[Article published on January 24, 2026]
Beneath the surface of the oceans, a discreet biodiversity still largely escapes the radar of science. While large marine mammals fascinate with their size and intelligence, their microbial world remains largely unexplored. A recent study conducted on orcas and dolphins suggests that these animals have long been hosting unknown viruses, carrying valuable clues about the evolutionary history of the oceans.
A virological discovery expanding the map of marine life
By analyzing tissues sampled from short-finned pilot whales in the Caribbean, an international team of researchers identified two previously undescribed viruses. These infectious agents belong to the circovirus family, a group of DNA viruses known in many land animals but rarely observed in marine species. Five complete genomes were detected in short-finned pilot whales and two in orcas, all from the North Atlantic.
This discovery, published in the journal Virology under the guidance of virologist Arvind Varsani, marks a regional first. No circovirus had been detected in cetaceans in this area of the globe before. It is based on high-throughput sequencing, a method capable of extracting very precise genetic data. These analyses sometimes rely on samples stored for several years.
The viruses of cetaceans could have been part of their lineage for millions of years
Beyond their simple identification, these viruses intrigue with their genetic uniqueness. Researchers have demonstrated that their genomes differ significantly from those of other known circoviruses, with less than 65% overall similarity. Such divergence suggests an ancient history, possibly related to the evolution of the cetaceans themselves.
Analysis of the capsid protein, which forms the outer envelope of the virus, strengthens this hypothesis. Certain regions exposed on the surface appear unusually developed, including a loop involved in immune system recognition. This type of adaptation resembles mechanisms observed in circoviruses infecting terrestrial mammals like pigs, hinting at similar immune pressures despite very different environments.
These clues lead the authors to consider an ancient coevolution between these viruses and the ancestors of current cetaceans. However, they carefully formulate this hypothesis, as it still requires confirmation through the analysis of a larger number of species and oceanic regions.
What this discovery changes in the understanding of oceanic ecosystems
The discovery of these viruses does not imply that the affected orcas or dolphins were sick. At this stage, researchers have not established any direct link to a pathology. In other animals, some circoviruses can cause immune disorders, but their presence does not necessarily lead to an observable disease. This nuance is essential to avoid any alarmist interpretation.
However, these results highlight how imperfectly known marine ecosystems are, even among emblematic species. They also emphasize the importance of biological collections and local collaborations, particularly with communities engaged in regulated subsistence hunting, without which this data would remain inaccessible.
Revealing the existence of viruses in previously invisible cetaceans, this study highlighted by SciTechDaily opens a new path to explore the role of the viral world in the balance of the oceans. It suggests that, beyond visible threats, an essential part of marine life plays out on a microscopic scale, where science and exploration are only just beginning.
