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Location: Virus and Prion Research

Title: Novel reassortant human-like H3N2 and H3N1 influenza A viruses detected in pigs are virulent and antigenically distinct from swine viruses endemic to the United States

item RAJAO, DANIELA - Non ARS Employee
item GAUGER, PHILLIP - Iowa State University
item Anderson, Tavis
item LEWIS, NICOLA - University Of Cambridge
item ABENTE, EUGENIO - Orise Fellow
item KILLIAN, MARY LEA - Animal And Plant Health Inspection Service (APHIS)
item PEREZ, DANIEL - University Of Georgia
item SUTTON, TROY - University Of Maryland
item ZHANG, JIANQIANG - Iowa State University
item Vincent, Amy

Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/2015
Publication Date: 11/15/2015
Citation: Rajao, D.S., Gauger, P.C., Anderson, T.K., Lewis, N.S., Abente, E.J., Killian, M.L., Perez, D.R., Sutton, T.C., Zhang, J., Vincent, A.L. 2015. Novel reassortant human-like H3N2 and H3N1 influenza A viruses detected in pigs are virulent and antigenically distinct from swine viruses endemic to the United States. Journal of Virology. 89(22):11213-11222.

Interpretive Summary: Pigs can be infected with influenza A viruses (IAV) from multiple species, and thus serve as intermediary hosts in the evolution of influenza. The frequent human-to-swine transmission has greatly contributed to the diversity of IAV in swine populations around the globe. Novel human-like H3N2 and H3N1 viruses were recently detected in pigs by the USDA surveillance system from 2012 and 2014. The human-like H3N2 and H3N1 contained genes from human seasonal H3N2, classical swine H1N1, and H1N1pdm09 viruses. The novel viruses efficiently infected pigs and resulted in onward airborne transmission to indirect contacts and caused respiratory disease and significant lung pathology in infected pigs. Importantly, the novel H3N2 and H3N1 were not efficiently recognized by immunity to contemporary U.S. H3N2 swine viruses and from the strains used in commercially available swine vaccines. Consequently, pigs likely have limited immune protection against these novel human-like viruses, which could have a significant impact on the swine industry.

Technical Abstract: Since November of 2012, human-like swine H3 influenza A viruses have been detected by the USDA surveillance system. Here, we genetically and antigenically characterized two of the novel swine human-like H3N2 and H3N1 viruses detected in the same herd but two years apart. Their pathogenicity and transmission in pigs were compared to a human H3N2 with common hemagglutinin (HA) ancestry. The HA of the two selected swine human-like H3N2 and H3N1 viruses were similar to contemporary human seasonal H3 strains and their internal genes closely related to 2009 H1N1 pandemic viruses (H1N1pdm09). The NA of the H3N2 was of the contemporary human N2 lineage, while the H3N1 had the NA of the classical swine N1 lineage. Both viruses were antigenically distant from all swine H3 viruses that currently circulate in the U.S. with important implications for control by current vaccines. The swine human-like H3 viruses also showed antigenic drift from human seasonal H3N2 strains. Both swine human-like viruses infected and replicated in pigs, caused lung pathology, and transmitted to indirect contacts. These results indicate that these novel H3 viruses are fully virulent and can sustain onward transmission in pig populations. Importantly, their HA are distinct from IAV currently circulating in swine and from human and swine vaccine strains. Consequently, this virus could have a significant impact on the swine industry if it expands to cause more widespread outbreaks.