1. College of Veterinary Medicine, China Agricultural University, Beijing 100094, China.
2. Institute of Microbiology, Chinese Academy of Sciences, Beijing 100080, China.
3. Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.
4. Graduate School, Chinese Academy of Sciences, Beijing, China.
5. Institute of Microbiology and Epidemiology, Academy of Military Medical Sciences, Beijing 100071, China.