Herpesviruslike viruses

Farley et al. (1972) found a herpes-like infection in the haemocytes of moribund American oysters, C. virginica, held in thermal effluent (28-30°C, within the temperature tolerance range of C. virginica) from a power plant in Maine. Mortalities of 52% were attributed to this infection, which was characterized by Feulgen-positive nuclear inclusions in the haemocytes of all moribund specimens (Fig. 20.1). Similar inclusions were found in wild, apparently healthy, oysters at the site of collection (Farley et al., 1972). Non-enveloped virions, 7090 nm in diameter, were found in the nucelus of infected cells. Enveloped particles, 200-250 nm in diameter, occurred in the cytoplasm. Cowdry type A intranuclear inclusion bodies* (Cowdry, 1934), morphological and nucleic acid characteristics resemble those of other herpes-type viruses (Farley, 1978; Francki et al., 1991).

*Type A nuclear inclusions are amorphous or particulate and condensed in rounded masses, which do not stain like nucleoli. Nuclear infection is total and proceeds to complete degeneration. All basophilic chromatin is marginated. Type B nuclear inclusions are localized in certain areas of the nucleus. The nucleoplasm may not be significantly altered and shows no margination. Type B inclusions do not destroy the nucleus.

Table 20.1. Summary of significant viral infections in shellfish.

Family

Common name (acronym)

Host species

Tissues

Iridovirus

Gill necrosis virus (GNV) = 'maladie des branchies'

Haemocyte infection virus (HIV)

Oyster velar virus (OVV)

Iridovirus-like

Crassostrea angulata; + Crassostrea gigas

C. gigas

Octopus vulgaris

Gills

Haemocytes Velar epithelium Muscle

Birnaviridae

Herpesvirus

Tellina virus (TV) Herpes-type

Herpes-type Herpes-type Herpes-type

Tellina tenuis +

Crassostrea virginica +

Ostrea edulis +

Digestive gland

Haemocytes

?Endothelial Haemocytes Interstitial cells

Herpes-like virus

C. gigas

Gills, mantle and digestive gland

Mature virion size Envelope DNA/

Reference

350-380

Icos.

DNA Comps, 1988

350-380

Icos.

Comps and Bonami, 1977

120-140 59

200-250

122-140

160-180

72-75 or 80

Icos.

Icos.

Icos.

Icos.

Icos, n/a Para-spherical with/ without tail

250-350 nm Icos.

?DNA

Elston and Wilkinson, 1985

Rungger et at., 1971; Farley, 1978

Hill, 1976a; Buchanan 1973 Farley et at., 1972

Hine etal., 1992 Alderman, 1980 Comps and Cochennec, 1993

Renault et at., 1994

Retrovirus Retrovirus-Mke

Reoviridae Reovirus-Mke

Paralysis virus (P-virus)

Mya arenaria

Sepia officinalis Macropipus depurator

Baculoviridae Baculovirus Penaeid shrimps penaei (BP) or Penaeus vannemei singly enveloped nuclear polyhedrosis virus (PvSNPV)

Penaeus Penaeid shrimps monodon type baculovirus (MBV) and plebejus baculovirus (PBV) Baculovirus Penaeus japonicus midgut-gland Penaeus monodon necrosis (BMN) Penaeus orientaiis

Penaeus semisuicatus

Neoplastic haemocytes

Stomach

Haemo-lymph, gills, connective tissue, hepato-

pancreas and midgut

Hepato-pancreas and midgut

Hepato-pancreas and midgut

Hepato-pancreas

-100 (from Icos, figure scale)

75 Icos.

58-65

Icos.

Oprandy and Chang, 1983

Devauchelle and Vago, 1971 Vago, 1966; Bonami et al., 1976

+ with type A pyramidal occlusion body

Couch 1974a, b; Lightner and Redman, 1992

75 X 300

72 x310

+ with type A spherical occlusion body

Lightner and Redman 1981; Lester et al., 1987; Lightner et al., 1992a

Sano et al., 1981

Continued over

Table 20.1. Continued.

