Description of a presumptive hepatopancreatic reovirus, and a putative gill parvovirus, in the freshwater crayfish Cherax quadricarinatus

The redclaw freshwater crayfish Cherax quadricarinatus has a reputation for being hardy and resistant to handling stress. However, in recent years, possibly since 1996, C. quadricarinatus farmers in northern Queensland have noted a decrease in stress resistance in their stock. A presumptive reovirus in the hepatopancreas, and a putative parvovirus in the gills, were associated with chronic mortalities in C. quadricarinatus at one northern Queensland farm. Hypertrophic nuclei with marginated chromatin were observed in gill epithelium in moribund crayfish which had recently been relocated to a laboratory from the holding tank facility on the farm. Affected nuclei appeared to be vacant or contained a faint granular basophilia in H&E stained sections. However, toluidine blue staining revealed a homogeneously granular appearance of the nuclei. Transmission electron microscopy revealed approximately 20 nm diameter virus-like particles within the nucleus. Eosinophilic, Feulgen-negative, cytoplasmic inclusions were observed in distal hepatopancreatocytes in 1 moribund C. quadricarinatus collected from the same on-farm holding tank approximately 6 mo later. This crayfish did not display the gill lesions. Transmission electron microscopy showed that the inclusions contained icosahedral virus particles 35 to 40 nm in diameter. The histopathology and preliminary virus morphology of the presumptive hepatopancreatic reovirus, and the histopathology, ultrastructural pathology and preliminary virus morphology of the putative gill parvovirus, are reported herein.     

Pathology of cultured paua Haliotis iris infected with a novel haplosporidian parasite,with some observations on the course of disease

Mortalities among juvenile paua Haliotis iris Martyn 1784 in a commercial culture facility were reported in April 2000. Histology of moribund paua showed heavy systemic infections of a uni- to multi-nucleate stage of a novel organism later confirmed by transmission electron microscopy (TEM) and molecular studies to be a haplosporidian. Multinucleate plasmodia up to 25 microm diameter with up to 17 nuclei were detectable in wet preparations of hemolymph from heavily infected paua. The presence of the haplosporidian in the affected facility was associated with mortalities of slow growing 'runt' paua during the summer months. Total mortalities in affected raceways 6 mo after mortalities began were between 82.5 and 90%. Heavily infected paua exhibited behavioural abnormalities including lethargy, loss of righting reflex, and were easily detached from surfaces. Some heavily infected paua exhibited oedema and pale lesions in the foot and mantle, but no reliable gross signs of disease were noted. Light infections of the haplosporidian were also found in apparently healthy paua from the facility. Histology indicated that the early stages of infection were characterised by small numbers of plasmodia in the connective tissue surrounding the gut, amongst glial cells adjacent to nerves in the mantle and foot and within gill lamellae. In heavy infections, large numbers of small plasmodia (mean size 5.5 x 7 microm in histological sections) were present in the hemolymph, gills, heart, kidneys, mantle, foot, epipodium and connective tissue of the digestive gland. Infections were not transferred horizontally at 14 and 19 degrees C after cohabiting heavily infected paua with uninfected paua for 3 mo in aquaria, or 3 mo after injecting healthy paua with hemolymph containing haplosporidian plasmodia. This may indicate that the prepatent period for disease is longer than 3 mo, that disease is not expressed below 20 degrees C, or that an intermediate host is required for transmission. Spore formation was not observed in juvenile paua but sporocyst-like bodies containing putative spores were observed amongst haplosporidian plasmodia in the right kidney of poorly performing adult paua collected from the wild.     

Infectivity of resting spores of Massospora cicadina (Entomophthorales: Entomophthoraceae), an entomopathogenic fungus of periodical cicadas (Magicicada spp.) (Homoptera: Cicadidae)

