Mikrocytos mimicus n. sp.,
United Kingdom
Information received on 06/12/2013 from Dr Nigel Gibbens, Chief Veterinary Officer, Department for Environment, Food and Rural Affairs, Department for Environment, Food and Rural Affairs, LONDON, United Kingdom
Summary
Report type Immediate notification (Final report)
Date of start of the event 17/05/2013
Date of confirmation of the event 26/06/2013
Report date 06/12/2013
Date submitted to OIE 06/12/2013
Date event resolved 06/09/2013
Reason for notification Emerging disease
Morbidity 40 %
Mortality 40 %
Zoonotic impact No
Causal agent Mikrocytos mimicus n. sp.
New outbreaks (3)
Outbreak 1 (26118) Brancaster, North Norfolk, England
Date of start of the outbreak 17/05/2013
Outbreak status Resolved (06/09/2013)
Epidemiological unit Farm
Water type Salt water
Population type Farmed
Production system Semi-open
Affected animals
Species Morbidity Mortality Susceptible Cases Deaths Killed and disposed of Slaughtered
Pacific Oyster (Crassostrea gigas) (kg) 40 % 40 % 5000 2000 2000 0 0
Affected population Farmed population of triploid Crassostrea gigas, grown in bags on trestle. Adult, market-sized oysters were most affected, with losses in some bags reaching 80%. The infection was not seen in all adult stock on the farm, and some batches remained unaffected. There was a lower observed incidence in juvenile oysters on the site estimated at 20% morbidity and mortality.
Outbreak 2 (26426) Thornham, North Norfolk, England
Date of start of the outbreak 22/05/2013
Outbreak status Resolved (06/09/2013)
Epidemiological unit Farm
Water type Salt water
Population type Farmed
Production system Semi-open
Affected animals
Species Morbidity Mortality Susceptible Cases Deaths Killed and disposed of Slaughtered
Pacific Oyster (Crassostrea gigas) (kg) 20 % 20 % 250 50 50 0 0
Affected population The infection was seen in a small isolated farmed population of triploid Crassostrea gigas, grown in bags on a suspended system. Adult, market-sized oysters were most affected, although some oysters remained unaffected. Around 20% of the oysters harvested from this small farm were affected, and were rejected by the farmer at harvest.
Outbreak 3 (26119) Blakeney Harbour, North Norfolk, England
Date of start of the outbreak 12/06/2013
Outbreak status Resolved (06/09/2013)
Epidemiological unit Farm
Water type Salt water
Population type Farmed
Production system Semi-open
Affected animals
Species Morbidity Mortality Susceptible Cases Deaths Killed and disposed of Slaughtered
Pacific Oyster (Crassostrea gigas) (kg) 20 % 20 % 250 50 50 0 0
Affected population The infection was seen in a small and isolated farmed population of triploid Crassostrea gigas, grown on trestles. Adult, market-sized oysters most affected, although the infection was not seen in all adult stock on the farm, and some batches remained unaffected. Very few oysters were present on this site, which had been fallow for at least a year; the event affected 20% of the stock, none was harvested during the mortality event.
Summary of outbreaks Total outbreaks: 3
Total animals affected
Species Susceptible Cases Deaths Killed and disposed of Slaughtered
Pacific Oyster (Crassostrea gigas) (kg) 5500 2100 2100 0 0
Outbreak statistics
Species Apparent morbidity rate Apparent mortality rate Apparent case fatality rate Proportion susceptible animals lost*
Pacific Oyster (Crassostrea gigas) (kg) 38.18% 38.18% 100.00% 38.18%
*Removed from the susceptible population through death, destruction and/or slaughter
Epidemiology
Source of the outbreak(s) or origin of infection
  • Unknown or inconclusive
Epidemiological comments Movement controls in the form of an initial designation were applied to the individual farm sites, which prevented the onward movement of live oysters for farming or relay. Under the conditions of the designation, movements of Crassostrea gigas were permitted for direct human consumption; subject to hygiene regulations. In addition, the controls stipulated that disposal of dead Pacific oysters Crassostrea gigas of all stages must be by an approved method for disposal of Category 2 animal-by-product waste. The epidemiological investigation has been completed, the designations have been lifted and the incident has been closed. The mortalities occurred from late May and ceased in late July. On the 21st August the oysters were sampled by the Fish Health Inspectorate and showed no evidence of Mikrocytos mimicus or the presence of any listed diseases.
Control measures
Measures applied
  • Movement control inside the country
  • Traceability
  • Official disposal of carcasses, by-products and waste
  • Surveillance within containment and/or protection zone
  • Vaccination prohibited
  • No treatment of affected animals
Measures to be applied
  • Surveillance outside containment and/or protection zone
Diagnostic test results
Laboratory name and type Species Test Test date Result
Centre for Environment, Fisheries and Aquaculture Science (CEFAS) (Regional Reference Laboratory) Pacific Oyster (Crassostrea gigas) histological test 05/06/2013 Positive
Centre for Environment, Fisheries and Aquaculture Science (CEFAS) (Regional Reference Laboratory) Pacific Oyster (Crassostrea gigas) polymerase chain reaction (PCR) 26/06/2013 Positive
Centre for Environment, Fisheries and Aquaculture Science (CEFAS) (Regional Reference Laboratory) Pacific Oyster (Crassostrea gigas) polymerase chain reaction (PCR) 06/09/2013 Negative
Future Reporting
The event is resolved. No more reports will be submitted.
Map of outbreak locations