Concomitant herpes-like virus infections in hatchery-reared larvae and nursery-cultured spat Crassostrea gigas and Ostrea edulis

Abstract

Concomitant sporadic high mortalities were reported in France in May 1994 among batches of hatchery-reared larval Pacific oysters Crassostrea gigas and European flat oysters Ostrea edulis in 2 hatcheries, and in June and July 1994 among batches of cultured spat of both species in a shellfish nursery. Histological observation showed the presence of cellular abnormalities in moribund animals. Transmission electron microscopy revealed the presence of herpes-like virus particles in infected larvae and spat of both oyster species. This is the first description of a herpes-like virus infection in larval O. edulis. Viruses observed in diseased larvae and spat of both species are similar with respect to ultrastructure and morphogenesis. They were detected simultaneously in C. gigas and O. edulis larvae and spat, indicating possible interspecific transmission. Moreover, these viruses are associated with high mortality rates in both oyster species. An electron microscopic examination revealed hemocytes with condensed chromatin and extensive perinuclear fragmentation of chromatin. These data suggest that herpes-like viruses infecting oysters may induce apoptosis in oyster hemocytes. KEY WORDS: Herpes-like virus · European flat oyster · Ostrea edulis · Pacific oyster · Crassostrea gigas · Oyster mortality · Concomitant infection · Virus replication · Apoptosis Resale or republication not permitted without written consent of the publisherDis Aquat Org 42: [173][174][175][176][177][178][179][180][181][182][183] 2000 viral particles reported by Hine et al. (1992) in New Zealand and the virus-like particles described by Comps & Cochennec (1993) among French cultured European flat oyster spat.We describe for the first time a herpes-like virus infecting European flat oyster larvae and concomitant herpes-like virus infections associated with high mortalities among hatchery-reared larvae and nurserycultured spat of both Crassostrea gigas and Ostrea edulis during the summer of 1994 in France. We performed an ultrastructural comparative study between both virus-like particles found respectively in Pacific oysters and European flat oysters and compared them to viruses belonging to the Herpesviridae family. MATERIALS AND METHODS Specimens.Larval Ostrea edulis and Crassostrea gigas, 6 to 10 d old, 80 to 150 µm in size, were collected in May 1994 from 2 hatcheries located in Bourgneuf Bay (Vendée, France). Nursery-cultured spat of C. gigas and O. edulis, 3 to 5 mo old, were also collected from Bourgneuf Bay in June and July 1994.Light microscopy. A total of 197 European flat oyster spat and 196 Pacific oyster spat were collected for light microscopical examination. Moribund cultured spat of both species, 3 to 5 mo old, were removed from the shell and, sagittally sectioned; then half of each specimen was fixed in Davidson's fixative for light microscopic examination and the other half in Carson's fixative for transmission electron microscopic analysis. After 48 h fixation in Davidson's fluid, samples were dehydrated using an ...

Purification and partial genome characterization of a herpes-like virus infecting the Japanese oyster, Crassostrea gigas.

“…For negative staining, a small piece of pellet was resuspended in filtered (0n2 µm) sea water, particles were adsorbed on collodion-coated 200 mesh copper grids and negatively stained using filtered (0n2 µm) 2 % phosphotungstic acid (PTA). A small piece of each pellet was also fixed in 3 % glutaraldehyde in 0n2 M cacodylate buffer (pH 7n2), post-fixed with 1 % osmium tetroxide in the same buffer and embedded in Epon resin using methods already described (Renault et al, 1994 b). Ultrathin sections were contrasted with uranyl acetate and lead citrate, using conventional methods.…”

“…Ultrathin sections were contrasted with uranyl acetate and lead citrate, using conventional methods. C. gigas larvae were treated as above, but a decalcification step in a solution of 5 % EDTA was performed prior to Epon embedding (Renault et al, 1994 b). Observations were performed using a JEOL JEM 1200EX transmission electron microscope operating at 60 kV.…”

“…each year during the summer period in association with the detection of a herpes-like virus (Renault et al, 1994 b). Three to four days after the spond, reduction in larval feeding and swimming activities are observed.…”

“…The first was observed in Crassostrea virginica (Farley et al, 1972). Subsequently, herpes-like viruses in other cultivated oyster species, such as Crassostrea gigas (Hine et al, 1992 ;Nicolas et al, 1992 ;Renault et al, 1994 b) and Ostrea edulis (Comps & Cochennec, 1993), have been found to be associated with high mortality rates. More recently, other herpes-like virus infections have been described in Ostrea angasi adults (Hine & Thorne, 1997) and in Tiostrea chilensis larvae (Hine, 1997).…”

“…Three to four days after the spond, reduction in larval feeding and swimming activities are observed. Significant mortality occurs by day 6, with 100 % mortality by day 8-12 in most affected batches (Renault et al, 1994 b).…”