Detections of MSX and Dermo in oysters in Quebec
OTTAWA, ON, July 4, 2025 /CNW/ - The Canadian Food Inspection Agency (CFIA) has confirmed the presence of the aquatic animal diseases multinucleate sphere unknown (MSX) and Dermo (also known as Perkinsosis) in oyster samples collected in Chaleur Bay, Québec.
MSX and Dermo do not pose risks to human health or food safety, but they can cause increased oyster mortality and decreased growth rates. These are the first confirmed cases of MSX and Dermo in Quebec.
To limit the spread of the diseases, the CFIA, Fisheries and Oceans Canada (DFO) and the province of Quebec are working together with partners to monitor the situation and take necessary action. These actions are part of the Government of Canada's One Health approach to prepare for, detect, and manage animal diseases.
In addition to existing robust protective measures and increased animal surveillance, the CFIA, in collaboration with DFO and the province of Quebec, continues to conduct tracing activities and testing of oysters to gain insight into the presence of MSX and Dermo in the area.
Response measures include:
- applying movement controls to oysters,
- further investigating the potential source of the detections,
- engaging scientists, producers and harvesters to continue to monitor mollusc health, including notifying CFIA or the province of sick oysters or when decreased rates of growth or increased mortalities are observed, and
- ensuring that information regarding detection and movement control information is available to producers.
Quick Facts
- MSX and Dermo pose no risk to human health and are not food safety concerns.
- Haplosporidium nelsoni causes multinucleate sphere unknown (MSX) in cultured and wild American oysters (Crassostrea virginica).
- Perkinsus marinus causes Perkinsosis (also known as Dermo) in cultured and wild American oysters (Crassostrea virginica).
- These diseases do not affect other bivalves in this area, including mussels, scallops, or clams; however, they can cause increased oyster mortality and decreased growth rates.
- With MSX, it is presumed there is an unknown intermediary host which makes it harder to determine how it is spread. Dermo can be transmitted from oyster to oyster, or from water contaminated with the parasite.
- Canada'sNational Aquatic Animal Health Program (NAAHP), co-delivered by the CFIA and Fisheries and Oceans Canada (DFO), is responsible for preventing the introduction and/or spread of significant aquatic animal diseases of finfish, molluscs and crustaceans.
Related links
- Response to MSX and Dermo in oysters – Canadian Food Inspection Agency
- Haplosporidium nelsoni (MSX) disease information – Fisheries and Oceans Canada
- Perkinsus marinus ("Dermo" Disease) of Oysters – Fisheries and Oceans Canada
- National Aquatic Animal Health Program
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Each day, hard-working Canadian Food Inspection Agency employees—including inspectors, veterinarians, and scientists—inspect food for safety risks, work to protect plants from pests and invasive species, and respond to animal diseases that could threaten Canada's animal resource base and human health. Guided by science-based decision-making and modern regulations, the Agency verifies that food sold in Canada is safe while supporting access to international markets for our high-quality agricultural products. To learn more, visit inspection.canada.ca
SOURCE Canadian Food Inspection Agency (CFIA)