1. Key Laboratory of Animal Virology of Ministry of Agriculture, Zhejiang University, Hangzhou, P.R. China.
2. Current address, Research Center of Molecular Medicine of Yunnan Province, Kunming University of Science and Technology, Kunming, P.R. China.
3. State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, The First Affiliated Hospital, Zhejiang University, Hangzhou, P.R. China.