Progeny of eastern oyster, Crassostrea virginica, introduced into France in 1992, were reared in IFREMER facilities to test their growth performances. During the summer of 1993, sporadic mass mortalities (80-90%) occurred among C. virginica spat reared in the IFREMER laboratories in La Tremblade (Charente Maritime, France) and Bouin (Vendée, France). Affected oysters presented mantle retraction and deposition of an anomalous conchiolin layer on the inner surface of the shell. The incidence of oysters with gross signs exceeded 80%. No obvious pathogen was identified in soft tissues by histology and transmission electron microscopy (TEM). However, histological examination showed the presence of anomalous basophilic round structures, 0.5-1 microm in diameter, in gill and mantle connective tissues. These extracellular Feulgen-negative structures reacted positively with the von Kossa stain. TEM examination on mantle and gill samples in diseased spat showed that the basophilic bodies consisted of concentric deposits of an amorphous substance interpreted as containing calcium. These observations may indicate that the mineralization process in spat shells was disturbed without exact determination of the cause. Based on the similarities of the gross signs to those reported in juvenile eastern oysters in the United States, we believe that the cause of the mortalities observed in France was probably the Juvenile Oyster Disease. Moreover, we report for the first time the detection of anomalous amorphous structures in gill and mantle connective tissues associated with mortalities and deposition of an anomalous conchioloin layer on the inner shell surface in C. virginica spat.     

Ultrastructural identification of a herpes-like virus infection in common carp Cyprinus carpio in Korea

We report on a herpes-like virus, which was found to be associated with mass mortality of common carp Cyprinus carpio for the first time in Korea in 1998. The external signs of infection in moribund fish were darkened coloration and severe branchial necrosis in the gill. Transmission electron microscopy revealed the presence of herpes-like viruses in spleen tissue. Infected spleen cells showed hypertrophied nuclei and degeneration. Numerous nucleocapsids of about 82 nm in diameter were found within the nucleus and cytoplasm of infected cells, and extracellular enveloped particles were also observed. We conclude that this virus was a likely significant cause of the high mortality of common carp in Korea in 1998.     

Nodavirus infection causes mortalities in hatchery produced larvae of Lates calcarifer: first report from India

Larvae (15 to 21 d post hatch, dph) of the Asian sea bass Lates calcarifer (Bloch) suffered heavy mortalities (60 to 90%) during the hatchery-rearing phase. Darkened and moribund larvae showed no evidence of bacterial or parasitic infections. Tissue sections of brain and spinal cord showed clear necrotic vacuolation. Electron microscopy revealed membrane-bound viral particles in the cytoplasm of the nerve cells. The viral particles measured 28 to 30 nm in diameter. Primer sets, designed for the amplification of the RNA2 segment of the piscine nodavirus coat protein gene, were used in the RT-PCR analysis of moribund larvae of 20 and 21 dph which produced the amplified product of 430 bp. The clinical manifestations, pathology and electron microscopy observations supported by the RT-PCR analysis suggest that the nerve necrosis was due to nodavirus infection in the larvae. This is the first report of piscine nodavirus infection from the Indian sub-continent.     

Virus-like particles associated with mortalities of the carpet-shell clam Ruditapes decussatus

During the late summer and early fall of 1997 and 1998 heavy mortalities were detected in the carpet-shell clam Ruditapes decussatus cultured in Galicia (NW Spain). The prevalences and intensities of the parasites found in the histopathological studies were not high enough to explain the high mortality rates. Unenveloped virus-like particles were detected by transmission electron microscopy in the cytoplasm of the connective tissue cells. They had an icosahedrical-spherical shape with a diameter of 27 to 35 nm. These virus-like particles appeared free in the cytoplasm or associated with endoplasmic reticulum membranes. These characteristics suggest that they belong to the Picornaviridae family.     

Virus-like particles associated with mortalities of the Manila clam Ruditapes philippinarum in England

Mortalities of the Manila clam Ruditapes philippinarum (Adams & Reeve, 1850) were reported in southern England (Kent and Poole Harbour) during late spring of 2008. In response to these reported mortalities, samples were collected from 5 sites across the south coast of England. Clams were sampled for both histology and electron microscopy. Transmission electron microscopy (TEM) revealed unenveloped virus-like particles within the connective tissue of the gills and surrounding the tubules in the digestive gland. The virus-like particles appeared to be free within the cytoplasm or associated with endoplasmic reticulum membranes and cytoplasmic vesicles. Particles were icosahedral in shape, with a diameter of 25 to 30 nm. The location, size and morphology of the virus-like particles suggest that they belong to the Picornaviridae family. This is the first report of this virus infection in wild and farmed R. philippinarum within the UK.     

