1. College of Veterinary Medicine,Hebei Agricultural University,Baoding 071001,China
2. State Key Laboratory for Animal Disease Control and Prevention,Harbin Veterinary Research Institute,Chinese Academy of Agricultural Sciences,Harbin 150069,China;College of Veterinary Medicine,Xinjiang Agricultural University,Urumqi 830052,China
3. State Key Laboratory for Animal Disease Control and Prevention,Harbin Veterinary Research Institute,Chinese Academy of Agricultural Sciences,Harbin 150069,China