Gill Disease of Portuguese Oyster
Category 1 (Not Reported in Canada)
Common, generally accepted names of the organism or disease agent
Gill disease of Portuguese oysters, Gill necrosis virus disease (GNV), Maladie des branchies.
Scientific name or taxonomic affiliation
Icosahedral DNA virus thought to be an iridovirus but affiliations with the morphologically similar viruses that cause oyster velar virus disease and haemocyte infection virus disease (HIV) are unknown. A protistan, Thanatostrea polymorpha belonging to the Phyla Sarcomastigophora or Labyrinthomorpha, has also been associated with this disease.
France, Portugal, Spain, and Great Britain.
Crassostrea angulata and Crassostrea gigas (cultured in France). Similar clinical signs reported in Ostrea edulis but not identified as the same disease which afflicts C. angulata.
Impact on the host
Extensive gill erosion corresponding with high mortalities. Initial clinical signs of yellow spots on the gills progress to brown discolouration with associated necrosis and degeneration leaving a perforation or V-shaped indentation if the lesion occurred on the edge of the gill. Yellow or green pustules may also occur on the mantle or adductor muscle. Oysters with non-proliferating infections, or in a state of recovery, may show gill lesions but no tissue necrosis. Gill disease is regarded as one factor in the elimination of C. angulata from important culture areas on the Atlantic coast of France. Although active disease has not been reported since 1969, low prevalence was suspected in C. angulata in Portugal in 1999. However, surveys conducted in 2001 and 2002 to identify the etiological agent failed to detect iridoviral infections in Portuguese and French oysters via histology and transmission electron microscopy (Mortensen et al. 2007).
Gross Observations: Preliminary diagnosis can be made on the visible signs as described above.
Histology: Examine for necrosis of gill or labial palp tissue and massive haemocytic cellular infiltration around the lesions. In most lesions, polymorphic hypertrophic cells and hypertrophic globular cells with basophilic, cytoplasmic inclusions are observed.
Electron Microscopy: Cytoplasm of haemocytes or connective tissue cells in the gills containing virogenic stroma and icosahedral enveloped viral particles (350 to 380 nm diameter) with an electron-opaque core (190 nm in diameter). Assembles in cytoplasmic inclusions by budding through de novo membrane at edge of virogenic stroma. No obvious nuclear involvement.
Methods of control
No known methods of prevention or control. Because of the severity of the disease C. angulata is no longer cultured commercially and has been replaced by C. angulata which is more resistant to the disease (Renault and Novoa 2004). Do not move oysters from areas with the disease (currently or historically) to areas where the disease has not been observed.
Alderman, D.J. and P. Gras. 1969. “Gill Disease” of Portuguese oysters. Nature 224: 616-617.
Comps, M. 1969. Observations relatives à l’affection branchiale des huîtres portugaises (Crassostrea angulata Lmk.). Revue des Travaux de l’Institut des Pêches Maritimes 33: 151-160. (In French).
Comps, M. 1980. Mise en évidence par fluorescence du virus de la maladie des branchies de l’huître portugaise Crassostrea angulata Lmk. Sciences et Pêches, Bulletin de l’Institut des Pêches Maritimes 301: 17-18. (In French).
Comps, M. 1985. Maladie des branchies (Gill disease). In: Sindermann, C.J. (ed.) Identification Leaflets for Diseases and Parasites of Fish and Shellfish, No. 23. ICES, Copenhagen, 4 p.
Comps, M. 1988. Epizootic diseases of oysters associated with viral infections. American Fisheries Society Special Publication 18: 23-37.
Comps, M., J.R. Bonami and C. Vago. 1976. Pathologie des invertébrés: une virose de l’huître portugaise (Crassostrea angulata Lmk.). Comptes rendus de l’Académie des Sciences de Paris, Série D 282: 1991-1993. (In French).
Elston, R. 1997. Special topic review: bivalve mollusc viruses. World Journal of Microbiology and Biotechnology 13: 393-403.
Farley, C.A. 1978. Viruses and viruslike lesions in marine mollusks. Marine Fisheries Review 40:18-20.
Franc, A., M. Arvy and P.P. Gras. 1969. Biologie: sur Thanatostrea polymorpha n.g., n.sp., agent de destruction des branchies et des palpes de l’huître portugaise. Comptes rendus de l’Académie des Sciences de Paris, Série D 268: 3189-3190. (In French).
Marteil, L. 1969. La maladie des branchies des huîtres portugaises des côtes françaises de l’Atlantique. Revue des Travaux de l’Institut des Pêches Maritimes 33: 145-150. (In French).
Marteil, L. 1976. La conchyliculture française, 2 partie: biologie de l’huitre et de la moule. Chapitre VI: maladies et mortalites. Revue des Travaux de l’Institut des Pêches Maritimes. 40: 285-313. (In French).
Mortensen, S., I. Arzul, L. Miossec, C. Paillard, S. Feist, G. Stentiford, T. Renault, D. Saulnier and A. Gregory. 2007. Molluscs and crustaceans. In: Raynard, R., T. Wahli, I. Vatsos, S. Mortensen (eds.) Review of disease interactions and pathogen exchange between farmed and wild finfish and shellfish in Europe. VESO on behalf of DIPNET, Oslo. Chapter 5.3.3, pp. 327-328.
Renault, T. and B. Novoa. 2004. Viruses infecting bivalve molluscs. Aquatic Living Resources 17: 397-409.
Bower, S.M. (2001): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Gill Disease of Portuguese Oysters.
Date last revised: February 9, 2009
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