Histological, ultrastructural, and in situ hybridization study on enlarged cells in grouper Epinephelus hybrids infected by grouper iridovirus in Taiwan (TGIV)

Grouper iridovirus in Taiwan (TGIV) infection in the Epinephelus hybrid is a major problem in the grouper industry. ATPase gene sequences indicate that this virus is closely related to cell hypertrophy iridoviruses. Histologically, the appearance of basophilic or eosinophilic enlarged cells in internal organs is the most characteristic feature of this disease. These cells are acid-phosphatase positive and are able to phagocytose injected carbon particles. In our study, TGIV infection inhibited normal phagocytic ability in these cells in vivo after 4 d post-infection (p.i.) but not before 2 d p.i. Their staining properties and phagocytic ability suggested a monocyte origin of enlarged cells, which appeared in high numbers in the trunk kidney, head kidney, spleen and gill. After infection, the enlarged cells first appeared in the spleen, with an abundance peak at 64 h p.i. (Peak 1); at 120 h p.i., a second peak (Peak 2) occurred in the spleen, head kidney, trunk kidney and gill. Lower numbers of enlarged cells were observed in the liver, muscle, heart, eye, intestine, but no enlarged cells were found in the brain. A TGIV-specific DNA probe labeled most of the basophilic but not eosinophilic enlarged cells. Nuclei of infected cells were labeled during an early stage of the infection; at later stages, both nuclei and cytoplasms were labeled. Ultrastructurally, heterochromatins of the infected cells were marginated or aggregated to one side of the nuclei during the early stages of infection. Damage and rupture of the nuclear membrane started before formation of the viromatrix. Capsids were assembled in ring-shaped or disc-shaped structures. Bullet-shaped electron-dense material was present near the incomplete virus particles, and is speculated to be inserted into the capsids later.     

RT-nested PCR detection of Mourilyan virus in Australian Penaeus monodon and its tissue distribution in healthy and moribund prawns

Mourilyan virus (MoV) is a newly identified virus of Penaeus monodon prawns that is genetically related to the Uukuniemi virus and other phleboviruses of the Bunyaviridae. This paper describes an RT-nested PCR test that can reliably detect between 2 and 6 copies of a synthetic MoV RNA. Total RNA isolated from the lymphoid organ, gills and haemocytes of P. monodon with moderate infections gave comparable amplicon yields in the RT-PCR step of the test. However, in prawns with extremely low-level infections, haemocytes and gill tissue proved slightly more reliable in detecting MoV RNA following nested PCR. The distribution of MoV in tissues of healthy and moribund P. monodon was examined by in situ hybridisation (ISH) using a digoxigenin-labelled DNA probe to a approximately 0.8 kb M RNA segment cDNA insert in clone pMoV4.1. The DNA probe targeted a region in the MoV M RNA segment containing a coding sequence with homology to the C-terminus of the G2 glycoprotein of phleboviruses. In healthy prawns harbouring an unapparent MoV infection, ISH signal primarily occurred in the lymphoid organ, where it was more prominent in hypertrophied cells of 'spheroids' than within cells of normal tubules. ISH signal was also sometimes detected in cells of cuticular epithelium, segmental nerve ganglion and the antennal and tegmental glands. MoV was distributed widely throughout these and other cephalothoracic tissues of mesodermal and ectodermal origin in moribund P. monodon following experimental infection or collected from farm pond edges during disease episodes. Transmission electron microscopy of gill of moribund, captive-reared P. monodon identified spherical (approximately 85 nm diameter) to ovoid MoV particles (approximately 85 x 100 nm) in and around highly necrotic cells in which the nucleus and other organelles had disintegrated. MoV virions co-existed with rod-shaped virions of gill-associated virus and were often seen clustered within cytoplasmic vacuoles or associated with the outer rim of concentric ring-shaped structures comprised of endoplasmic membranes likely to represent degenerated Golgi.     

Characterization of intracytoplasmic prokaryote infections in Dreissena sp. (Bivalvia: Dreissenidae)

