Arbovirus transmission involves an interplay between host, virus, and environmental factors. Because of the complexity of interactions, the transmission success of arboviruses could either be a function of viral fitness or be stochastic. In the present study, using 1,963 envelope (E) gene sequences and 239 whole genomes, we conducted a large-scale molecular epidemiological analysis of a dengue virus type 1 (DENV-1) population to understand the transmission success, evolution, and dispersal patterns of different lineages of DENV-1 circulating in Singapore from 2011 to 2016. The study population was highly dynamic and heterogeneous. However, only a handful of genetically distinct strains (n = 6) established sustained transmission, but at variable levels of dominance. Phylogeographic analysis revealed a weak spatial clustering and 35 well-supported diffusion pathways, implying widespread and complex dispersal of these strains in local settings. Yet, the dominant strains were neither evolving faster than less dominant ones nor under positive selection. These observations suggested that lineage dominance was likely to be stochastic and opportunistically driven by non-viral factors such as host immune pressure and vector abundance. Our findings, therefore, emphasize the implications of understanding the vector and human factors in parallel to virus dynamics on continuing efforts to control the arbovirus disease transmission in endemic regions.
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