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Haemocytic Infection Virus Disease of Oysters

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Category 1 (Not Reported in Canada)

Common, generally accepted names of the organism or disease agent

Haemocytic infection virus disease (HIV).

Scientific name or taxonomic affiliation

The icosahedral DNA virus associated with haemocytic infection virus disease (HIV) is thought to be an iridovirus but affiliations with the morphologically similar viruses that cause oyster velar virus disease (OVVD) and gill disease in Crassostrea angulata (GNV) are unknown. However, molecular characterization, currently not available, is required to assess their identity (Arzul et al. 2017). As indicated by Renault (2016) the presumptive link to the Iridoviridae is substantial, but definitive demonstration of viral etiology of the diseases must be accomplished by experimental transmission. Because the exact identification of these viruses has not been carried out, the term iridolike viruses needs to be used until their affiliations are established (Renault 2016).

Geographic distribution

France and Spain.

Host species

Crassostrea angulata (Comps et al. 1976; Comps and Duthoit 1976, 1977 (1979)) and a similar but less severe virus infection was reported in Crassostrea gigas (being cultured in France, Comps and Bonami 1977, Comps 1988).

Impact on the host

Haemocytic infection virus (HIV) disease caused mass mortalities of C. angulata in Marenner Oleron and Brittany, France from 1970 to 1973 (Comps et al. 1976, Comps 1988, Renault 1996, Elston 1997, Renault and Novoa 2004). This disease outbreak was followed by a report of a similar type of virus infection in C. gigas in the Bay of Arcachon, France in 1977, long after the disappearance of C. angulata in that area (Comps and Bonami 1977, Comps 1988, Elston 1997, Renault 2016). High mortality rates led to the almost total extinction of C. angulata in French Atlantic waters in 1973 (Renault and Novoa 2004, Arzul et al. 2017). However, C. gigas seemed to be resistant to HIV and, after the disappearance of C. angulata, replaced the latter species in France (Renault 2016).

Unlike GNV which is associated with the gill epithelium, HIV occurs in the connective tissue including the haemocytes and the pathology of each diseases is distinctive (Renault and Novoa 2004). However, in both diseases, the virus is found in the cytoplasm of infected cells (Comps and Duthoit 1977 (1979)). In 1977, a disease that caused a 15% mortality in C. gigas kept in a purification plant in the Bay of Arcachon was associated with a virus morphologically similar to HIV (Comps and Bonami 1977). As was the case for C. angulata, affected C. gigas exhibited virtually no external signs of disease, except for a greyish discoloration of the visceral mass in some cases. Histological examination, however, revealed considerable degeneration of connective tissues and the presence of atypical cells interpreted as infected haemocytes (Renault and Novoa 2004).

Haemocytic infection virus (HIV) was most recently detected (by tissue imprints, histology and transmission electron microscopy) in 1983 and 1984 in Brittany associated with a mass mortality of C. angulata following their re-introduction for culture purposes (Bougrier et al. 1986). Renault (2016) indicated that the pathogenicity of HIV and GNV have not been experimentally demonstrated, nevertheless, these viruses have been identified as the most probable cause of recurrent mass mortalities of C. angulata observed in Europe since 1966.

Diagnostic techniques

Gross observations

Atrophy and weakness of the adductor muscle and grayish discolouration of the viseral mass of some C. gigas (Renault and Nova 2004, Renault 1996). However, no distinctive clinical signs were associated with the disease including no gill lesions (Elston 1997, Renault 2016, Arzul et al. 2017).


Haemocytic infection virus (HIV) induces cytoplasmic lesions in the haemocytes and causes severe injuries to interstitial tissues (Comps 1988). Specifically, considerable degeneration of the connective tissues including acute inflammatory response associated with the presence of atypical haemocytes with pycnotic nuclei and round basophilic, Feulgen positive, intracytoplasmic inclusion bodies (2-3 µm in diameter) in the connective tissue and an increase in the number of brown cells is evident (Comps et al. 1976; Comps and Duthoit 1976; Comps 1988; Renault 1996, 2016; Arzul et al. 2017). Because the virus was not isolated from oysters nor characterized chemically, the presence of deoxyribonucleic acid (DNA) in the virus was demonstrated by histochemical techniques (Comps 1988). Renault (2016) provided a description and figure of an atypical haemocyte in C. angulata infected with HIV.

Electron microscopy

Haemocyte inclusions corresponded to virogenic stroma and the cytoplasm also contained icosahedral viral particles (350-380 nm in diameter) with a capsid and containing an electron-opaque core/dense core (190-250 nm in diameter) (Comps and Duthoit 1976, Comps and Bonami 1977, Comps 1978, Renault 1996). The virons are assembled in cytoplasmic inclusions by budding through de novo membrane at edge of virogenic stroma (Comps et al. 1976; Comps and Duthoit 1976, 1977 (1979); Comps 1978; Elston 1997). In C. gigas, virons were associated with cytoplasmic paracrystaline arrays.

Methods of control

No known methods of prevention or control. Crassostrea angulata is no longer cultured commercially and has been replaced by C. gigas which seems to be more resistant to the disease. Do not move oysters from areas with the disease (currently or historically) to areas where the disease has not been observed.


Comps, M. 1978. Évolution des recherches et études récentes en pathologie des huîtres. Oceanologica Acta 1: 255-262.

Comps, M. 1988. Epizootic diseases of oysters associated with viral infections. American Fisheries Society Special Publications 18: 23-37.

Comps, M. and J.-R. Bonami. 1977. Infection virale associée à des mortalités chez l'huître Crassostrea gigas Thunberg. Comptes Rendus Académie des Sciences de Paris, Série D 285: 1139-1140. (in French only)

Comps, M. and J.-L. Duthoit. 1976. Infection virale associée à la "maladie des branchies" de l'huître portugaise Crassostrea angulata LmK. Comptes Rendus Académie des Sciences de Paris, Série D 283: 1595-1597. (in French only)

Comps, M. and J.-L. Duthoit. 1977 (1979). Infections virales chez les huîtres Crassostrea angulata Lmk. et Crassostrea gigas Th. Haliotis 8: 301-307. (in French only)

Comps, M., J.-R. Bonami, C. Vago and A. Campillo. 1976. Une virose de l'huître portugaise (Crassostrea angulata LMK). Comptes Rendus Académie des Sciences de Paris, Série D 282: 1991-1993. (in French only)

Elston, R.A. 1993. Infectious diseases of the Pacific oyster, Crassostrea gigas. Annual Review of Fish Diseases 3: 259-276.

Elston, R. 1997. Special topic review: bivalve mollusc viruses. World Journal of Microbiology and Biotechnology 13: 393-403.

Renault, T. 1996. Appearance and spread of disease among bivalve molluscs in the northern hemisphere in relation to international trade. Revue Scientifique et Technique de l'Office International des Epizooties 15: 551-561. (in French only)

Renault, T. 2016. Chapter 36 - Iridolike viruses of mollusks, In: Kibenge, F.S.B., M.G. Godoy (eds.) Aquaculture Virology. Academic Press, San Diego, pp. 507-512.

Renault, T. and B. Novoa. 2004. Viruses infecting bivalve molluscs. Aquatic Living Resources 17: 397-409.

Citation Information

Bower, S.M. (2022): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Haemocytic Infection Virus Disease of Oysters.

Date last revised: October 2022
Comments to Susan Bower

Date modified: