Location: Virus and Prion ResearchTitle: Human-to-swine spillovers of H3N2 influenza A virus detected in United States pigs in 2018-2019
|POWELL, JOSHUA - Orise Fellow
|ZELLER, MICHAEL - Iowa State University
|GAUGER, PHIL - Iowa State University
Submitted to: American Society for Virology Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 4/1/2021
Publication Date: 7/21/2021
Citation: Powell, J.D., Zeller, M.A., Gauger, P.C., Anderson, T.K., Vincent, A.L. 2021. Human-to-swine spillovers of H3N2 influenza A virus detected in United States pigs in 2018-2019 [abstract]. American Society for Virology Meeting. Talk no. W21-6.
Technical Abstract: In 2019, there were four influenza A virus (IAV) H3 detections from the human seasonal 3c3.A clade in U.S. pigs in Michigan, Illinois and Virginia. Whole genome sequencing of these strains revealed all eight gene segments were most similar to 2018-2019 H3N2 human seasonal influenza. To evaluate the viral kinetics, pathogenesis and transmission of these human-to-swine spillovers, we characterized A/Swine/Virginia/A02478738/2019(H3N2) (SW/VA/19) in cell culture and in experimentally infected pigs. In vitro viral kinetics demonstrated that SW/VA/19 replicated to moderate titers in swine respiratory cells at a physiologically relevant swine body temperature of 40 °C. Conversely, three H3N2 human seasonal strains tested under the same conditions had significantly lower titers suggesting that SW/VA/19 was adapted to swine. In pigs, SW/VA/19 was shed in nasal secretions and transmitted to all indirect contact pigs placed in a neighboring pen; whereas a representative human seasonal strain A/Switzerland/9715293/2013(H3N2) from the 3c3.A clade failed to transmit to indirect contact swine. In contrast to the observed efficient transmission, SW/VA/19 induced minimal macroscopic and microscopic lesions, suggesting low virulence in swine. While no additional spillovers or detections of onward circulation of these human-like H3N2 viruses were reported in swine in the last 14 months, these results suggest that viruses similar to SW/VA/19 may not have required reassortment with endemic swine IAV gene segments to facilitate infection and transmission. However, limited detection suggests a yet unknown restriction interfering with persistence and onward transmission of these human-like H3N2 viruses to other herds. Genetic similarities and differences of these human-like H3N2 detections in swine were compared to seasonal H3N2 circulating in humans during the 2018-2019 flu season to understand why these viruses infected and transmitted in swine, but as of yet, failed to become endemic in the U.S. pig population.