广东省科技计划项目2013B060400012,2014A020219004;中美新发和再发传染病合作项目1U2GGH000018-01Science and Technology Planning Project of Guangdong Province of China2013B060400012, 2014A020219004;US-China Cooperation Program on Emerging and Reemerging In-fectious Diseases1U2GGH000018-01