Family

Common name (acronym)

Host species

Tissues

Parvovirus

Parvovirus/ Picornavirus

Picornavirus

Yellow-head disease (YHD)

Tau baculovirus

Tau 2

Hepatopan-creatic parvo-like virus (HPV) Infectious hypodermal and haematopoietic necrosis virus (IHHNV) Chesapeake Bay virus (CBV) or blue crab picorna-like virus

P. monodon

Carcinus mediterraneus

Carcinus maenas

Penaeid shrimps

Penaeid shrimps Callinectes sapidus

Haemocytes haemopoietic tissue, gills and cuticle

Hepato-pancreas

Hepato-pancreas

Hepato-pancreas

Hypodermal epithelium of fore- and midgut

Neurons, retina, gills, general epidermis, stomach, hindgut, antennal gland and bladder

PO 00

Mature virion size

Shape

DNA/

RNA Reference

40-50 x 150-200

+ with type B granuloid occlusion body

300-320 bow + tail

Described as identical to tau virus (J. Mari and J.-R. Bonami, unpublished results) 22-24 Icos. - DNA

Boonyaratpalin et al., 1993

Pappalardo and Bonami, 1979

Mari and Bonami, 1986 Lightner and Redman, 1985

17-27

Icos.

Lightner et al., 1983b

Icos, with spikes

Johnson, 1978, 1983

Rhabdo-viridae

Bunyaviridae

Rhabdovirus A (RhVA) = ecdysal gland virus 2 (EGV-2)

Rhabdovirus B (RhVB) = ecdysal gland virus 1 (EGV-1) Crab haemocytopenlc virus (CHV)

S-vlrus

C. sapidus

C. sapidus

C. maenas

M. depurator and possibly C. maenas

(In conjunction with RLV or RhVB or EHV or CBV or BFV)

Mandibular gland, nerve cord, Schwann cells, haemocytes, haemopoletic cells

Mandibular organ decreased blood-clotting and haemocyte count, weakness

25-30 x 100-600

50-70 x 100-179

Haemocytes 55-80

Cardiac cells and endothelial cells of the hepatopancreas blood-vessels

80-130 x 190-230

Bacilli-form and may be flexed

Bacllllform/ ovoid

Spherical ?

?RNA Johnson, 1983

Yudln and Clark, 1978

Bank, 1971, 1974

Ovoid + (with ssRNA Bonami and Vago projections 1971; Bonami et on the a/., 1975; Zerbib outer eta/., 1975;

surface) Bonami, 1976;

Bergoin et at., 1982

80-150 In diameter 50-70 x 240-320

Spherical

Bacllllform

Dis. slg., disease significance; DNA, deoxyribonucleic acid; RNA, ribonucleic acid; ssRNA, single-stranded RNA.

PC CO

Alzheimer Histology Autofluorescence
Fig. 20.1. Intranuclear Herpes sp. infection of Crassostrea virginica haemocytes. h, Herpes inclusion; nc, nuclear chromatin. Original histology slide provided by C.A. Farley. Haematoxylin and eosin (H & E), x 1000.

A herpes-like virus was also found in 7-11-day-old hatchery-reared C. gigas in New Zealand (Hine et al.,1992). Hypertrophied haemocyte nuclei contained non-enveloped virions, 97 ± 4 nm in diameter. Enveloped and tegumented (capsid covering, characteristic of the Herpesviridae, which may or may not be enclosed in an envelope) viral particles, 131 ± 9 nm in diameter, were found in cytoplasmic vacuoles and extracellularly. Nicolas et al. (1992a) and Le Deuff et al. (1994) also found herpes-like infections in hatchery-reared C. gigas larvae in France. Similar infections were found in 3-7-month-old C. gigas on open-water oyster-beds (Renault et al., 1994). As with the other herpes-like infections, mortalities were most severe during warm water temperatures and appear to be linked to overcrowding or other stress-related factors (Buchanan and Richards, 1982). Filtered homogenates of infected larvae were inoculated into cultures of C. gigas larvae and reproduced the mortalities observed under hatchery conditions (Le Deuff et al., 1994). Similar experiments with O. edulis larvae were inconclusive. The virions in C. gigas resemble those described by Hine et al. (1992), measuring approximately 80 nm in diameter (Table 20.1), however, both non-enveloped and enveloped stages were detected in the cytoplasm. Enveloped virions, 125 nm in diameter (size calculated from Renault et al., 1994), have spike-like protrusions on the surface - a characteristic feature of Herpesviridae (Francki et al.,1991) but the nucleic acid constitution of the virus was not determined. In contrast to other herpes-like infections described in bivalves, no haemocyte infiltration was observed in the hatchery-reared C. gigas (Le Deuff et al., 1994; Renault et al., 1994), and it appears likely that these