This study characterizes intracytoplasmic infections with prokaryote microorganisms in Dreissena sp. (near Dreissena polymorpha) from northeastern Greece and represents the first report of such infections in freshwater bivalves. Light microscope observations of stained tissues revealed basophilic, cytoplasmic inclusion bodies in 87.5% (28/32) of the mussels sectioned. Inclusions in epithelial cells and connective tissues were noted, respectively, in 34.4 and 71.9% of the sample, with 5 mussels (15.6%) having both tissue types infected. Epithelial cell infections were observed in histological sections only in digestive gland tubules and ducts; within tubules, inclusions were present more often in secretory than digestive cells. Connective tissue infections, however, were systemic; among the 32 mussels sectioned, inclusions were found in the gills (65.6%), foot (12.5%), mantle (9.4%), labial palps (6.3%), digestive gland (6.3%), stomach (6.3%), and gonads (3.1%). Cytoplasmic inclusions (maximum dimension, 138 microm) were prominent enough in the gills to be visible in 17.0% of the 247 mussels dissected. Ultrastructurally, prokaryote cells in gill connective tissues were clearly characteristic of Chlamydiales-like organisms, with each intracytoplasmic inclusion containing a loosely packed mixture of elementary, reticulate, intermediate bodies, and blebs. Prokaryote colonies in digestive gland epithelial cells exclusively contained 1 of 4 morphological cell types and were considered Rickettsiales-like. Hexagonal, virus-like particles were present in the cytoplasm of the largest of these Rickettsiales-like prokaryotes. Although host stress was evident from localized cell necrosis and dense hemocyte infiltration, overall infection was fairly benign, with no major, adverse impact on body condition evident among sectioned or dissected mussels. A possible negative effect was partial constriction of gill water tubes, but at the infection intensity observed (typical range 1 to 7 inclusion bodies per section), significant interference with respiration and other metabolic functions of the gills was highly unlikely.     

Further Studies on the Effect of 5-Iododeoxyuridine on Polyoma Virus Multiplication in Mouse Cells

5-Iododeoxyuridine (IUDR) inhibited production of infectious polyoma virus in mouse embryo cells and mouse kidney cells in culture. Deoxythymidine reversed its effect. IUDR did not inactivate infectivity of free virus particles. IUDR did not prevent adsorption and penetration of polyoma virus to cells. The events sensitive to IUDR treatment occurred at around 20 hours after infection. The cytopathic effects of polyoma virus, including emergence of DNA containing-inclusions in the nucleus, were observable in infected cells in which viral replication was completely arrested by IUDR. It was shown by fluorescent antibody technique in infected mouse embryo cells and by complement fixation test in infected mouse kidney cells that IUDR inhibited completely the synthesis of viral antigen. No virus-like particles were demonstrated in the IUDR-treated infected-mouse kidney cells by electron microscope examinations.     

Histopathology of cultured sea bream Sparus aurata infected with sanguinicolid trematodes

The present study is the first report of a sanguinicolid infection affecting sea bream Sparus aurata cultured in net cages in the NE of Spain. The disease was associated with trickling mortalities during the cold season (1999 and 2000). Examination of gill wet mounts of the affected population revealed that sanguinicolid infection was present in 82.6 and 100% of the fish sampled in 1999 and 2000, respectively. Adult flukes, which were located in the kidney, were tentatively identified as members of the family Sanguinicolidae, subfamily Cardicolinae. Eggs and miracidia were found in the gill vascular structures. The inflammatory response triggered by the parasites was moderate and the lesions caused by either eggs and miracidia in the gills or adult flukes in the kidney were not extremely severe, possibly because of the moderate intensity of the parasitosis. Histological observations of sanguinicolid infected sea bream presented here are compared with those reported in other fish species. The role played on sea bream morbility and mortality by other factors (occurrence of a simultaneous moderate monogenean infection, immunological impairement related to low water temperatures) is discussed.     

Characterization of abalone Haliotis tuberculata–Vibrio harveyi interactions in gill primary cultures

The decline of European abalone Haliotis tuberculata populations has been associated with various pathogens including bacteria of the genus Vibrio. Following the summer mortality outbreaks reported in France between 1998 and 2000, Vibrio harveyi strains were isolated from moribund abalones, allowing in vivo and in vitro studies on the interactions between abalone H. tuberculata and V. harveyi. This work reports the development of primary cell cultures from abalone gill tissue, a target tissue for bacterial colonisation, and their use for in vitro study of host cell—V. harveyi interactions. Gill cells originated from four-day-old explant primary cultures were successfully sub-cultured in multi-well plates and maintained in vitro for up to 24 days. Cytological parameters, cell morphology and viability were monitored over time using flow cytometry analysis and semi-quantitative assay (XTT). Then, gill cell cultures were used to investigate in vitro the interactions with V. harveyi. The effects of two bacterial strains were evaluated on gill cells: a pathogenic bacterial strain ORM4 which is responsible for abalone mortalities and LMG7890 which is a non-pathogenic strain. Cellular responses of gill cells exposed to increasing concentrations of bacteria were evaluated by measuring mitochondrial activity (XTT assay) and phenoloxidase activity, an enzyme which is strongly involved in immune response. The ability of gill cells to phagocyte GFP-tagged V. harveyi was evaluated by flow cytometry and gill cells-V. harveyi interactions were characterized using fluorescence microscopy and transmission electron microscopy. During phagocytosis process we evidenced that V. harveyi bacteria induced significant changes in gill cells metabolism and immune response. Together, the results showed that primary cell cultures from abalone gills are suitable for in vitro study of host-pathogen interactions, providing complementary assays to in vivo experiments.     

