Researchers in Brazil have identified the first evidence of vertical transmission of the Oropouche virus, meaning from mother to child during pregnancy.
This finding, published in the New England Journal of Medicine (NEJM), represents a significant advance in the understanding of the disease, classified by the World Health Organization (WHO) as having a “high regional risk” in the Americas due to its rapid spread.
Traditionally, the Oropouche fever virus has been transmitted through the bite of Culicoides paraensis, commonly known as "jejen," as well as certain varieties of mosquitoes.
However, the confirmed case of vertical transmission highlights new risks, particularly for pregnant women in areas where the virus is endemic.
The study focused on a 40-year-old Brazilian woman, who was 30 weeks pregnant, and presented with fever, muscle aches, and headaches; she eventually experienced dark vaginal bleeding, after which doctors confirmed the fetal demise.
After weeks of symptoms and complications during the pregnancy, molecular tests confirmed the infection by Oropouche, ruling out other viruses such as dengue, zika, and chikungunya. The virus's RNA was detected in fetal tissues, linking the infection to fetal death.
The phylogenetic analysis revealed that the virus belonged to emerging strains from the current outbreak in Brazil, underscoring the risks associated with this new mode of transmission.
Since its description in 1955, the virus has caused sporadic outbreaks in South America and the Caribbean. In 2024, Oropouche fever spread to previously disease-free regions in Brazil, driven by emerging genetic variants.
Experts warn that this expansion could reach other countries in the region, such as Argentina, where the vector is present.
In Cuba, the disease began to spread last year and is now present throughout the island.
The Pan American Health Organization (PAHO) recommends actions such as eliminating water sources where insects breed; using nets, repellents, and mosquito nets to prevent bites; and strengthening epidemiological surveillance in endemic areas.
Recent research in Italy detected RNA from the Oropouche virus in the semen of a patient, suggesting the possibility of sexual transmission.
Although more studies are needed, this could represent another previously undocumented route of transmission.
With these new findings, experts emphasize the need to raise awareness about Oropouche fever, especially among pregnant women and travelers to affected regions.
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