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
- Susceptibility
- Clinical signs
- Diagnosis and treatment
- Transmission and spread
- Disease management
- 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/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.
Disease management
MSX is a reportable disease in Canada. This means that anyone who owns or works with aquatic animals and knows of or suspects MSX in their molluscs, is required by law to notify us.
We have several programs in place to prevent the spread of this disease. This includes the Domestic Movement Control Program (DMCP), as well as responding to and investigating all suspected cases of MSX reported to us.
The following watersheds are declared infected for MSX:
- Atlantic Ocean
- British Columbia North
- British Columbia South
- Quebec
- New Brunswick
- Newfoundland and Labrador
- Nova Scotia
- Pacific Ocean North
- Pacific Ocean South
- Prince Edward Island
Confirmed cases of federally reportable aquatic animal diseases in Canada, like MSX, are reported monthly on our website.
Preventative measures
Do not import live molluscs or mollusc products into Canada without proper permissions
An 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 (AIRS).
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 our import requirements can be found in AIRS.
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 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 molluscs.