1. State Key Laboratory for Agro-Biotechnology, College of Biological Science, China Agricultural University, Beijing, People's Republic of China
2. Key Laboratory of Medical Molecular Virology of MOH and MOE, Fudan University Shanghai Medical College, Shanghai, People's Republic of China
3. College of Veterinary Medicine, China Agricultural University, Beijing, People's Republic of China
4. Department of Microbiology and Immunology, College of Medicine, University of Illinois, Chicago, Illinois, USA