Dynamics and ecology of a multistage expansion of Oropouche virus in Brazil

In March 2024, Brazil reported an unprecedented Oropouche fever outbreak, driven by the emergence of a reassortant lineage of the Oropouche virus (OROV) expanding beyond the Amazon Basin. To investigate the expansion dynamics of OROV, we implemented complementary phylogeographic and ecological niche modelling approaches that aimed to characterize the environmental factors associated with the range expansion and the risk of local circulation, respectively. Our analyses reveal a multiscale expansion process with both short- and long-distance dispersal events and diffusion velocities in line with air traffic-mediated jumps. We identify banana and cocoa cultivation, temperature, the predicted suitability of the primary vector Culicoides paraensis and human population density as key environmental factors associated with OROV range expansion in new areas. We further show that OROV circulated in areas of enhanced ecological suitability immediately preceding its explosive epidemic expansion in the Amazon. Our study provides valuable insights into the dispersal and ecological dynamics of OROV, highlighting the probable role of human mobility in the long-distance colonization of new areas and raising concern over high viral suitability along the Brazilian coast.