1. Institute of Zoology and Graduate School, Chinese Academy of Sciences, Beijing 100080
2. State Key Laboratory of Emerging Infectious Diseases, Department of Microbiology, The University of Hong Kong, Faculty of Medicine Building, 21 Sassoon Road, Pokfulam, Hong Kong SAR
3. Department of Microbiology and Immunology, Guangxi Medical University
4. Guangxi Center for Disease Control and Prevention, Nanning 530021, People's Republic of China