Co-Circulation of 3 Dengue Virus Serotypes led to a Severe dengue outbreak in Xishuangbanna, a border area of China, Myanmar and Laos, 2019.

Dengue fever has been included in the top ten global health threats announced by the World Health Organization (WHO) in early 2019. In some southern provinces of China, autochthonous outbreak have also been reported in the last decade. An unexpected large outbreak of dengue fever was reported in Xishuangbanna, a border area of China, Myanmar and Laos, in 2019. Among the 226 hospitalized cases, 90 were diagnosed with severe dengue according to the 2009 World Health Organization guidelines. Serotyping and Phylogenetic analyses of envelope gene sequences from 246 randomly selected samples showed that 3 serotypes dengue viruses co-circulating in this outbreak, which is very rare in this area. Dengue virus serotype 1 (DENV-1, genotype I) and serotype 2 (DENV-2, Cosmopolitan genotype and Asian genotype) were the main pathogenic agent of this outbreak. The Dengue virus serotype 3 (DENV-3) epidemic strains were classified as genotype Ⅲ, which was close to Thailand 2015 epidemic strain. The co-circulation may lead to more serious clinical symptoms and larger epidemic scale. This finding is of great importance to understand the circulation of DENV and strengthen the detection and management of dengue fever in border areas.