Read the full article via UBC News: New mega RNA virus may hold the key to mass oyster die-offs.

Scientists have identified a previously undocumented virus, Pacific Oyster Nidovirus 1 (PONV1), associated with farmed Pacific oysters during a mass die-off in B.C., Canada. This finding, published in Proceedings of the National Academy of Sciences, is remarkable because PONV1 has an extraordinarily large genome of 64 kilobases (kb) – making it one of the largest RNA virus genomes ever recorded. 

Pacific oysters are the most widely farmed shellfish worldwide. As the primary shellfish species cultivated in B.C., it has an estimated value of $16 million in 2023. However, they are increasingly affected by mass-mortality events of unknown cause. In 2020, researchers collected 33 oysters from two farms in B.C. and 26 wild oysters from 10 nearby sites. PONV1 was detected in 20 of the dead or dying farmed oysters but was absent in healthy wild oysters, indicating a strong link between the virus and oyster mortality. By interrogating global genetic databases, researchers also found close relatives of PONV1 in Pacific oysters from Europe and Asia, indicating that this group of viruses are globally widespread.

Kevin (Xu) Zhong. Credit: Zhe Cai

Most RNA viruses have small genomes, typically below 30 kb, but PONV1 has a genome size of 64 kb. “The enormous genome of this virus makes it particularly fascinating as it pushes the known boundaries of how big RNA virus genomes can get,” said Dr. Zhong, first author of the study and Research Associate at the Department of Earth, Ocean and Atmospheric Sciences (EOAS) at UBC. “A larger genome may allow the virus to encode more genes or protein domains, potentially expanding or enhancing its ability to interact with hosts. This discovery offers a rare window into the possible evolutionary mechanisms that enable genome expansion in RNA viruses.”

Collecting oysters in a pot. Credit: Amy M. Chan

Farmed oysters with PONV1. Credit: Amy M. Chan

PONV1 and its relatives appear to infect only oysters, so humans are not at risk from contracting the virus, said Dr. Suttle, senior author and Professor at EOAS. “This research is not a cause for alarm. Rather, this is a meaningful step forward in advancing our understanding of oyster health and supporting the long-term sustainability of shellfish aquaculture.”

Curtis Suttle looking at water samples. Credit: Amy M. Chan

Amy Chan (Research Scientist, Suttle Lab) sampling an oyster bed. Credit: Kristi Miller-Saunders

Watch our interview with Dr. Zhong about this discovery:

You can also watch or listen to interviews with Dr. Suttle and Dr. Zhong on CBC On the Coast, Global News, CKNW Jill Bennett Show, Fairchild TV (新時代電視), Cortes Currents. 

Read more about this discovery on Scienmag, Earth.com, National Fisherman, and Glacier Media (via North Shore News, Richmond News, Vancouver is Awesome, Pique NewsMagazine, Times Colonist, Squamish Chief, Business in Vancouver (BIV), Bowen Island Undercurrent, Powell River Peak, and Sechelt / Gibsons Coast Reporter).

Follow more news releases about this discovery here: Evolutionarily divergent nidovirus with an exceptionally large genome identified in Pacific oysters undergoing mass mortality