Disease data

Mikrocytosis

Previously listed diseases
Molluscs
  • Denman Island disease (Canada)
Protozoan disease; Haplosporidia; Mikrocytos spp.

Summary from the online OIE Diagnostic Manual

Mikrocytosis here refers only to the disease in oysters caused by Mikrocytos mackini on the west coast of Canada. If detected outside the known range of M. mackini , electron microscopy or molecular probes, if available, must be used to identify and distinguish the detected organism from other microcell species ( e.g. Mikrocytos roughleyi, Bonamia ostreae, B. exitiosus) . The presence of these pathogens in any bivalve should be regarded as potentially serious and the OIE Reference Laboratory should be consulted.

Mikrocytos mackini has uncertain taxonomic affinities, but it is not closely related to other microcells ( 8, 10, 11 ) . Mikrocytosis is also known as Denman Island disease ( 2, 13 ) and microcell disease of oysters . Mikrocytos mackini infects Crassostrea gigas, Ostrea edulis and O. conchaphila (= O. lurida); and infects experimentally Crassostrea virginica( 1, 3, 4, 9 ) . Crassostrea gigas seems to be more resistant to the disease than the other species.

Mikrocytos mackini occurs on the south-west coast of Canada. It is probably ubiquitous throughout the Strait of Georgia, including Henry Bay, Denman Island, and is confined to other localities around Vancouver Island ( British Columbia ) .

Mikrocytos mackini produces a focal intracellular infection of muscle and vesicular connective tissue cells, which results in haemocyte infiltration and tissue necrosis ( 5 ) . The parasite may induce yellow-greenish pustules, abscesses and ulcers, mainly on the mantle, with corresponding brown scars on the shell. Macroscopic lesions are not always present. Abscesses are composed of granular haemocytes and hyalinocytes, and may contain small cells of 1-3 µm in diameter. Severe infections appear to be restricted to oysters over 2 years of age.

The mortality rate has been recorded at around 40% for older oysters at low tide levels ( 13 ) . The disease occurs most often in April and May, after a 3-4-month period when temperatures are less than 10°C. Harvesting or moving large oysters to locations high in the intertidal zone prior to March and not planting oysters at lower tide levels before June have been successfully implemented to control the disease ( 1 ) .

For diagnosis, the recommended guidelines for sampling are those stated in Chapter 1.1.4 and Chapter I.2. of this Aquatic Manual.


Countries affected

Country Year Status View Records
Australia 2005 Reported present or known to be present View Records
Canada 2005 Reported present in specific zones View Records
Kuwait 2003 Year of last reported occurrence View Records
UK/ Great Britain 2013 Reported present or known to be present View Records
United States of America 2005 Reported present in specific zones View Records

Species affected

Species Disease occurence Abstract
Crassostrea gigas Natural occurrence OIE Diagnostic Manual for Aquatic Animal Diseases (3rd edition).
Crassostrea gigas Natural occurrence OIE Diagnostic Manual for Aquatic Animal Diseases 2003 (4th edition).
Crassostrea virginica Experimental demonstration OIE Diagnostic Manual for Aquatic Animal Diseases (3rd edition).
Crassostrea virginica Experimental demonstration OIE Diagnostic Manual for Aquatic Animal Diseases 2003 (4th edition).
Ostrea edulis Natural occurrence OIE Diagnostic Manual for Aquatic Animal Diseases (3rd edition).
Ostrea edulis Natural occurrence OIE Diagnostic Manual for Aquatic Animal Diseases 2003 (4th edition).
Ostrea lurida ( = O. conchaphila) Natural occurrence OIE Diagnostic Manual for Aquatic Animal Diseases (3rd edition).
Ostrea lurida ( = O. conchaphila) Natural occurrence OIE Diagnostic Manual for Aquatic Animal Diseases 2003 (4th edition).
Saccostrea ( =Crassostrea ) commercialis Natural occurrence OIE Diagnostic Manual for Aquatic Animal Diseases (3rd edition).
Saccostrea glomerata Natural occurrence World Animal Health in 2003. Part 1. Reports on the animal health status and methods for disease control and prevention. Page 65 (5).
Saccostrea glomerata Natural occurrence OIE Aquatic Animal Health Code 2005 [8th edition]

Countries affected

Country Year Status View Records
Australia 2005 Reported present or known to be present View Records
Canada 2005 Reported present in specific zones View Records
Kuwait 2003 Year of last reported occurrence View Records
UK/ Great Britain 2013 Reported present or known to be present View Records
United States of America 2005 Reported present in specific zones View Records

Species affected

Species Disease occurence Abstract
Crassostrea gigas Natural occurrence OIE Diagnostic Manual for Aquatic Animal Diseases (3rd edition).
Crassostrea gigas Natural occurrence OIE Diagnostic Manual for Aquatic Animal Diseases 2003 (4th edition).
Crassostrea virginica Experimental demonstration OIE Diagnostic Manual for Aquatic Animal Diseases (3rd edition).
Crassostrea virginica Experimental demonstration OIE Diagnostic Manual for Aquatic Animal Diseases 2003 (4th edition).
Ostrea edulis Natural occurrence OIE Diagnostic Manual for Aquatic Animal Diseases (3rd edition).
Ostrea edulis Natural occurrence OIE Diagnostic Manual for Aquatic Animal Diseases 2003 (4th edition).
Ostrea lurida ( = O. conchaphila) Natural occurrence OIE Diagnostic Manual for Aquatic Animal Diseases (3rd edition).
Ostrea lurida ( = O. conchaphila) Natural occurrence OIE Diagnostic Manual for Aquatic Animal Diseases 2003 (4th edition).
Saccostrea ( =Crassostrea ) commercialis Natural occurrence A long-term study of "microcell" disease in oysters with a description of a new genus, Mikrocytos (g. n.), and two new species, Mikrocytos mackini (sp. n.) and Mikrocytos roughleyi (sp. n.).
Saccostrea ( =Crassostrea ) commercialis Natural occurrence OIE Diagnostic Manual for Aquatic Animal Diseases (3rd edition).
Saccostrea glomerata Natural occurrence World Animal Health in 2003. Part 1. Reports on the animal health status and methods for disease control and prevention. Page 65 (5).
Saccostrea glomerata Natural occurrence OIE Aquatic Animal Health Code 2005 [8th edition]