Assembly of human severe acute respiratory syndrome coronavirus-like particles

Viral particles of human severe acute respiratory syndrome coronavirus (SARS CoV) consist of three virion structural proteins, including spike protein, membrane protein, and envelope protein. In this report, virus-like particles were assembled in insect cells by the co-infection with recombinant baculoviruses, which separately express one of these three virion proteins. We found that the membrane and envelope proteins are sufficient for the efficient formation of virus-like particles and could be visualized by electron microscopy. Sucrose gradient purification followed by Western blot analysis and immunogold labeling showed that the spike protein could be incorporated into the virus like particle also. The construction of engineered virus-like particles bearing resemblance to the authentic one is an important step towards the development of an effective vaccine against infection of SARS CoV.     

Gill lamellar pillar cell necrosis, a new birnavirus disease in Japanese eels.

Since the late 1980s, a birnaviral gill disease has been occurring in Japanese eels Anguilla japonica reared in warmwater ponds in western regions in Japan. Diseased eels mostly displayed marked formations of aneurysmal hematomas within gill lamellae and high mortalities. Histological examination revealed necrosis of pillar cells and subsequent aggregation of erythrocytes inside the lamellar capillaries, and proliferation of interlamellar epithelia onto the lamellae. Gastric gland cells were also necrotized. Electron microscopy revealed birnavirus infection in lamellar pillar cells. The causative birnavirus was isolated and cultured in fish cell lines and was found to be related to an infectious pancreatic necrosis virus (IPNV) Sp serotype by neutralization tests. The viral pathogenicity was confirmed by the results of histopathological examinations and infectivity experiments.     

Histology, ultrastructure, and morphogenesis of a rickettsia-like organism causing disease in the oyster, Crassostrea ariakensis Gould

Moribund specimens of the oyster, Crassostrea ariakensis Gould, aged 2-3 years were collected from Hailing Bay in Yangxi County of Guangdong Province from February to May and November to December in the years 2001, 2002, and 2003. A massive infection by an obligate intracellular prokaryote, specifically a rickettsia-like organism (RLO), was found. Here we report investigations of this RLO in the tissues of the oyster C. ariakensis Gould and describe the histology, ultrastructure, and morphogenesis of this pathogen in C. ariakensis Gould. Light microscopic observations of stained tissues revealed cytoplasmic inclusion bodies typical of prokaryote infection in about 87% (26/30) of the oysters. Most inclusions were observed in epithelial cells and connective tissues of the gill, mantle, and digestive gland of most of the infected oysters. The shape, size, and color of inclusions from different tissues were polymorphic. Electron microscopic examination of digestive gland, gill, and mantle tissues showed that the RLOs were intracytoplasmic. RLOs were often round, dumb-bell-shaped (undergoing binary fission), or occasionally rod-shaped and ranged from approximately 0.58 to 1.20microm in size. The organisms exhibited an ultrastructure characteristic of prokaryotic bacteria-like cells, including a trilaminar cell wall, electron-dense periplasmic ribosome zone, and a DNA nucleoid. Reproductive stages, including transverse binary fission, were observed by TEM. These stages were frequently observed within membrane-bound cytoplasmic vacuoles. Hexagonal phage-like particles in the cytoplasm of RLOs were also observed.     

First report on histology and ultrastructure of an intrahemocytic paramyxean parasite (IPP) from tunicate Halocynthia roretzi in Korea

In 2004, epizootiological studies were conducted on mass mortalities of tunicates Halocynthia roretzi in Goje, Korea. The clinical characteristics of infected H. roretzi were weakness of the tunic, loss of elasticity, and finally death involving a rupture of the tunic. Histological studies revealed severe hemocyte infiltration in the connective tissue surrounding the intestine and mantle of infected H. roretzi. Hypertrophied eosinophilic hemocytes containing several cytoplasmic vacuoles were observed in the connective tissue surrounding the intestine, gill and mantle. Ultrastructural examination revealed the presence of a parasite in the cytoplasm of hemocytes. Secondary cells were observed in the primary cell of the parasite. Spore formation within primary cells suggests that the parasite may be an intrahemocytic paramyxean parasite (IPP) and may cause mass mortality of H. roretzi.     

