Genomic characterization, origin, and local transmission of Oropouche virus in Bolivia in 2024.

Background: The Oropouche virus (OROV) is an arthropod-borne virus that causes an acute febrile illness, like other arboviral diseases. In 2024, Oropouche cases sharply increased in several countries of the Americas, including Bolivia. Here, we investigate the origin and spread of OROV in the Bolivian Amazon region. Methods: Full-length OROV genomes from 34 positive samples collected in the three affected Bolivian departments during the 2024 outbreak were sequenced using an amplicon-based approach. Maximum Likelihood (ML) phylogenetic analyses of separate viral segments were conducted to identify the responsible viral lineage. Bayesian phylogeographic analysis of concatenated viral segments was used to reconstruct the viral spatiotemporal dispersion pattern within the country. Findings: The first Oropouche cases in Bolivia 2024 were reported using samples collected from the Pando department during mid-January, and the peak of Oropouche cases occurred in mid-April. The phylogenetic analysis of OROV genomes revealed that all cases detected in Bolivia belong to the novel reassortant OROV clade that drove the recent epidemic in Brazil. Our phylogeographic analysis detected at least two exportation events from the Brazilian state of Acre to the Bolivian municipalities of Guayaramerín and Riberalta, both located in the Beni department, with subsequent dissemination to municipalities of Pando and La Paz departments. Viral introductions likely occurred between early October and early November 2023, indicating a lag of approximately three months between the introduction of OROV and its detection. Interpretation: Our findings confirm that OROV spread at least twice from the western Brazilian Amazon to the neighboring Bolivian department of Beni in late 2023, successfully establishing regional transmission chains. These findings underscore the critical need for active OROV surveillance across the border Amazonian region between Brazil and Bolivia. They also confirm the potential for sustained OROV transmission within the Bolivian Amazon, highlighting the importance of preparedness for future outbreaks. Funding: This publication was in part supported by the Cooperative Agreement Number NU50CK000639 awarded to the Pan American Health Organization and funded by the Centers for Disease Control and Prevention.