Viral Gametocytic Hypertrophy of Oysters
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Category
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. Renault (2016) indicated that "the terms papillomalike viruses and polyomalike viruses need to be used as their exact affiliations have yet to be found".
Geographic distribution
Viral gametocytic hypertrophy was reported in Crassostrea virginica from Atlantic Canada, the Eastern U.S., the northeastern Gulf of Mexico coast of Florida and coastal lagoons in the southern Gulf of Mexico, Mexico (Farley 1978, 1985; Meyers 1981; McGladdery 1990, 1999, 2011; McGladdery et al. 1993; Winstead 1998, 2004; Winstead and Courtney 2003; Aguirre-Macedo et al. 2007). Similar lesions were reported from other species of oysters from France (Garcia et al. 2006), Germany (Watermann et al. 2008), Ireland (Cheslett et al. 2009), the west coast of the U.S. (Meyers et al. 2009), Korea (Choi et al. 2004) and Japan (Farley 1985, Arzul et al. 2017). The viral particles described by Cheslett et al. (2009) in Crassostrea gigas in Ireland appear to be similar to those described in C. virginica from the United States and Canada and to those described in C. gigas from Korea and France (Renault 2016).
Host species
Crassostrea virginica, and unconfirmed reports in Crassostrea gigas, Saccostrea (=Crassostrea) commercialis, Crassostrea rhizophorae and Ostrea conchaphila (=Ostrea lurida) (Farley 1985). 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, 2011). 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). Arzul et al. (2017) suggested that the negligible sign of host defense reaction may indicate that the viral particles have a weak impact on oysters.
Diagnostic techniques
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 (Choi et al. 2004, Meyers et al. 2009, McGladdery 2011). Hypertrophied ova had scant cytoplasm and granular nuclear-inclusions that stained Feulgen-positive indicating the presence of DNA (Farley 1985).
Electron microscopy
Presence of icosahedral, non-enveloped viral particles measuring 38-55 nm in diameter in the nucleus of hypertrophied gonadal cells (Farley 1985, Choi et al. 2004, Meyers et al. 2009).
Methods of control
No known methods of prevention or control.
References
Aguirre-Macedo, M.L., R.A. Simá-Álvarez, M.K. Román-Magaña and J.I. Güemez-Ricalde. 2007. Parasite survey of the Eastern oyster Crassostrea virginica in coastal lagoons of the southern Gulf of Mexico. Journal of Aquatic Animal Health 19: 270–279.
Arzul, I., S. Corbeil, B. Morga and T. Renault. 2017. Viruses infecting marine molluscs. Journal of Invertebrate Pathology 147: 118-135.
Cheslett, D., F. Mc Kiernan, C. Hickey and E. Collins. 2009. Viral gametocytic hypertrophy of the Pacific oyster Crassostrea gigas in Ireland. Diseases of Aquatic Organisms 83: 181-185.
Choi, D.L., N.-S. Lee, H.J. Choi, M.-A. Park, S.E. McGladdery and M.S. Park. 2004. Viral gametocytic hypertrophy caused by a papova-like virus infection in the Pacific oyster Crassostrea gigas in Korea. Diseases of Aquatic Organisms 59: 205-209.
Elston, R. 1997. Special topic review: bivalve mollusc viruses. World Journal of Microbiology and Biotechnology 13: 393-403.
Farley, C.A. 1978. Viruses and virus-like lesions in marine molluscs. Marine Fisheries Review 40: 18-20.
Farley, C.A. 1985. Viral gametocytic hypertrophy in oysters. In: C.J. Sindermann (ed.) Identification Leaflets for Diseases and Parasite of Fish and Shellfish, No. 25. ICES, Copenhagen. 5 pp.
Garcia, C., M. Robert, I. Arzul, B. Chollet, J.P. Joly, L. Miossec, T. Comtet and F. Berthe. 2006. Viral gametocytic hypertrophy of Crassostrea gigas in France: from occasional records to disease emergence? Diseases of Aquatic Organisms 70: 193-199.
McGladdery, S. 1990. Shellfish parasites and diseases on the east coast of Canada. Bulletin of the Aquaculture Association of Canada 90 (3): 14-18.
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. CABI Publishing, Wallingford, UK. pp. 723-842.
McGladdery, S.E. 2011. Shellfish diseases (viral, bacterial and fungal), In: Woo, P.T.K., D.W. Bruno (eds.) Fish Diseases and Disorders Second Edition, Volume 3: viral bacterial and fungal infections. CABI Publishing, Wallingford, UK. pp. 748-854.
Meyers, T.R. 1981. Endemic diseases of cultured shellfish of Long Island, New York: adult and juvenile American oysters (Crassostrea virginica) and hard clams (Mercenaria mercenaria). Aquaculture 22: 305-330.
Meyers, T.R., T. Burton, W. Evans and N. Starkey. 2009. Detection of viruses and virus-like particles in four species of wild and farmed bivalve molluscs in Alaska, USA, from 1987 to 2009. Diseases of Aquatic Organisms 88: 1-12.
Renault, T. 2016. Chapter 38 - Papillomalike Viruses and Polyomalike Viruses of Mollusks. In: Kibenge, F.S.B., M.G. Godoy (eds.) Aquaculture Virology. Academic Press, San Diego, pp. 525-526.
Watermann, B.T., M. Herlyn, B. Daehne, S. Bergmann, M. Meemken and H. Kolodzey. 2008. Pathology and mass mortality of Pacific oysters, Crassostrea gigas (Thunberg), in 2005 at the East Frisian coast, Germany. Journal of Fish Diseases 31: 621-630.
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. Journal of Shellfish Research 17: 341-342. (Abstract).
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.
Citation Information
Bower, S.M. (2022): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Viral Gametocytic Hypertrophy of Oysters.
Date last revised: December 2022
Comments to Susan Bower
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