| Pigs have been regarded as the important intermediate hosts and “mixing vessel†of influenza A viruses. Co-infections in pigs promote frequent gene recombination of different subtypes and sources of influenza viruses and continuously generate novel prevalent strains. Since the 20 th century to date, there have been four human influenza pandemics occurred globally, and all of them are closely related to swine influenza viruses(SIVs). In recent years, various subtypes and variable SIVs have been prevalent among pigs. Since the initial report in 1979, Eurasian avian-like H1N1(EA H1N1) SIVs have become the predominant strains and already established a stable genetic lineage in China. Because EA H1N1 SIV not only infects pigs but also humans, it poses a serious threat for the public health security. Although many studies have elucidated the epidemiology of EA H1N1 SIVs, the biological characteristics of EA H1N1 SIVs are largely unknown. Therefore, it will be significant to illustrate the biological characteristics of EA H1N1 SIVs.From August 2010 to March 2013, we performed extensive influenza viruses surveillance in pigs in China. Eventually, we isolated and identified 139 EA H1N1 SIVs and selected some of them to evaluate the pathogenicity, receptor-binding preference, and transmissibility in mammals. First, we investigated the pathogenicity in BALB/c of three representative EA H1N1 SIVs and one previously isolated strain. The results showed that all the four EA H1N1 SIVs were low virulent to mice and mainly replicated in respiratory. Then, we tested the receptor-binding specificity of two EAH1N1 SIVs in mice experiment by using a solid-phase binding assay with four different glycans and analyzed the amino acid differences with Megalign. The results indicated that two EA H1N1 SIVs preferentially bound to α-2,6–linked SAs, which was the prerequisite for respiratory droplet transmissibility between mammals, and there were 33 amino acid differences between two strains. Furthermore, we evaluated the respiratory droplet transmissibility of the above two EA H1N1 SIVs in ferrets,and found that both of them transmitted to various degrees. More importantly, the A / swine / Guangxi / 18/2011(H1N1) could transmit efficiently by respiratory droplet between ferrets.The results of this study had important implications for us in understanding the biological properties and pandemic potential of the EA H1N1 SIVs. Meanwhile, it laid foundation to further explore the molecular mechanism of EA H1N1 SIVs respiratory droplet transmissibility between mammals and provided theoretical basis to prevent and control the EA H1N1 SIVs. |
