1. State Key Laboratory for Animal Disease Control and Prevention, Chinese Academy of Agricultural Sciences, Lanzhou 730046, China
2. Ministry of Agriculture Key Laboratory of Veterinary Public Health, Chinese Academy of Agricultural Sciences, Lanzhou 730046, China
3. Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou 730046, China
4. School of Public Health, Lanzhou University, Lanzhou 730000, China