1. Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary MedicineChina Agricultural University Beijing 100193 China
2. Institute of Animal Husbandry and Veterinary MedicineFujian Academy of Agricultural Sciences Fuzhou 350013 Fujian China
3. College of Veterinary MedicineHuazhong Agricultural University Wuhan 430070 Hubei China