Molecular epidemiological characteristics of dengue virus serotype 3 in Yunnan Province, China, 2014–2020: A cross-sectional study

Background Dengue fever, caused by dengue virus serotype 3, has represented a significant public health challenge in Yunnan Province, China, for nearly a decade. The frequent movement of individuals across neighboring countries continuously threatens local outbreaks. Nevertheless, there remains a considerable gap in research regarding the genetic evolution and migration pathways of DENV-3. Methods This study collected 161 DENV-3 E gene sequences from patients with indigenous and imported dengue fever from Myanmar in Yunnan Province between 2014 and 2020. The maximum likelihood method was employed to construct a phylogenetic tree for identifying genotype subtypes. Additionally, the Bayesian phylogeographic reconstruction method was utilized to infer the spatial migration patterns and ancestral geographic origins of the virus. A molecular transmission network was also established based on genetic distances between sequences to identify and characterize high-risk transmission clusters. Results The phylogenetic analysis indicated the presence of a co-circulating epidemic of genotype I and genotype III in Yunnan. The Bayesian skyline plot demonstrated that the effective virus population size of DENV-3 underwent significant expansion from 2016 to 2018. Phylogeographic analysis identified Myanmar and Laos as the primary source hubs for DENV-3 transmission in Yunnan (Bayes factor >100). The molecular transmission network revealed four major high-risk transmission clusters, highlighting the mutual transmission of DENV-3 among Yunnan, Myanmar, and Laos. Conclusion The frequent cross-border movement of individuals is the principal driver of DENV-3 importation into Yunnan and the maintenance of local circulation. Enhanced surveillance of dengue virus genotypes and importation pathways within the cross-border human is essential for mitigating dengue virus transmission.