Evidence for Cross-species Influenza A Virus Transmission within Swine Farms, China

Abstract

Background. Our understanding of the risk factors for swine Influenza A virus transmission between humans and pigs is sparse. Methods. Beginning in 2015, we used a One Health approach and serial sampling to prospectively study 299 swine workers and 100 controls, their 9000 pigs, and six pig farm environments in China for Influenza A viruses (IAVs) using molecular, culture, and immunological techniques. Study subjects were closely monitored for infuen-za-like illness (ILI) events. Results. Upon enrollment, swine workers had higher serum neutralizing antibody titers against swine H1N1 and higher nasal wash total IgA and specifc IgA titers against swine H1N1 and H3N2 viruses. Over a period of 12 months, IAVs were detected by qRT-PCR in 52 (12%) of 432 environmental swabs, 275 (7.6%) of 3600 pig oral secretion, 25 (5.8%) of 432 water, 24 (5.5%) of 432 aerosol, and 20 (4.6%) of 432 fecal-slurry specimens. Five (15.6%) of 32 subjects with ILI events had nasopharyngeal swab specimens that were positive for IAV and 17 (53%) demonstrated 4-fold rises in neutralization titers against a swine virus. Reassorted Eurasian avian-like swine H1N1, pdm09(H1N1)-like virus, and swine-like H3N2 viruses were identified in pig farms. The H1N1 viruses were nearly genetically identical with the human H1N1 viruses isolated from the subjects with ILI. Conclusion. There was considerable evidence of A(H1N1)pdm09-like, swine H1N1 and swine H3N2 viruses reassorting and circulating within the pig farms and crossing species. These data suggest that stronger surveillance for novel Influenza virus emergence within swine farms is imperative.