1. Institute for Advanced Research, Cixi Biomedical Research Institute, Wenzhou Medical University, Zhejiang 325035, P. R. China
2. State Key Laboratory for Animal Disease Control and Prevention, College of Veterinary Medicine, Lanzhou University, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou 730046, P. R. China
3. College of Life Science and Technology, Gansu Agricultural University, Lanzhou 730070, P. R. China