New mega RNA virus discovered in Pacific oysters during mass die-offs
Scientists have discovered a new mega RNA virus in farmed Pacific oysters during a mass die-off in British Columbia (B.C.), Canada. The finding, published in the Proceedings of the National Academy of Sciences (PNAS), could explain recurring oyster mortality events and highlights the urgent need for stronger biosecurity measures in aquaculture.
Pacific oysters, valued at $16 million in British Columbia in 2023, are the world’s most widely farmed shellfish. Yet in recent years, growers have witnessed unexplained mass die-offs. While bacteria, warming waters, and other viruses have been implicated, in many cases, the cause has remained uncertain.
The discovery of Pacific Oyster Nidovirus 1
Researchers collected oysters from farms and wild populations during a 2020 die-off. Using RNA analysis, they identified a previously unknown virus, now named Pacific Oyster Nidovirus 1 (PONV1), in 20 dead and dying oysters from farms. Notably, the virus was absent in healthy wild oysters, pointing to a potential link between PONV1 and oyster mortality.
“This discovery highlights how little we know about viruses infecting invertebrates in general and oysters in particular,” said Dr. Curtis Suttle, senior author and professor at the University of British Columbia (UBC). “Prevention is not possible until the causes are known.”
Genomic insights and global spread
The newly identified virus has one of the largest RNA genomes ever recorded and is only the second nidovirus detected in bivalves. Nidoviruses are found across many species, including humans, where SARS-CoV-2 causes COVID-19.
Dr. Kevin Zhong, lead author and research associate at UBC, explained that the large genome could allow the virus to encode more genes or protein domains, potentially expanding its ability to infect hosts.
Global databases revealed 15 related viruses in oysters in Europe and Asia, suggesting the pathogen may already be widespread. The research team has proposed a new virus family: Megarnaviridae, or “large RNA viruses.”
No risk to humans but caution for aquaculture
Experts stress that PONV1 appears to be oyster-specific and poses no risk to human health. However, the findings raise concerns about the movement of oyster seed and spat between hatcheries and farms.
“Oyster growers should use an abundance of caution when moving spat internationally and domestically,” Dr. Suttle said. “Developing rapid tests for detecting pathogens is essential for safe aquaculture and protecting oyster populations.”
Protecting the future of shellfish farming
The researchers emphasize that while the discovery is not cause for alarm, it is a crucial step toward safeguarding sustainable shellfish aquaculture. Continued monitoring and genetic analysis will help identify the role of PONV1 in mass oyster die-offs and protect the industry from future losses.
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