Department of Pathogenic Biology, The Fourth Military Medical University, Xian, 710032, P. R. China. zhaoya@fmmu.edu.cn.|Department of Pathogenic Biology, The Fourth Military Medical University, Xian, 710032, P. R. China. zhaoya@fmmu.edu.cn.|Department of Pathogenic Biology, The Fourth Military Medical University, Xian, 710032, P. R. China. zhaoya@fmmu.edu.cn.|Department of Pathogenic Biology, The Fourth Military Medical University, Xian, 710032, P. R. China. zhaoya@fmmu.edu.cn.|Department of Pathogenic Biology, The Fourth Military Medical University, Xian, 710032, P. R. China. zhaoya@fmmu.edu.cn.|Department of Pathogenic Biology, The Fourth Military Medical University, Xian, 710032, P. R. China. zhaoya@fmmu.edu.cn.|Department of Pathogenic Biology, The Fourth Military Medical University, Xian, 710032, P. R. China. zhaoya@fmmu.edu.cn.|Department of Pathogenic Biology, The Fourth Military Medical University, Xian, 710032, P. R. China. zhaoya@fmmu.edu.cn.