Scientists at the University of British Columbia have discovered a previously unknown virus in farmed Pacific oysters during a mass die-off in B.C. in 2020.
The paper, published on Monday in the Proceedings of the National Academy of Sciences, said that while mass die-offs have been attributed to various factors, including viruses, in many cases, there is no definitive cause.
“We’ve recently seen annual mass die-offs in B.C. and elsewhere of Pacific oysters, the most widely farmed shellfish worldwide,” said first author Dr. Kevin Zhong, research associate in the UBC Department of earth, ocean and atmospheric sciences (EOAS).
The researchers collected 33 oysters from two farms in B.C. during a mass die-off in 2020, as well as 26 wild oysters from 10 nearby sites.
RNA analysis revealed the presence of a previously unknown virus, Pacific Oyster Nidovirus 1 (PONV1), in 20 of the dead and dying farmed oysters, according to the research. However, the virus was not found in healthy wild oysters, which suggested the virus was killing the oysters.
“This discovery highlights how little we know about viruses infecting invertebrates in general and oysters in particular,” said senior author Dr. Curtis Suttle, professor of earth, ocean and atmospheric sciences, botany, microbiology and immunology, at the Institute for the Oceans and Fisheries.
The virus, which has one of the largest RNA genomes on record, according to the research, is so genetically different from other nidoviruses that the research team has proposed a new family, Megarnaviridae, or ‘large RNA viruses’ PONV1, which the team is proposing to name Megarnavirus gigas, or ‘large RNA virus giant.’
Suttle said these large RNA viruses appear to be specific to oysters, so humans are not at risk of contracting the virus.
However, the team said this discovery is a reminder that oyster farmers should use an abundance of caution when moving juvenile oysters as little is known about what causes disease in the bivalve molluscs.
“This research is not a cause for alarm,” Suttle added. “Rather, this is a meaningful step forward in advancing our understanding of oyster health and supporting the long-term sustainability of shellfish aquaculture.”
