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ARS Home » Midwest Area » Ames, Iowa » National Animal Disease Center » Virus and Prion Research » Research » Publications at this Location » Publication #387474

Research Project: Intervention Strategies to Control Influenza A Virus Infection in Swine

Location: Virus and Prion Research

Title: Human-to-swine transmission and subsequent evolution of H1N1 pandemic 2009 lineage influenza A viruses in US swine

item MARKIN, ALEXEY - Orise Fellow
item ARENDSEE, ZEBULUN - Orise Fellow
item GAUGER, PHILLIP - Iowa State University
item Baker, Amy
item Anderson, Tavis

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 9/20/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The 2009 H1N1 pandemic (pdm09) lineage of influenza A viruses (IAVs) became endemic and entirely replaced the pre-2009 seasonal H1N1 in humans. Notably, the pdm09 lineage is a unique IAV lineage that can easily cross the human and swine interspecies barriers, and causing incursions and influenza outbreaks in swine every year after its original appearance. Following a human-to-swine spillover, the pdm09 viruses often mutated and reassorted with other co-circulating swine IAVs, thus creating an opportunity for reverse-spillovers from swine to humans. We examined the IAV detection statistics for seasons between 2011-12 and 2019-20 and found a strong correlation between the number of detections of human and swine pdm09 infections across seasons. Additionally, using phylogenetic analysis we demonstrated that most US swine pdm09 infections were caused by human-to-swine spillovers that occurred in the same flu season as the swine infections, suggesting that human pdm09 transmission ‘fuels’ the transmission of pdm09 in pigs. However, the 2020-21 flu season did not follow this pattern. Despite the relative absence of influenza circulation in humans in the US, we observed many pdm09 cases in swine (one of the highest detection numbers since 2009). Using genomic and phylogenetic analyses we found that the vast majority of recent (2020-21) pdm09 detections in swine originated from the prior season, 2019-20 human-to-swine spillovers. Further, we found that 5 genetically characterized pdm09 detections in humans in 2020-21 were likely associated with swine-to-human IAV transmission of the onward circulating pdm09 in pigs. This unique dynamic suggests that 2019-20 pdm09 viruses obtained novel properties compared to 2017-18 or 2018-19 flu seasons, thus causing more frequent and sustained pdm09 outbreaks in the US swine population that also possess the propensity to cross back into humans.