23 researchers from 8 different institutions in Brazil have reported the first confirmed case of vertical transmission of Oropouche virus (OROV). OROV is a segmented, single-stranded RNA virus classified under the family Peribunyaviridae and the genus Orthobunyavirus. It was first discovered in 1955 in Vega de Oropouche, Trinidad and Tobago. Typically, outbreaks have occurred south of the Amazon, locked to Amazonian villages.
In the five Brazilian regions, OROV infections were detected in previously non-endemic areas in 2024. New virus variants emerge through genetic reassortment, and these expansions into previously unaffected regions. In the October 30, 2024, issue of the New England Journal of Medicine, researchers report a case of vertical transmission of the Oropouche Virus in Brazil, a case in Ceará, a state historically free of OROV, which is the first OROV infection case found through active laboratory surveillance.
A total of 171 cases were subsequently identified in the rural valleys of the Baturité Massif. The large, biting fly in this zone, also known as ‘no see ums,’ is the agricultural landscape’s preference, the Culicoides paraensis midge. The primary vector of OROV transmission to humans is Culicoides.
One of the most visible cases involved a 40-year-old pregnant woman at 30 weeks gestation who became ill (fever, chills, muscle aches, severe headache). During routine prenatal care, she was diagnosed with gestational diabetes, which was managed with metformin, four obstetric ultrasounds were conducted as part of her care.
On July 27, the patient presented with light vaginal bleeding and dark discharge; she also developed fetal macrosomia by ultrasonography. The fetal demise was confirmed by continued symptoms and decreased fetal movement by August 5. Acute OROV infection was confirmed by molecular diagnostics and excluded dengue, zika, chikungunya, and mayaro viruses. Vertical transmission of OROV RNA was established by minimal invasive tissue sampling of the stillborn infant which demonstrated OROV RNA in multiple fetal tissues.
Maximum-likelihood inference using phylogenetic analysis placed the virus within the OROVBR-2019-2024 lineage, as seen in strains from the currently ongoing outbreak. These findings directly link the current OROV spread in Brazil to stillbirth, and this indicates that the virus poses risks during pregnancy, the authors said. In health care providers, the report should sound the alarm for OROV infection in pregnant women who present with fever and related symptoms in endemic and emerging regions.
Reference: Garcia Filho C, Lima Neto AS, Maia AMPC, et al. A case of vertical transmission of Oropouche virus in Brazil. N Engl J Med. 2024;391:2055-2057. doi:10.1056/NEJMc2412812