Hepatopancreatic Parvo Like Virus
Fig. 20.2. (a) Viral gametocytic hypertrophy (VGH) papovavirus-like infection of the gonad of a male Crassostrea virginica. Arrows, hypertrophied cells. H & E, x 160). (b) VGH infection of the gonad of a female Crassostrea virginica. Arrows, hypertrophied cells. H & E, x 160.
Octopus Vulgaris Haemocytes

Fig. 20.3. (and Opposite) (a) VGH infection of the nucleus of a germinal cell of Crassostrea virginica. Note distension of the nuclear membrane and aggregation of mitochondria in the surrounding cytoplasm. Transmission electron microscopy (TEM), x 3000. (b) VGH virogenesis in a germinal cell of Crassostrea virginica. Note virions budding off electron-dense viral stromata (VS) and filamentous forms (arrows). TEM, x 11,000. (c) VGH virions showing icosahedral and subunit morphology. Photograph courtesy of J.-C. Veyrunes and M. Bergoin. Negative stain, TEM, x 63,000.

Fig. 20.3. (and Opposite) (a) VGH infection of the nucleus of a germinal cell of Crassostrea virginica. Note distension of the nuclear membrane and aggregation of mitochondria in the surrounding cytoplasm. Transmission electron microscopy (TEM), x 3000. (b) VGH virogenesis in a germinal cell of Crassostrea virginica. Note virions budding off electron-dense viral stromata (VS) and filamentous forms (arrows). TEM, x 11,000. (c) VGH virions showing icosahedral and subunit morphology. Photograph courtesy of J.-C. Veyrunes and M. Bergoin. Negative stain, TEM, x 63,000.

infections may be related to an earlier record by Alderman (1980), who suggested a viral aetiology for 'summer mortality' in C. gigas from North Wales. This was based on the presence of Cowdry type A inclusions in tissue sections from moribund oysters.

Comps and Cochennec (1993) reported another herpes-like virus in 5-month old European oysters (O. edulis) suffering 90% mortality on oyster-beds in north-eastern France. Infected haemocytes contained Feulgen positive, intranuclear inclusions, comprised of spherical or polygonal particles 80 nm in diameter. Enveloped paraspherical virions, 160-180 nm in diameter, occurred in the cytoplasm. As with infections of C. gigas, mortalities in O. edulis juveniles coincided with warm summer water temperatures.

Gonadal tumour cells in hard-shell clams (M. mercenaria) from Rhode Island have also been associated with nuclear inclusion bodies and peripheral

Parvo Like Virus
Fig. 20.4. Retrovirus-like virions associated with a neoplastic haemocyte of the mussel, Mytilus trossulus. Photograph courtesy of D. Noël. Scale bar = 90 nm.

displacement of host chromatin (Barry and Yevich, 1972). Although described by Farley (1978) and Sindermann (1990) as herpes-like inclusion bodies, ultrastructural investigations by Hesselman et al. (1988) showed a 'haloed granular substance' with no evidence of viral particles. Hesselman et al. (1988) studied different clam populations (and possibly species) from those examined by Barry and Yevich (1972); however, it appears likely that Cowdry-type nuclear inclusions have more than one cause.

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