Aerosol Transmission from Infected Swine to Ferrets of an H3N2 Virus Collected from an Agricultural Fair and Associated with Human Variant Infections

Abstract

A recently emerged lineage of human-like H3N2 (H3.2010.1) influenza A virus (IAV) from swine has been frequently detected in commercial and exhibition swine in recent years and has been associated with H3N2 variant cases in humans from 2016 and 2017. To demonstrate a model for characterizing the potential for zoonotic transmission associated with swine IAV, we performed an in vivo study of transmission between pigs infected with an H3.2010.1 H3N2 IAV and aerosol contact ferrets. The efficient interspecies transmission demonstrated for the H3.2010.1 IAV in swine emphasizes the need for further characterization of viruses circulating at the swine-human interface for transmission potential prior to human spillover and the development and implementation of more robust vaccines and control strategies to mitigate human exposure to higher-risk swine strains. Influenza A viruses (IAV) sporadically transmit from swine to humans, typically associated with agricultural fairs in the United States. A human seasonal H3 virus from the 2010-2011 IAV season was introduced into the U.S. swine population and termed H3.2010.1 to differentiate it from the previous swine H3 virus. This H3N2 lineage became widespread in the U.S. commercial swine population, subsequently spilling over into exhibition swine, and caused a majority of H3N2 variant (H3N2v) cases in humans in 2016 and 2017. A cluster of human H3N2v cases were reported at an agricultural fair in 2017 in Ohio, where 2010.1 H3N2 IAV was concurrently detected in exhibition swine. Genomic analysis showed that the swine and human isolates were nearly identical. In this study, we evaluated the propensity of a 2010.1 H3N2 IAV (A/swine/Ohio/A01354299/2017 [sw/OH/2017]) isolated from a pig in the agricultural fair outbreak to replicate in ferrets and transmit from swine to ferret. sw/OH/2017 displayed robust replication in the ferret respiratory tract, causing slight fever and moderate weight loss. Further, sw/OH/2017 was capable of efficient respiratory droplet transmission from infected pigs to contact ferrets. These findings establish a model for evaluating the propensity of swine IAV to transmit from pig to ferret as a measure of risk to the human population. The identification of higher-risk swine strains can then be targeted for control measures to limit the dissemination at human-swine interfaces to reduce the risk of zoonotic infections and to inform pandemic planning. IMPORTANCE A recently emerged lineage of human-like H3N2 (H3.2010.1) influenza A virus (IAV) from swine has been frequently detected in commercial and exhibition swine in recent years and has been associated with H3N2 variant cases in humans from 2016 and 2017. To demonstrate a model for characterizing the potential for zoonotic transmission associated with swine IAV, we performed an in vivo study of transmission between pigs infected with an H3.2010.1 H3N2 IAV and aerosol contact ferrets. The efficient interspecies transmission demonstrated for the H3.2010.1 IAV in swine emphasizes the need for further characterization of viruses circulating at the swine-human interface for transmission potential prior to human spillover and the development and implementation of more robust vaccines and control strategies to mitigate human exposure to higher-risk swine strains.