U.S. feral swine were exposed to both avian and swine influenza A viruses

Authors: MARTIN, BRIGITTE - Mississippi State University; SUN, HAILIANG - Mississippi State University; CARREL, MARGARET - University Of Iowa; CUNNINGHAM, FRED - Animal And Plant Health Inspection Services (APHIS), National Wildlife Center; BAROCH, JOHN - Animal And Plant Health Inspection Services (APHIS), National Wildlife Center; HANSON-DORR, KATIE - Animal And Plant Health Inspection Services (APHIS), National Wildlife Center; YOUNG, SEAN - University Of Arkansas; SCHMIT, BRANDON - Animal And Plant Health Inspection Services (APHIS), National Wildlife Center; NOLTING, JACQUELINE - The Ohio State University; YOON, KYOUNG-JIN - Iowa State University; Lager, Kelly

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/2017
Publication Date: 10/1/2017
Citation: Martin, B.E., Sun, H., Carrel, M., Cunningham, F.L., Baroch, J.A., Hanson-Dorr, K.C., Young, S.G., Schmit, B., Nolting, J.M., Yoon, K-J., Lutman, M.W., Pedersen, K., Lager, K., Bowman, A.S., Slemons, R.D., Smith, D.R., DeLiberto, T., Wan, X-F. 2017. Feral swine in the United States have been exposed to both avian and swine influenza A viruses. Applied and Environmental Microbiology. 83(19):e01346-17.

Interpretive Summary: There are more than 5 million feral swine distributed across at least 35 states in the United States. In contrast to domestic swine, feral swine are free ranging and have unique opportunities for contact with wildlife and livestock which can lead to feral swine being an intermediate for disease transmission. The ecology of influenza A viruses (IAVs) is complex. Although the virus is capable of infecting many species, how it jumps or transmits between species is poorly understood. Moreover, animals or birds infected with more than one IAV can produce a novel virus that may lead to new epidemics in the host and other species. Swine are susceptible to both avian and mammalian IAV and can serve as an IAV “mixing vessel” that might produce unique viruses that cause disease in swine and even humans. To gain a better understanding of the potential role of feral swine in the ecology of IAV, a study was completed testing blood samples from feral swine for IAV antibodies. Although at a low frequency, results indicate that feral swine in the United States have been exposed to influenza A viruses (IAVs) that are consistent with those found in both domestic swine and wild birds, with the predominant infections consisting of swine adapted IAVs. This suggests feral swine could serve as hosts for the generation of novel IAVs at the interface of feral swine, wild birds, domestic swine, and humans.

Technical Abstract: Influenza A viruses (IAVs) in swine can cause sporadic infections and pandemic outbreaks among humans, but how avian IAV emerges in swine is still unclear. Unlike domestic swine, feral swine are free ranging and have many opportunities for IAV exposure through contacts with various habitats and animals, including migratory waterfowl, a natural reservoir for IAVs. During 2010–2013, 8,239 serum samples were collected from feral swine across 35 US states and tested against 45 contemporary antigenic variants of avian, swine, and human IAVs; of these, 406 (4.9%) samples were IAV-antibody positive. Among 294 samples selected for antigenic characterization, 271 cross-reacted with =1 testing virus whereas the other 23 did not cross-react with any testing virus. Of the 271 IAV-positive samples, 236 cross-reacted with swine IAVs, 1 with avian IAVs, and 16 with avian and swine IAVs, indicating that feral swine were exposed to both swine and avian IAVs but predominantly to swine IAVs. Our findings suggest that feral swine could potentially be infected with both avian and swine IAVs, generating novel IAVs by hosting and reassorting IAVs from wild birds and domestic swine and facilitating adaptation of avian IAVs to other hosts, including humans, before their spillover. Continued surveillance to monitor the distribution and antigenic diversities of IAVs in feral swine is necessary to increase our understanding of the natural history of IAVs.