WZJ and HBY equally conceived and designed the research plan, and performed the majority of the study and analyzed the data, and contributed to drafting of the manuscript. AJG, YCW, FZ and SHZ performed part of the study, and provided technical assistance. WGS and FBQ conducted the related animal infection experiments. XQZ and HTC contributed to partial analysis of the data and the revision of the manuscript. DTJL took the lead on analysis of the data and drafting of the manuscript. XPC participated in all aspects of the study, supervised the research and provided funds. All authors read and approved the final manuscript.