Abstract
We isolated an influenza strain named A/Swine/Fujian/F1/2010 (H1N2) from a pig suspected to be infected with swine flu. The results of electron microscopy, hemagglutination (HA) assay, hemagglutination inhibition (HI) assay, and whole genome sequencing analysis suggest that it was a reassortant virus of swine (H1N1 subtype), human (H3N2 subtype), and avian influenza viruses. To further study the genetic evolution of A/Swine/Fujian/F1/2010 (H1N2), we cloned its whole genome fragments using RT-PCR and performed phylogenetic analysis on the eight genes. As a result, the nucleotide sequences of HA, NA, PB1, PA, PB2, NP, M, and NS gene are similar to those of A/Swine/Shanghai/1/2007(H1N2) with identity of 98.9%, 98.9%, 99.0%, 98.6%, 99.0%, 98.9%, 99.3%, and 99.3%, respectively. Similar to A/Swine/Shanghai/1/2007(H1N2), we inferred that the HA, NP, M, and NS gene fragments of A/Swine/Fujian/F1/2010 (H1N2) strain were derived from classical swine influenza H3N2 subtype, NA and PB1 were derived from human swine influenza H3N2 subtype, and PB2 and PA genes were derived from avian influenza virus. This further validates the role of swine as a “mixer” for influenza viruses.
Highlights
Swine influenza is an acute and highly contagious flu caused by swine influenza virus (SIV), which infects human and pigs
EDS-76 and ND were positive sera provided by Fujian Institute of Animal Husbandry and Veterinary Medicine; the standard antigens and its antisera of H1, H3, H5, H7, and H9 subtypes and antisera of N1, N2, and N9 subtypes were purchased from Harbin Veterinary Research Institute; RNA extraction kit Trizol, plasmid extraction kit, LATaq DNA polymerase, RNasin Inhibition, M-MLV, dNTP, BamHI, HindIII, and PMD18-T vector were purchased from Dalian Bao Biological Company; Escherichia coli engineering strain DH5a was preserved by our laboratory
BALB/c mice were collected from Fujian Medical Laboratory Animal Center; 5-week-old piglets were purchased from a large-scale pig farm in Fuzhou, which were confirmed to be negative in serological antibody examination; SPF eggs were purchased from Fuzhou Dabei Agricultural Biotechnology Co. and incubated to 9 to 11 days of age
Summary
Swine influenza is an acute and highly contagious flu caused by swine influenza virus (SIV), which infects human and pigs. The 8 genomic segments of different influenza viruses can be randomly shuffled to generate new reassortant viruses [3]. As pigs possess both NeuAc-2,3Gal and NeuAc-2,6Gal receptors, they can infect both human and avian influenza viruses [3]. Pigs become a “mixer” for reassortment of influenza viruses and an “incubator” for emergence of new influenza strains [4, 5]. Two out of the four most serious influenza pandemics in the history are caused by reassortment of gene segments from avian influenza viruses [8, 9]
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