Infection with Haplosporidium nelsoni

What is Haplosporidium nelsoni?

Haplosporidium nelsoni causes multinuclear sphere X (MSX) disease in cultured and wild American oysters.

What species of molluscs can be infected by Haplosporidium nelsoni?

Each species of molluscs may have several common names but only one common name is listed.

Species susceptible to Haplosporidium nelsoni that exist in the natural environment in Canada include:

• Crassostrea gigas (Pacific cupped oyster)
• Crassostrea virginica (American oyster)

Is Haplosporidium nelsoni a risk to human health?

No. The causal agent of Haplosporidium nelsoni is not a risk to human health.

What are the signs of Haplosporidium nelsoni?

Haplosporidium nelsoni causes disease in oysters. It is a cause of mortality in juvenile and adult oysters.

• Oysters that are over 2 years old are particularly affected.
• Mortality rates can reach 90% to 95% in older oysters.

 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

Is Haplosporidium nelsoni found in Canada?

Yes. In Canada, Haplosporidium nelsoni has been found in Nova Scotia and British Columbia.

How is Haplosporidium nelsoni spread?

The complete life cycle of Haplosporidium nelsoni is not known. Therefore, how infection is spread between molluscs is unknown.

However, it is likely that people can spread Haplosporidium nelsoni by moving infected molluscs and contaminated equipment.

How is Haplosporidium nelsoni diagnosed?

Diagnosis of an infection with Haplosporidium nelsoni requires the identification of the parasite through laboratory tests. Not all infected molluscs show signs of disease.

How is Haplosporidium nelsoni treated?

There are no treatment options currently available for Haplosporidium nelsoni.

What measures can be taken to prevent the introduction and spread of Haplosporidium nelsoni?

If you frequently handle or work with molluscs, be aware of the clinical signs of Haplosporidium nelsoni.

Do not import live infected molluscs into Canada.

• An import permit is required from the Canadian Food Inspection Agency (CFIA) for certain species of molluscs as of December 2011.
• People bringing molluscs into Canada should check other federal, provincial, and/or territorial requirements before entering the country.

Do not introduce live molluscs from another country into the natural waters of Canada.

• People releasing molluscs into the natural waters or rearing facilities within Canada should check if federal or provincial and/or territorial permits are required.

If you frequently handle or work with molluscs, be aware of where Haplosporidium nelsoni occurs in your area.

• A federal, provincial and/or territorial permit or licence may be required to relocate molluscs within Canada.

Do not use molluscs that were bought in a grocery store as bait for catching fish or other aquatic animals.

Shells that are removed from molluscs or unwanted molluscs that you harvested or bought for your consumption should be disposed of in your municipal garbage.

The CFIA recommends 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.

Wash and disinfect the footwear you wore to the site or when you had contact with wild molluscs. Also wash your clothing thoroughly and dry it at a high temperature.

What is done to protect Canadian aquatic animals from Haplosporidium nelsoni?

Haplosporidium nelsoni is a reportable disease in Canada. This means that anyone who owns or works with aquatic animals, who knows of or suspects Haplosporidium nelsoni in their molluscs, is required by law to notify the CFIA.

If Haplosporidium nelsoni is found in Canada, the CFIA would control its spread by implementing disease response activities. These may include

• controlling the movements of infected animals that people own or work with
• humanely destroying infected animals
• cleaning and disinfecting

The control measures chosen would depend on the situation.

What do I do if I think molluscs that I am raising or keeping have Haplosporidium nelsoni?

If you suspect that molluscs you are raising or keeping may have Haplosporidium nelsoni, you are required under the Health of Animals Act to immediately notify the CFIA of your suspicion.

How do I get more information

For more information about reportable diseases, visit the Aquatic Animal Health page, contact your local CFIA Animal Health Office, or your CFIA Area office:

• Atlantic: 506-777-3939
• Quebec: 514-283-8888
• Ontario: 226-217-8555
• West: 587-230-2200