1. Department of Infectious Diseases and Microbiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.
2. Department of Molecular Genetics and Biochemistry, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.
3. Department of Pathogenic Molecular Biology, Beijing Institute of Microbiology and Epidemiology, Beijing, China.
4. Department of Infectious Diseases, Capital University of Medical Science Youan Hospital, Beijing, China.