by Justin Jackson , Medical Xpress

Credit: Pixabay/CC0 Public Domain

The first confirmed case of vertical transmission of Oropouche virus (OROV) has been reported by 23 researchers from eight distinct institutions in Brazil.

OROV, a zoonotic arbovirus, was first isolated from the blood of a charcoal worker with a high fever in 1955 on the Caribbean island of Trinidad. Outbreaks have typically occurred south of the Amazon, isolated within Amazonian villages.

In 2024, OROV infections were detected in previously non-endemic areas across all five Brazilian regions. These expansions into previously unaffected regions involve new virus variants emerging from genetic reassortment.

In a letter to the editor titled "A Case of Vertical Transmission of Oropouche Virus in Brazil," published October 30, 2024, in the New England Journal of Medicine, researchers report on a case from Ceará, a state historically free from OROV, finding its first infection case through active laboratory surveillance.

Subsequent investigations identified 171 cases, predominantly in the rural valleys of the Baturité Massif. Agricultural landscapes in this region favor the Culicoides paraensis midge, a small biting fly sometimes referred to as "no-see-ums" due to their tiny size. Culicoides is the primary vector for OROV transmission to humans.

A notable case involved a 40-year-old pregnant woman at 30 weeks gestation who developed fever, chills, muscle aches, and severe headache. Routine prenatal care had previously identified gestational diabetes, managed with metformin, and four routine obstetric ultrasounds.

On July 27, medical evaluation revealed light vaginal bleeding and dark discharge, with ultrasonography indicating fetal macrosomia.

By August 5, continued symptoms and decreased fetal movements led to the confirmation of fetal demise.

Molecular diagnostics confirmed acute OROV infection, ruling out dengue, Zika, chikungunya, and Mayaro viruses. Minimal invasive tissue sampling of the stillborn infant revealed OROV RNA in multiple fetal tissues, establishing vertical transmission.

Phylogenetic analysis using maximum-likelihood inference positioned the virus within the OROVBR-2019-2024 lineage, consistent with strains from the ongoing outbreak. These findings link the stillbirth directly to the current OROV spread in Brazil, highlighting the virus's potential risks during pregnancy.

The report should sound the alarm for health care providers to consider OROV infection in pregnant women presenting with fever and related symptoms in endemic or emerging regions.

More information: Carlos Garcia Filho et al, A Case of Vertical Transmission of Oropouche Virus in Brazil, New England Journal of Medicine (2024). DOI: 10.1056/NEJMc2412812

Journal information: New England Journal of Medicine 

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