Philippe Noriel Q. Pascuaa,1, Min-Suk Songa,1, Jun Han Leea, Yun Hee Baeka, Hyeok-il Kwona, Su-Jin Parka, Eun Hye Choia, Gyo-Jin Lima, Ok-Jun Leea, Si-Wook Kima, Chul-Joong Kimb, Moon Hee Sungc, Myung Hee Kimd, Sun-Woo Yoone, Elena A. Govorkovae, Richard J. Webbye, Robert G. Webstere,2, and Young-Ki Choia,2
aCollege of Medicine and Medical Research Institute, Chungbuk National University, Cheongju 361-763, Republic of Korea;
bCollege of Veterinary Medicine, Chungnam National University, DaeJeon 305-764, Republic of Korea;
cBioleaders Corporation, DaeJeon 305-500, Republic of Korea;
dDivision of Biosystems Research, Korea Research Institute of Bioscience and Biotechnology, DaeJeon 305-806, Korea; and
eDivision of Virology, Department of Infectious Diseases, St. Jude Children’s Research Hospital, Memphis, TN 38105
Efficient worldwide swine surveillance for influenza A viruses is urgently needed; the emergence of a novel reassortant pandemic H1N1 (pH1N1) virus in 2009 demonstrated that swine can be the direct source of pandemic influenza and that the pandemic potential of viruses prevalent in swine populations must be monitored. We used the ferret model to assess the pathogenicity and transmissibility of predominant Korean triple-reassortant swine (TRSw) H1N2 and H3N2 influenza viruses genetically related to North American strains. Although most of the TRSw viruses were moderately pathogenic, one [A/Swine/Korea/1204/2009; Sw/1204 (H1N2)] was virulent in ferrets, causing death within 10 d of inoculation, and was efficiently transmitted to naive contact ferrets via respiratory droplets. Although molecular analysis did not reveal known virulence markers, the Sw/1204 virus acquired mutations in hemagglutinin (HA) (Asp-225-Gly) and neuraminidase (NA) (Ser-315-Asn) proteins during the single ferret passage. The contact-Sw/1204 virus became more virulent in mice, replicated efficiently in vitro, extensively infected human lung tissues ex vivo, and maintained its ability to replicate and transmit in swine. Reverse-genetics studies further indicated that the HA225G and NA315N substitutions contributed substantially in altering virulence and transmissibility. These findings support the continuing threat of some field TRSw viruses to human and animal health, reviving concerns on the capacity of pigs to create future pandemic viruses. Apart from warranting continued and enhanced global surveillance, this study also provides evidence on the emerging roles of HA225G and NA315N as potential virulence markers in mammals.
severe disease, interspecies transmission, evolution, viral segments
1P.N.Q.P. and M.-S.S. contributed equally to this work.
2To whom correspondence may be addressed.
Author contributions: P.N.Q.P., M.-S.S., and Y.K.C. designed research; P.N.Q.P., M.-S.S., J.H.L., Y.H.B., H.-i.K., S.-J.P., E.H.C., G.-J.L., O.-J.L., S.-W.K., M.H.S., M.H.K., S.-W.Y., and E.A.G. performed research; C.-J.K., E.A.G., R.G.W., and Y.K.C. contributed new reagents/analytic tools; P.N.Q.P., M.-S.S., M.H.K., S.-W.Y., E.A.G., R.J.W., R.G.W., and Y.K.C. analyzed data; and P.N.Q.P., M.-S.S., E.A.G., R.J.W., R.G.W., and Y.K.C. wrote the paper.