Pathogenesis of experimentally induced bacterial cold water disease in ayu Plecoglossus altivelis

Ayu Plecoglossus altivelis were experimentally infected with Flavobacterium psychrophilum, which is the causative agent of bacterial cold water disease (CWD). The fish infected by immersion usually died within an hour after they became moribund. The blood volume and haematocrit values of moribund fish were low, while those values of many infected fish that were not moribund were in the range of controls. Most of the affected fish in the immersion-infected groups had ulcerative lesions on their lower jaw. No histological evidence of haemolysis was observed. These results suggest that rapid bleeding occurred through ulcerative lesions, probably causing hypoxia which killed the fish. Ulcerative lesions developed on the dorsal skin when this area had been slightly abraded artificially prior to immersion challenge. Histologically, F. psychrophilum was initially found on the skin that had microscopic injuries, but not on normal skin. The bacterium then entered the dermis and migrated through connective tissues. The lesions subsequently expanded into the underlying musculature through the myosepta, developed necrotic myositis and formed externally open ulcers. Only in later stages of infection did mild lesions develop in the internal organs and the gill, probably caused by the bacterium migrating through blood vessels. This suggests that infection with CWD through the gill or digestive tract is unlikely. Virtually no open lesions were found in ayu challenged by intramuscular injections except at the injection sites. The results suggest that skin injuries are major portals of entry for F. psychrophilum in ayu, and the bacterium has affinity for collagenous connective tissues.     

Autometallographical localisation of Cu and Zn within target cell compartments of winkles following exposure to Cu&Zn mixtures

This investigation attempts to determine the usefulness of autometallography to localise particular metals in certain key tissues of molluscs exposed to metal mixtures. For this purpose, winkles (Littorina littorea) removed from shell were exposed to very high concentrations of either copper (Cu), zinc (Zn) or a mixture of both metals (Cu&Zn) dissolved in sea-water for short periods of time. Protein-bound metals were detected by autometallography as black silver deposits (BSD) on histological sections of gills, foot, mantle, digestive gland/gonad complex, stomach and kidney. Copper was localised within cytoplasmic granules of gill ciliated cells, nephrocytes and stomach epithelial cells as well as within digestive cell lysosomes. Zinc was essentially found in the basal lamina (histological sense) of gill, stomach, kidney and digestive gland epithelia. BSD were also evidenced in cytoplasmic granules of pore cells present in parenchymal connective tissue of mantle, foot, gill, digestive gland and stomach. Copper and zinc concentrations were additionally calculated for the whole soft body as well as for certain organs by atomic absorption spectrophotometry (AAS). According to AAS, a synergistic phenomenon would contribute to increase the rate of Cu and Zn accumulation in presence of each other. However, after exposure to Cu&Zn autometallography did not evidence any synergistic phenomenon, and Cu and Zn were localised in their respective accumulation sites. In conclusion, autometallography might indicate the presence of certain metals in the environment irrespective of factors, such as "metal-metal interaction-like" phenomena, affecting metal concentrations in soft tissues.     

Herpes-like virus infection causing mortality of cultured abalone Haliotis diversicolor supertexta in Taiwan

A herpes-like virus is demonstrated for the first time to be associated with high mortality rates in maricultured abalone Haliotis diversicolor supertexta in Taiwan. Histopathology of moribund abalone indicated that the nerve system was the primary target tissue. The lesions were characterised by tissue necrosis accompanied with infiltration of haemocytes. Electron microscopic examination demonstrated viral particles within the degenerated cerebral ganglion cells. The viruses were hexagonal, approximately 100 nm in diameter and had a single coat. Some viral particles contained a dense nucleoid, while others were empty. The ultrastructure and morphogenesis of the virus particles were consistent with those of the herpesvirus described from the oyster Crassostrea virginica. Experimental infection using supernatant collected from minced visceral organs and muscle of moribund abalone induced 100 % mortality through both intramuscular injection and bath treatments.