Detections of MSX and Dermo in Canada
We are responding to detections of Multinucleate sphere unknown (MSX) and/or Dermo in oysters in Prince Edward Island, New Brunswick, and Nova Scotia.
Multinucleate sphere unknown (MSX) is a disease in oysters caused by the parasite Haplosporidium nelsoni. It is a serious disease that can cause significant mortality of both cultured and wild oysters.
MSX is not a risk to food safety or human health.
On this page
- Impact on oysters
- Clinical signs
- Susceptibility
- Diagnosis and treatment
- Transmission and spread
- Surveillance and detections
- Preventative measures
Impact on oysters
MSX causes mortality in juvenile and adult oysters. Oysters that are over 2 years old are more affected, and mortality rates can reach 90% to 95%. Juvenile oysters (seed and spat) can be heavily infected with MSX spores.
Susceptibility
Species susceptible to MSX that exist in the natural environment in Canada include:
- Crassostrea gigas (Pacific cupped oyster)
- Crassostrea virginica (American oyster)
Clinical signs
Affected molluscs may exhibit any of the following signs:
- behaviour
- valves slow to close when disturbed
- appearance
- decreased rate of growth
- no new shell growth
- extensive fouling along the inside peripheral left valve
- juvenile oysters may have pale digestive glands
- oysters appear thin and watery
- receding of the mantle
- raised yellow-brown spots on internal valve surfaces
Diagnosis and treatment
Diagnosis of an infection with Haplosporidium nelsoni requires the identification of the parasite through laboratory tests. Polymerase chain reaction (PCR) testing is the first step in the testing process, and infection is confirmed with genetic sequencing and visualization of the parasite using histopathology. Not all infected oysters show signs of disease.
There are no treatment options currently available for MSX.
Transmission and spread
The complete life cycle of Haplosporidium nelsoni is not known. Therefore, how MSX is spread between oysters is unknown. However, it is likely that MSX can be spread by moving infected oysters and contaminated equipment.
Surveillance and detections
MSX is a reportable disease in Canada. This means that anyone who owns or works with aquatic animals, who knows of or suspects MSX in their molluscs, is required by law to notify us.
We have several programs in place to prevent the introduction and spread of this disease. This includes the Domestic Movement Control Program (DMCP), yearly surveillance sampling, as well as responding to and investigating all suspected cases of MSX reported to us.
We have previously declared infected areas in the following watersheds:
- Atlantic Ocean Central
- Cape Breton East
- British Columbia North
- British Columbia South
- Pacific Ocean North
- Pacific Ocean South
Preventative measures
The following preventative measures are recommended for anyone who handles or works with oysters. Additionally, guidance on how to prevent the spread of MSX from primary control zones (PCZs) to other locations within Canada is available: MSX biosecurity guidelines for PCZs.
Do not import live molluscs or mollusc products into Canada without proper permissions
A CFIA aquatic animal health import permit, zoosanitary certificate or other documentation may be required to import aquatic animals into Canada. Consult the susceptible species of aquatic animals for guidance on import requirements.
Importers must follow the import permit conditions to prevent the introduction and spread of diseases. Additional information on import requirements and the countries approved to export to Canada can be found in the Automated Import Reference System.
People bringing molluscs into Canada should check all federal, provincial, and/or territorial requirements before entering the country.
Do not introduce live molluscs or mollusc products from another country into the natural waters of Canada without proper permissions
People releasing molluscs into the natural waters or rearing facilities within Canada should check if federal, provincial, or territorial permissions are required.
Information on CFIA import requirements can be found in the Automated Import Reference System.
Properly dispose of oysters
Shells that are removed from oysters or unwanted oysters that you harvested or bought for your consumption should be disposed of in your municipal garbage or compost (if land-based).
Do not use oysters as bait
Do not use molluscs that were bought in a grocery store as bait for catching fish or other aquatic animals.
Wash and disinfect gear and equipment
Wash and disinfect any gear you wore (for example, footwear, gloves, waders, etc.) after being on-site or handling wild oysters. Thoroughly wash and disinfect your gear (for example, tongs, cages, bins, etc.) and air dry them.
Take precautions after travelling
We recommend that you do not visit Canadian aquaculture sites, zoos or aquariums for 14 days if you have travelled to another country and visited an aquaculture site or had contact with wild molluscs.