1 National Research Center For Wildlife Born Diseases, Key Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China; 
2 Graduate University of Chinese Academy of Sciences, Beijing 100049, China; 
3 College of Life Science, Hebei Normal University, Shijiazhuang 050016, China

Subtypes of H1N1 influenza virus can be found in humans in North America, while they are also asso- ciated with the infection of swine. Characterization of the genotypes of viral strains in human popula- tions is important to understand the source and distribution of viral strains. Genomic and protein se- quences of 10 isolates of the 2009 outbreak of influenza A (H1N1) virus in North America were obtained from GenBank database. To characterize the genotypes of these viruses, phylogenetic trees of genes PB2, PB1, PA, HA, NP, NA, NS and M were constructed by Phylip3.67 program and N-Linked glycosylation sites of HA, NA, PB2, NS1 and M2 proteins were analyzed online by NetNGlyc1.0 program. Phylogenetic analysis indicated that these isolates are virtually identical but may be recombinant vi- ruses because their genomic fragments come from different viruses. The isolates also contain a char- acteristic lowly pathogenic amino acid motif at their HA cleavage sites (IPSIQSR↓GL), and an E residue at position 627 of the PB2 protein which shows its high affinity to humans. The homologous model of M proteins showed that the viruses had obtained the ability of anti-amantadine due to the mutation at the drug-sensitive site, while sequence analysis of NA proteins indicated that the viruses are still suscep- tible to the neuraminidase inhibitor drug (i.e. oseltamivir and zanamivir) because no mutations have been observed. Our results strongly suggested that the viruses responsible for the 2009 outbreaks of influenza A (H1N1) virus have the ability to cross species barriers to infect human and mammalian animals based on molecular analysis. These findings may further facilitate the therapy and prevention of possible transmission from North America to other countries.

Supported by the National Key Basic Research and Development Program of China (Grant No. 2007BC109103), Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No. KSCX2-YW-N-063) and National Natural Science Founda-tion of China (Grant No. 30671576)