1. 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 730000, China
2. College of Agriculture, Ningxia University, Yinchuan 750021, China
3. Animal Pathology Laboratory, College of Veterinary Medicine, Northwest A&F University, Xianyang 712100, China
4. State Key Laboratory of Veterinary Etiological Biology, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou 730046, China