A new study estimates that over 9.4 million people in Latin America and the Caribbean were infected with Oropouche virus between 1960 and 2025 – a figure significantly higher than officially reported case numbers. Understanding the true scope of this arbovirus is crucial for public health preparedness and resource allocation in affected regions.
Published on Tuesday, March 24, 2026, in Nature Medicine, the research – a collaboration between the University of São Paulo’s Faculty of Medicine (FMUSP), the University of Kentucky, the State University of Campinas (Unicamp) and the Amazonas State Foundation for Hematology and Hemotherapy (Hemoam) – reveals a substantial discrepancy between estimated infections and diagnosed cases. In Manaus, Brazil, a recent epicenter of transmission, the total number of infections may be up to 200 times greater than confirmed cases.
Oropouche fever, transmitted by midges (Culicoides paraensis), causes symptoms similar to dengue, but can lead to severe complications, including neurological issues, maternal-fetal problems, and even death. Currently, there are no available vaccines or specific antiviral treatments.
The gap between estimated and reported infections is largely due to underdiagnosis of the disease. Limited access to healthcare in remote areas of the Amazon, where travel to medical facilities can capture over 24 hours, contributes to many cases going undiagnosed. A significant proportion of infections are asymptomatic or present with mild symptoms.
“Only a slight proportion of infected people develop the disease, which widens the difference between the number of infections and registered cases,” says Erika Manuli, a researcher at FMUSP.
Manaus as a Recent Epicenter and Outbreak Pattern
The data indicates that Manaus played a central role in the recent expansion of the virus. Between late 2023 and mid-2024, the proportion of people with antibodies against Oropouche more than doubled, increasing from 11.4% to 25.7% based on analyses of blood donors.
The Amazonian capital has likewise experienced two major outbreaks, spaced 42 years apart – in 1980–1981 and 2023–2024 – both peaking during the rainy season and affecting more than 12% of the population.
The study also points to factors like high population density and air travel as contributors to the spread of Oropouche to new areas, including all Brazilian states, as well as countries in the Caribbean, and cases linked to travel to Europe and North America.
Distinct Dynamics Compared to Dengue, Zika, and Chikungunya
A second study from the same group, published simultaneously in Nature Health, demonstrates that Oropouche exhibits a different pattern compared to other arboviruses.
While diseases like dengue, chikungunya, and Zika are associated with urban environments and the Aedes aegypti mosquito, Oropouche primarily occurs in rural areas and regions near forests, where midges – which require high humidity environments – are more prevalent.
Study Calls for Re-evaluation of Control Strategies
The findings suggest that current vector control strategies, primarily focused on urban mosquitoes, are insufficient to contain the spread of the virus. The research underscores the need for a more comprehensive approach to address this emerging public health threat.
“Monitoring the presence of antibodies in the population is essential to understand the dynamics of transmission and guide public health strategies, including the development of vaccines,” says Prof. Dra. Ester Sabino, a professor at FMUSP’s Department of Pathology.
Funding
The study received support from Wellcome Trust, National Institutes of Health (NIH), the São Paulo Research Foundation (FAPESP), the Brazilian Ministry of Science, Euroimmun, and Todos pela Saúde Institute.
