FIRST DETECTION OF MSX DISEASE (HAPLOSPORIDIUM NELSONI) IN CANADA
(Disease never reported before in Canada).
Information received by OIE on 21 October 2002 from Dr Brian Evans, Executive Director, Canadian Food Inspection Agency, Ottawa:
Report date: 21 October 2002.
Nature of diagnosis: laboratory.
Date of confirmation of infection: 18 October 2002.
Estimated date of first infection: under investigation.
Location : St. Patrick's Channel, Cape Breton, province of Nova Scotia (Atlantic coast)
No. of outbreaks : 1
Description of affected population: American (eastern) oysters Crassostrea virginica.
Total number of animals in the outbreak: samples examined by histology have shown prevalence rates of over 48%, to date. Mortality rates of over 80% have been reported.
A. Laboratories where diagnosis was made:
- The presumptive diagnosis was made by the Shellfish Health Unit, Gulf Fisheries Centre (Fisheries and Oceans Canada), Moncton, province of New Brunswick.
- Diagnosis was confirmed on 18 October 2002 by the Virginia Institute of Marine Science, United States of America (OIE Reference Laboratory for MSX disease), using PCR(1).
B. Diagnostic tests used: histology and PCR(1).
C. Causal agent: Haplosporidium nelsoni. Both plasmodial and sporocyst stages were observed in samples.
A. Source of agent / origin of infection: the source of the infection is unknown. Cases of abnormal mortality and oysters destined for live transfer between Atlantic provinces are routinely examined histologically by shellfish health pathologists at the Gulf Fisheries Centre. No evidence of MSX has been detected in any of these investigations over the last 15 years.
B. Other epidemiological details : oysters on the Pacific coast are considered to be free of the disease as they are predominantly Crassostrea gigas and there is no direct transfer of live oysters between Pacific and Atlantic coasts.
Control measures :
- Contingency plans to control spread of the disease have been implemented by the federal Department of Fisheries and Oceans, in conjunction with provincial authorities.
- Movements of live oysters have been halted and a surveillance programme is under way to determine the geographical extent of infected oyster stocks.
- Efforts are underway to contain the disease and prevent spread to other stocks within Nova Scotia and the southern Gulf of St. Lawrence.
- The feasibility of attempting eradication of the disease is under investigation.
(1) PCR: polymerase chain reaction.
(Source: Disease Information Vol 15 No. 43, 25 October 2002)