Objective It is by way of using the wild-type virus in studying biological characteristics of virus and mechanism in interaction between virus and its receptor cells in virology research,but prerequiste for this type of virus should be obtained by culturing in vitro and with a low infectiousness as well as not endangered personal safety and natural enveronment. However,some viruses,such as H7N9,H5N1,SARS,HCV,EBV etc,are very difficult in cultivation in vitro and manipulation of them must be confined in bios...