Infection with the Oropouche virus (or OROV infection) is one of the leading causes of arbovirus disease in South America after dengue fever, with 2 to 5 million people directly affected. Since 2023 and 2024, this virus has expanded its range of circulation due to changes in the environment and biodiversity, demographic shifts, and human mobility.

The significance and scope of this threat contrast with the fragmented or imprecise knowledge regarding the transmission cycle, vectors, and their ecology in these regions.

This is why it was important for Santé publique France and its partners to publish an initial risk analysis conducted in December 2024, in order to assess the potential health risks in French Guiana and the French Antilles.

Three questions for Jean-Claude Désenclos, co-author of this initial risk assessment

What is Oropouche virus infection?

The “Oropouche” disease is caused by an arbovirus, the Oropouche virus or OROV. OROV belongs to the Orthobunyavirus genus, whose RNA is segmented (like that of the influenza virus), allowing it to reassort and generate new emerging viral strains.

OROV infection affects both animals and humans:

• in forests, within a sylvatic cycle, via transmission by arthropods;

• and in peri-urban/urban areas through human-to-human transmission via anthropophilic midges, primarily Culicoides paraensis (other vectors are under discussion, including Culex quinquefasciatus).

The host and vector species that maintain the sylvatic cycle of OROV are still poorly understood.

The disease in humans is characterized by acute flu-like symptoms (fever, headache, joint and muscle pain, etc.) that resolve spontaneously within a few days. Neurological complications (aseptic meningitis) may, however, occur. Diagnosis relies on a blood test (RT-PCR on a sample taken within the first 7 days of illness or via serology).

In the absence of these tests in clinical practice, the disease goes unrecognized, and its symptoms do not allow for distinguishing OROV infection from other arboviral diseases. Consequently, its prevalence is greatly underestimated, and outbreaks go undetected. There is no specific treatment or vaccine against OROV infection, and treatment is symptomatic.

Why did Santé publique France and its partners conduct a risk assessment?

A risk analysis allows for the early assessment of emerging threats, whether they are infectious in nature, environmental, or related to risky behaviors. By assessing the likelihood and impact of these risks, health authorities can prioritize the actions to be taken and implement appropriate preventive or corrective measures.

Furthermore, the years 2023 and especially 2024 saw an epidemic resurgence of OROV infection in South America (Brazil, Peru, Colombia, Bolivia, Guyana, and then, in 2025, Venezuela) that was significantly greater than in previous years. This resurgence was accompanied by an expansion of transmission zones into Panama and the Caribbean (Cuba, Barbados). Multiple cases were also imported via travelers to North America and Europe.

This epidemic wave is caused by a new sublineage of the Oropouche virus, resulting from the reassortment of several OROVs. Studies conducted during the 2023–2024 epidemic resurgence showed that this sublineage was first detected during the 2020 epidemic in a village in a forested area of the interior of French Guiana. It is believed to have a greater capacity for replication (and potentially for transmission and spread) and may more easily evade the protection conferred by immunity acquired from past infections. Furthermore, these studies indicate that the expansion of the virus’s transmission area is linked to changes in the environment and biodiversity, as well as demographic shifts and human mobility.

For the first time during the 2024 epidemics, severe cases resulting in death and cases of mother-to-fetus transmission with congenital malformations were reported. Similarly, Guillain-Barré syndrome was observed in Cuba, and possible sexual and blood transfusion transmission were identified.

This situation led Santé publique France to hypothesize that the establishment of virus transmission cycles in the French departments of the Americas (DFAs) was becoming possible, even probable. A multidisciplinary risk analysis was conducted by Santé publique France and its partners to prepare a response to this new epidemic threat.

What is the risk of this disease in the Caribbean and French Guiana?

The marked shift in the epidemiology of OROV infection in South America and the Caribbean in 2023 and 2024 led us to significantly raise, in August 2024, the risk for French Guiana and the French West Indies compared to the 2020 epidemic. The analysis report concluded in 2024 that there was a high risk of an epidemic in French Guiana, Martinique, and Guadeloupe (with high uncertainty in French Guiana and Guadeloupe and low uncertainty in Martinique).

However, significant uncertainties remain, reflecting the currently fragmented scientific data regarding viruses, hosts, and vectors, as well as their interactions.

This is why the risks estimated in August and December 2024 are likely to change. They are highly dependent on the epidemiological situation in the territories with which exchanges take place, requiring regularly updated international monitoring.

Santé publique France emphasizes the need to prepare the affected territories, in particular by:

• Strengthening the healthcare system by enhancing diagnostic capabilities

• Improving surveillance and early warning systems

• Developing mosquito control measures

• Continuing epidemiological and entomological investigations

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