Molecular Characterization and Viral Origin of the 2015 Dengue Outbreak in Xishuangbanna, Yunnan, China

A total of 1067 serum samples were collected from febrile patients in Xishuangbanna, Yunnan, 2015. Of these, 852 cases were confirmed to be dengue NS1-positive. 76 structural protein genes were sequenced through RT-PCR based on the viral RNAs extracted from serum samples. Phylogenetic analysis revealed that all strains were classified as cosmopolitan genotype of DENV-2. After comparing with the DENV-2SS, 173 base substitutions were found in 76 sequences, resulting in 43 nonsynonymous mutations, of which 22 mutations existed among all samples. According to secondary structure prediction, 8 new possible nucelotide/protein binding sites were found and another 4 sites were lost among the 775 amino acids of DENV structural proteins as compared with DENV-2SS. Meanwhile, 6 distinct amino acid changes were found in the helix and strand regions, and the distribution of the exposed and buried regions was slightly altered. The results indicated that the epidemic dengue strains of Xishuangbanna in 2015 are most similar to the Indian strain in 2001 and the Sri Lankan strain in 2004. Moreover, it also show a very strong similarity to the epidemic strains of Fujian province in 1999 and 2010, which show that there is an internal recycling epidemic trend of DENV in China.