Origin, evolution and transmission dynamics of Orthobunyavirus Oropoucheense

Oropouche virus (OROV) is a high-risk emerging arbovirus that causes recurrent febrile outbreaks across tropical Central and South America, posing persistent public health threats with expanding endemic ranges and rising zoonotic spillover risks. Limited comprehensive evidence regarding its genomic plasticity and multi-scale evolutionary dynamics hinders precise epidemic prevention. Herein, we performed systematic phylogenomic analyses of all available OROV sequences to elucidate its recombination profiles, adaptive evolution, cross-species transmission and spatial dispersal patterns. Phylogenetic reconstruction based on breakpoint-free regions revealed two major polyphyletic lineages characterized by extensive multi-host and transboundary circulation, with Brazilian strains dominating global OROV populations. Bayesian ancestral inference identified humans as the likely earliest detectable ancestral host, while all statistically robust host-switching events were closely associated with Callithrix spp., confirming their critical role as intermediate amplifying hosts. Phylogeographic analyses suggested Brazil and Peru as the primary ancestral origins, with neighbouring short-distance diffusion and frequent cross-border transmission forming a multi-path dissemination system concentrated in the Amazon Basin and southeastern coastal zone of Brazil. Pronounced topological incongruence among L, M and N genes demonstrated pervasive segmental reassortment, which has intensified temporally since 2010, especially during 2020-2024. Notably, the M gene undergoes intensive intra-segment recombination and prominent positive selection with relaxed functional constraints, representing the key adaptive hotspot, whereas L and N genes remain highly conserved under strong purifying selection. This study clarifies the synergistic evolutionary mechanisms of recombination, reassortment, host switching and differential selection, providing robust theoretical support for OROV surveillance and targeted intervention.