Haemocytic Neoplasia of Oysters


Category 1 (Not Reported in Canada)

Common, generally accepted names of the organism or disease agent

Haematopoietic, Hemic or Haemocytic neoplasia, HCN, Disseminated neoplasia.

Scientific name or taxonomic affiliation

Unknown aetiology, the progenitor cell type has not been firmly established. Thus, the more conservative name of disseminating neoplasia is probably more appropriate for this disease.

Geographic distribution

Europe, Chile, Australia, Japan, Philippines and the Atlantic, Pacific, and Gulf coasts of the U.S. This disease has not been reported from oysters in Canada but a similar condition of unknown cause is prevalent in mussels on the west coast and rare in mussels and soft-shell clams on the east coast of Canada.

Host species

Crassostrea virginica, Crassostrea gigas (reports rare), Crassostrea iredalei, Ostrea edulis, Ostrea (=Ostreola) conchaphila (=lurida), Saccostrea commercialis, Tiostrea (=Ostrea) chilensis; (clams, and mussels also affected).

Impact on the host

Gradual appearance of neoplastic haemocytes throughout the soft tissues with associated disruption of normal function of the haemocytes. Neoplastic condition totally unrelated to human neoplasias but similar to leukemia in the way it affects the bivalve. The disease has been recorded from several populations which suffer no directly associated mortality. In populations where mortalities occur annually, 30-50% may be lost, predominantly over the fall and winter. In most populations, the prevalence is very low (e.g., 12 of 20,000 C. virginica surveyed from the Maryland portion of Chesapeake Bay over a 14 year period as reported by Harshbarger et al. (1977); 184 of 45,000 O. edulis surveyed from the Breton coasts of France over a 6 year period (Balouet et al. 1986); and 3% of C. iredalei with no associated mortality at a demonstration farm near Dagupan City, Philippines (De Vera et al. 2005)). Susceptibility to infection may be associated with oyster genetics. Frierman and Andrews (1976) found elevated prevalence in two laboratory produced strains of C. virginica (8.4%) compared to wild C. virginica (0.08%). It does appear that the disease is infectious, and up to 100% of intensively cultured bivalves can be affected. The unusually high prevalence after gametogensis in a single year class of C. virginica from lower Delaware Bay, New Jersey, USA was associated with an exceptionally heavy setting of that year class suggesting that extreme crowding may have stressed the oysters and would have fostered transmission of a putative infectious agent (Ford et al. 1997). The suggestion that these neoplasias may be virus-related has yet to be proven. To date, there has been no consistent correlation found between pollution and the occurrence of HCN.

Diagnostic techniques

Histocytology (Haemocytology): Examine haemocytes for characteristics described below. The diseased haemocytes round up and lack pseudopodial adhesion to the slide.

Histology: Intense infiltration of abnormal haemocytes (hypertrophied with very little cytoplasm in relation to nucleoplasm and with enlarged and often pleomorphic nuclei containing one or more prominent nucleoli) and the presence of obvious mitotic figures. Mass proliferation of haemocytes may result in diapedesis of large clumps of cells and/or vascular occlusion in the most severe cases and possibly disruption of normal tissue.

Methods of control

Due to the clearly demonstrated contagious nature of HCN, every effort should be taken to avoid introducing infected stock (current or historically). To date, the possibility of cross-transmission (between species of bivalves) has not been clearly demonstrated. The effect of the disease can be reduced by maintaining cultivated populations at as low a density as practical; harvesting prior to the typical period of increased mortality (fall and winter); harvesting stocks as young as possible (since the severity of infection appears to increase with age).


Alderman, D.J., P. van Banning and P. Colomer. 1977. Two European oyster (Ostrea edulis) mortalities associated with an abnormal hemocytic condition. Aquaculture 10:335-340.

Balouet, G., M. Poder, A. Cahour and M. Auffret. 1986. Proliferative hemocytic condition in European flat oysters (Ostrea edulis) from Breton coasts: a 6-year survey. Journal of Invertebrate Pathology 48: 208-215.

Barber, B.J. 2004. Neoplastic diseases of commercially important marine bivalves. Aquatic Living Resources 17: 449-466.

Bower, S.M. 1989. The summer mortality syndrome and haemocytic neoplasia in blue mussels (Mytilus edulis) from British Columbia. Canadian Technical Report of Fisheries and Aquatic Sciences 170: 1-65.

De Vera, A.Z., S.E. McGladdery, A.A. Herrera, M.F. Stephenson, M. Maillet and D. Bourque. 2005. Occurrence of hemic neoplasia in slipper oyster, Crassostrea iredalei (Faustino, 1928), in Dagupan City, Philippines. In: Walker, P.J., R.G. Lester, M.G. Bondad-Reantaso (eds.) Diseases in Asian Aquaculture V. Proceedings of the 5th Symposium on Diseases in Asian Aquaculture, Manila. pp. 321-325.

Elston, R.A., J.D. Moore and K. Brooks. 1992. Disseminated neoplasia of bivalve molluscs. Reviews in Aquatic Sciences 6: 405-466.

Farley, C.A. 1976. Proliferative disorders in bivalve molluska. Marine Fisheries Review 38(10): 30-33.

Ford, S.E., R.D. Barber and E. Marks. 1997. Disseminated neoplasia in juvenile eastern oysters Crassostrea virginica, and its relationship to the reproductive cycle. Diseases of Aquatic Organisms 28: 73-77.

Frierman, E.M. and J.D. Andrews. 1976. Occurrence of hematopoietic neoplasms in Virginia oysters (Crassostrea virginica). Journal of the National Cancer Institute 56(2): 319-324.

Harshbarger, J.C., S.V. Otto and S.C. Chang. 1977 (1979). Proliferative disorders in Crassostrea virginica and Mya arenaria from the Chesapeake Bay and intranuclear virus-like inclusions in Mya arenaria with germinomas from a Maine oil spill site. Haliotis 8: 243-248.

Mix, M.C. 1975. Proliferative characteristics of atypical cells in native oysters (Ostrea lurida) from Yaquina Bay, Oregon. Journal of Invertebrate Pathology 26: 289-298.

Mix, M.C. and W.P. Breese. 1980. A cellular proliferative disorder in oysters (Ostrea chilensis) from Chiloe, Chile, South America. Journal of Invertebrate Pathology 36:123-124.

Peters, E.C. 1988. Recent investigations on the disseminated sarcomas of marine bivalve molluscs. American Fisheries Society Special Publication 18: 74-92.

Citation Information

Bower, S.M., McGladdery (2006): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Haemocytic Neoplasia of Oysters.

Date last revised: December 2006
Comments to Susan Bower

Date modified: