We assessed the pathogenesis and transmission of four H1 1A.1.1.3 swine strains paired with different NA subtypes and lineages, all of which shared similar internal gene constellations. Results: There was little variation in the titers of viral nasal shedding across the groups, and the different surface protein pairings had no effect on transmission efficiency. All IAV strains, reflecting both pre- and post-reassortment genetic patterns, were transmitted to naïve contact pigs. Conclusions: These data indicate that the combinations of 1A.1.1.3 HA with NA subtypes had little impact on transmission. These findings suggest that the observed increased detection frequency of the H1 1A.1.1.3 clade in the U.S. likely resulted from a decrease in population immunity derived from differential vaccine or prior exposure and/or variations in production practices and ecological conditions rather than a gain of replication or transmission efficiency. Supplementary Material File (manuscript.docx) - Download - 1.02 MB Information & Authors Information Version history Peer review timeline Published Influenza and Other Respiratory Viruses Version of Record19 Feb 2026Published Copyright This work is licensed under a Non Exclusive No Reuse License.

Authors Metrics & Citations Metrics Article Usage 245views 166downloads Citations Download citation Débora B. Goulart, Carine K. Souza, Giovana Ciacci Zanella, et al. Pathogenesis and transmission of a reassorted H1 influenza A virus detected in North American swine. Authorea. 29 August 2025. DOI: https://doi.org/10.22541/au.175648074.48873102/v1 DOI: https://doi.org/10.22541/au.175648074.48873102/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu.