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Wednesday, 19 August 2026dailybeirut.com
Health
Two new studies reveal that the Oropouche virus has infected approximately 9.4 million people across Latin America and the Caribbean since 1960, far exceeding reported cases.
Researchers estimate that about 9.4 million individuals in Latin America and the Caribbean have contracted the Oropouche virus since 1960, a figure significantly higher than official reports indicate. Brazil alone may account for around 5.5 million of these infections, according to two studies published in Nature Medicine and Nature Health.
The Oropouche virus, previously little known outside the Amazon region, gained international attention following a large outbreak in Brazil during 2023. This outbreak infected tens of thousands, caused the country’s first confirmed death from the virus, and extended beyond its traditional Amazonian boundaries. The World Health Organization (WHO) has since called for the rapid development of improved surveillance, prevention, and control tools.
In Manaus, the largest city in the Amazon, an estimated 300,000 people were infected between 2023 and 2024, a number nearly 260 times greater than the officially confirmed cases. Antibody prevalence in the population rose from 11.4% in November 2023 to 25.7% in November 2024, indicating widespread transmission.
William de Souza, a professor at the University of Kentucky and co-author of the study, explained that the virus circulated silently before reaching urban outskirts, with many cases being asymptomatic or mild and therefore undiagnosed. Manaus, with over two million residents, serves as a gateway to the Amazon region, contributing to the virus’s spread across Brazilian states and neighboring countries, prompting an international alert from the WHO.
Access to healthcare in remote Amazon areas is limited, often requiring patients to travel over 24 hours to reach medical facilities. This logistical difficulty likely resulted in many undiagnosed cases, allowing the virus to circulate unnoticed until it reached urban centers. The researchers identified two major outbreaks in Manaus, one in the 1980s and another in 2023, each infecting more than 12% of the population.
Long-lasting immunity was observed, as individuals infected in the 1980s could neutralize newer viral strains, suggesting potential for future vaccination strategies.
The 2023 resurgence confirmed the virus’s wide spread across Brazil, with Espírito Santo reporting the highest cumulative incidence at 318 cases per 100,000 people. The Southeast region accounted for 57.9% of reported cases. Unlike other arboviruses transmitted by mosquitoes like Aedes aegypti, the Oropouche virus is spread by the gunpowder midge (Culicoides paraensis), which breeds in moist soil rich in organic matter rather than standing water.
Cases were found to be 11 times more common in rural areas than urban centers. Souza noted that the midge’s habitat in humid, vegetated areas explains the rural predominance of the disease, differing from urban mosquito-borne diseases.
Because the gunpowder midge inhabits forested and vegetated outskirts rather than urban drains, traditional urban mosquito control methods such as fumigation in public squares and streets are unlikely to be effective against Oropouche virus transmission. The midge is approximately three times smaller than a typical mosquito and can pass through many mosquito nets.
Researchers also identified a new viral lineage formed through genetic reassortment, a process where two viruses infect the same cell and exchange genetic material. This reassortment may enhance viral replication and reduce the effectiveness of antibodies from previous infections, potentially facilitating the virus’s expansion into new areas.
José Luiz Proença Módena, coordinator of the Laboratory for the Study of Emerging Viruses at the State University of Campinas and co-author of the studies, emphasized that current surveillance systems underestimate the disease’s true scale due to the midge’s differing behavior compared to Aedes mosquitoes. He advocates for surveillance efforts that extend beyond large urban centers to include remote areas.
The researchers recommend structural changes in monitoring Oropouche virus, including continuous serological studies, utilizing blood banks as early warning systems, and integrating digital and genomic tools to track outbreaks and mutations. They also stress decentralizing laboratory testing and establishing ongoing surveillance combining environmental, serological, and genomic data to anticipate risks and guide vaccination efforts.
The studies, funded by Brazil’s National Council for Scientific and Technological Development (CNPq), the Todos Pela Saúde Institute, the U.S. National Institutes of Health (NIH), and the Wellcome Trust, provide a comprehensive analysis of the virus’s transmission dynamics and ecological drivers in Latin America and the Caribbean.
