A study on Oropouche virus (OROV) has shed light on recent and historical outbreaks of this neglected virus in Latin America and the Caribbean. The study was performed in collaboration with Euroimmun and Euroimmun Brazil and was published in Nature Medicine.
Background to Oropouche virus
OROV is an arbovirus that causes the febrile illness Oropouche fever. Although often mild and self-limited, OROV infection in some patients can lead to serious complications such as meningitis, encephalitis, adverse pregnancy outcomes and death. The virus is primarily transmitted to humans via Culicoides paraensis midges.
OROV has been endemic in the Amazon region since the 1950s. In late 2023, it re-emerged causing a major epidemic across Central and South America. This re-emergence is associated with a novel OROV reassortment that may have higher fitness and virulence. Factors such as land use, land cover and human mobility likely facilitated OROV re-emergence. Furthermore, infected travellers, the widespread distribution of the C. paraensis vector and an immunologically naïve population may have contributed to its spread beyond the Amazon region.
Seroprevalence in a metropolitan hub
The study investigated the transmission dynamics of OROV in Manaus City, Brazil – the largest metropolis in the Amazon region. The city has a high population density and substantial human mobility facilitated by a large airport, making it a potential hub for OROV dissemination beyond the Amazon region. The reported cumulative incidence of Oropouche fever is higher in Manaus than at the national level.
OROV seroprevalences were investigated in blood donor samples at distinct time points using the Euroimmun Anti-Oropouche Virus ELISA (IgG)/(IgM)*. The data show that OROV re-emergence resulted in an increase in IgG seroprevalence from 11.4% in November 2023 to 25.7% in November 2024. A high agreement between the ELISA and a focus reduction neutralisation test confirmed the robustness of the results. Neutralisation studies revealed that OROV-specific IgG antibodies from previously infected individuals could neutralise both the historical and the contemporary strain.
Transmission dynamics
Reconstruction of historical OROV circulation in Manaus indicates a continuous low-level of OROV transmission, with major outbreaks occurring in 1980-1981 and in 2023-2024. The two outbreaks shared a comparable seasonality and magnitude. Using a compilation of outbreak and seroepidemiologic data from 1960 to 2022, the number of infections across Latin America and the Caribbean during this time was estimated to be more than 9.4 million. The gap between recorded cases and the estimated number of infections suggests a historical underreporting of OROV infections.
Why this study is important
The study provides a comprehensive assessment of OROV transmission in Manaus, contributing to a better understanding of the dynamics and drivers of OROV spread and the burden of the virus in Latin America and the Caribbean. The likely underdetection of OROV reinforces the importance of continuous surveillance and qualified diagnostics in regions with multiple circulating arboviruses.
*The Anti-Oropouche Virus ELISA (IgM) and Anti-Oropouche Virus ELISA (IgG) are authorised by ANVISA in Brazil and will soon also be available with CE marking.
Find the study here:
Manuli, E.R., Hua, X., Scachetti, G.C. et al. Transmission dynamics of Oropouche virus in Latin America and the Caribbean. Nat Med 32, 1383–1392 (2026). https://doi.org/10.1038/s41591-026-04221-z.
