Dr. Kevin Zhong, a postdoctoral research associate at the UBC Earth, Ocean and Atmospheric Sciences (EOAS) department, has found the Holy Grail. This breakthrough is a big step toward explaining today’s mysterious and persistent mass die-offs of Pacific oysters. This study reveals the existence of a new Mega RNA virus. We suggest calling it Megarnavirus gigas, and it possesses one of the largest RNA genomes ever observed. These recent findings are alarming—perhaps a harbinger of health in an already imperiled oyster population. Beyond these particular cases, their work sheds light on broader implications for shellfish aquaculture.
The study emerges from the collection of 33 oysters from two farms in British Columbia during a mass die-off event in 2020, along with 26 wild oysters sourced from ten nearby sites. In a separate study, researchers found that Megarnavirus gigas (PONV1), another virus, is specific to oysters. This result underscores the potential threat that this virus can pose to marine bivalves. This is just the second nidovirus discovered in bivalves. This finding indicates it may be having a much larger ecological effect than we realized.
A Deeper Look at the Virus
The newly discovered Megarnavirus gigas is remarkable mainly for its size. It has severe secondary consequences for the health of these iconic oysters as well. With its abnormally humongous genome, the virus flips public understanding of RNA viruses and what they can do on its head.
Dr. Zhong commented on the significance of the discovery, stating, “The extraordinarily large genome of this virus makes it particularly fascinating as it pushes the known boundaries of how big RNA virus genomes can get.”
The finding shows an urgent need for more studies. We need to investigate how Megarnavirus gigas is linked to increased mortality in Pacific oysters. Dr. Curtis Suttle, EOAS professor and senior author of the study, said that grasping these dynamics is essential. “It’s important to investigate mass die-offs in oysters to determine what causes disease,” he noted. “Similar to humans, disease and death is not caused by a single factor, but prevention is not possible until the causes are known.”
Global Context and Implications
The other 15 closely related viruses were found in Pacific oysters from representing Europe and Asia. Through global genetic databases, these viruses were made known. This conclusion further demonstrates that Megarnavirus gigas (PONV1) and its relatives are present worldwide. The widespread presence of this pathogen raises serious concerns for the health of oyster populations around the world.
Dr. Zhong pointed out that there have been annual mass die-offs in British Columbia and beyond, stating, “We’ve recently seen annual mass die-offs in B.C. and elsewhere of Pacific oysters, the most widely farmed shellfish worldwide.” He continued, “A lot of times, we don’t know why.
Considering these recent events, Dr. Suttle recommended that growers be extra careful when transporting oyster spat both internationally and domestically. He cautioned that during these transfers is when new pathogens are likely to be generated. He stressed the need to be able to develop rapid tests when these threats are detected.
The Economic Impact on Shellfish Aquaculture
Pacific oysters play an important role in British Columbia’s shellfish industry, worth an estimated $16 million in 2023. Virus- and bacteria-induced mass die-offs exacerbated by increasing water temperatures take an enormous toll on this burgeoning economic sector. The results from this study highlight the need for continued evaluation of oyster populations to protect this crucial natural resource.
In response to alarmed stakeholders, Dr. Suttle eased fears by saying, > “This research should not be of concern. Perhaps most importantly though, he shared with me, was the excitement about how fundamental of a study this will be for oyster health. It helps accomplish the long-term sustainability of shellfish aquaculture. He noted, > “This discovery highlights how little we know about viruses infecting invertebrates in general and oysters in particular.”
Researchers are uncovering the secrets of Megarnavirus gigas and its connection to oyster mortality. They emphasize the need for continued research to minimize future risks associated with oyster farming.