Abstract
In August 2013, Xishuangbanna, Yunnan Province, China, had its first dengue outbreak. Dengue virus (DENV) RNA detection in sera or viral isolates revealed that all 222 autochthonous patients detected and three Chinese travelers from Laos (imported cases) were positive for DENV-3 serotype, while DENV-1 and DENV-4 were detected in travelers from Myanmar and Thailand during the outbreak. For 33 suspected dengue cases collected before the outbreak, two imported cases from Laos and nine residents living in Laos (Laotian cases) were positive for DENV-3. Further, a random subset of 33 positive cases for DENV-3 was sequenced for the full envelope gene of DENV. Phylogenetic analysis showed that all of the 25 autochthonous cases sequenced were grouped into the same clade, genotype II of DENV-3, with imported cases from Laos and Laotian cases. These results suggest that the genotype II of DENV-3 was associated with the outbreak and may have originated from the virus circulating in Laos.