1. Center for Endemic Disease Control, Chinese Center for Disease Control and Prevention, Harbin Medical University, Harbin, China
2. Key Lab of Etiology and Epidemiology, Education Bureau of Heilongjiang Province, Ministry of Health of P. R. China, Harbin Medical University, Harbin, China
3. Department of Pathology, Hospital of Guizhou Medical University, Guiyang, China
4. Key Laboratory of Endemic and Ethnic Diseases of the Ministry of Education of P. R. China, Guizhou Medical University, Guiyang, China