Supported by the China-U.S.Collaborative Program on Emerging and Re-emerging Infectious Diseases(No.1U2GGH000018-01);the National Basic Research Program of China(973Program)(No.2010CB530206);the National Science and Technology Key Project on Major Infectious Disease(Nos.2008ZX10004-002,2008ZX10004-008,2009ZX10004-203,2012ZX10004-215)~~