Viral Gametocytic Hypertrophy of Oysters
Category 2 (In Canada and of Regional Concern)
Common, generally accepted names of the organism or disease agent
Viral gametocytic hypertrophy, VGH, Ovacystis disease.
Scientific name or taxonomic affiliation
Pathology has been associated with a papilloma-like virus (also referred to as papova-like and polyoma-like viruses) with morphological characteristics similar to those of the Papillomaviridae and Polyomarviridae families.
InCrassostrea virginica from Atlantic Canada, the Eastern U.S. and the northeastern Gulf of Mexico coast of Florida. Similar lesions reported from other species of oysters from the west coast of the U.S., Korea and Japan.
Crassostrea virginica, and unconfirmed reports in Crassostrea gigas, Saccostrea (=Crassostrea) commercialis, Crassostrea rhizophorae and Ostrea conchaphila (=Ostrea lurida). Other bivalves including Pinctada maxima and Mya arenaria were reported to be infected by papova-like viruses.
Impact on the host
Causes massive hypertrophy of individual gametes and gametogenic epithelium by replicating in the host cell nucleus. Host response to infection is negligible to a light to moderate haemocyte infiltration into localised areas adjacent to infected gametes. Level of infection generally low (usually fewer than five infected cells per 6 µm tissue section) but prevalence of infection up to 80% occur sporadically (McGladdery 1999). In Atlantic Canada, this infection is also found in immature oysters where germinal cells are infected (McGladdery et al. 1993). Despite the massive hypertrophy and tissue displacement surrounding infected cells, no adverse effect on oyster health or fecundity, and no indication of associated mortality was detected (McGladdery 1999). Experimental investigation is required to determine if the virus could adversely affect hatchery broodstock productivity (McGladdery et al. 1993).
Histology: Examine transverse sections through the gonad and observe abnormally enlarged basophilic (with haematoxylin and eosin stain) or Feulgen positive hypertrophic ova (up to 500 µm in diameter), sperm and germinal cells. Hypertrophied ova had scant cytoplasm and granular nuclear-inclusions that stained Feulgen-positive indicating the presence of DNA.
Electron Microscopy: Presence of icosahedral, non-enveloped viral particles measuring 43-55 nm in diameter in the nucleus of hypertrophied gonadal cells.
Methods of control
No known methods of prevention or control.
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McGladdery, S.E., R.E. Drinnan and M.F. Stephenson. 1993. A manual of parasites, pests and diseases of Canadian Atlantic bivalves. Canadian Technical Report of Fisheries and Aquatic Sciences 1931: 1-121 (specifically pg. 53-55).
McGladdery, S.E. 1999. Shellfish diseases (viral, bacterial and fungal). In: Woo, P.T.K., D.W. Bruno (eds.) Fish Diseases and Disorders, Volume 3: Viral, Bacterial and Fungal Infections, Vol. 3. CABI Publishing, Wallingford, UK. pp. 723-842.
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Winstead, J.T. and L.A. Courtney. 2003. Ovacystis-like condition in the eastern oyster Crassostrea virginica from the northeastern Gulf of Mexico. Diseases of Aquatic Organisms 53: 89-90.
Winstead, J.T., R.M. Overstreet and L.A. Courtney. 1998. Novel gonadal parasites in the eastern oyster Crassostrea virginica from two Gulf of Mexico bays. (Abstract). Journal of Shellfish Research 17: 341-342.
Winstead, J.T., A.K. Volety and S.G. Tolley. 2004. Parasitic and symbiotic fauna in oysters (Crassostrea virginica) collected from the Caloosahatchee River and estuary in Florida. Journal of Shellfish Research 23: 831-840.
Bower, S.M. (2009): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Viral Gametocytic Hypertrophy of Oysters.
Date last revised: February 2010
Comments to Susan Bower
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