106) and RNA2 (Mr 0.49 106). Both RNA molecules lack poly(A) tails at their 3
-ends.
|
Type Species |
(SJNNV) |
Virions are nonenveloped, spherical in shape, 25-30 nm in diameter. In contrast with most alphanodaviruses, empty particles have been seen by electron microscopy of some preparations of betanodaviruses (Fig. 3).
Physicochemical and Physical Properties
Virion buoyant density in CsCl of Striped jack nervous necrosis virus (SJNNV) has not been reported but that of Dicentrarchus labrax encephalitis virus (DLEV) is about 1.31-1.36 g/cm3. Virions of DlEV are stable between pH 2-9 and resistant to heating at 56°C for 30 minutes. Infectivity is resistant to extraction of virions with chloroform.
The genome consists of two molecules of positive-sense ssRNA: RNA1 (Mr 1.01 106) and RNA2 (Mr 0.49 106). Both RNA molecules lack poly(A) tails at their 3-ends.
The viral structural proteins consist of two polypeptides of Mr 42 103 and Mr 40 103. It is thought that the latter is a processed form of the former protein, but the relationship between them is not clear.
None reported.
None reported.
Genome Organization and Replication
The betanodaviruses replicate in the cytoplasm. Infected cells contain three ssRNAs: RNA1 (Mr 1.01 106; 3.1 kb); RNA2 (Mr 0.49 106; 1.4 kb) and a subgenomic RNA3 (Mr about 0.13 106; 0.4 kb). RNA3 is not packaged into virions. RNA1 encodes protein 1a (Mr 110 103). RNA2 encodes the CPs: 2a (Mr 42 103) and its putative processed product (Mr 40 103). The protein(s) encoded by RNA3 have not been identified.
Few studies of the antigenic properties of the betanodaviruses have been reported, but SJNNV is antigenically related to both Lates calcarifer encephalitis virus (LcEV) and DLEV.
Nature: All species of the betanodaviruses were isolated from juvenile marine fish, in which they cause a vacuolating encephalopathy and retinopathy associated with behavioral abnormalities and high mortality. These diseases have been detected particularly in commercial fish hatcheries, where they cause significant problems for the marine aquaculture industry.
Laboratory: DlEV replicates in cultured cells from sea bass larvae and from striped snakehead fish. A low level of virus replication was observed in mammalian (COS-1 and HeLa) cells at 28°C.
Antibodies to SJNNV were found in 65% of plasma samples collected from wild and domestic brood stocks of striped jack, suggesting that the virus is very prevalent. Viral antigens were detected in eggs, larvae, and ovaries of hatchery-reared and wild spawner fish, suggesting both horizontal and vertical modes of transmission of the virus.
List of Species Demarcation Criteria in the Genus
The species demarcation criteria applied above for alphanodaviruses also apply to betanodaviruses.
Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, genome sequence accession numbers [ ], and assigned abbreviations ( ) are:
|
Barfin flounder nervous necrosis virus |
RNA2 [D38635] |
(BFNNV) |
|
Dicentrarchus labrax encephalitis virus |
RNA2 [U39876] |
(DlEV) |
|
Japanese flounder nervous necrosis virus |
RNA2 [D38527] |
(JFNNV) |
|
Lates calcarifer encephalitis virus |
(LcEV) | |
|
Redspotted grouper nervous necrosis virus |
RNA2 [D38636] |
(RGNNV) |
|
Striped jack nervous necrosis virus |
RNA2 [D30814] |
(SJNNV) |
|
Tiger puffer nervous necrosis virus |
RNA2 [D38637] |
(TPNNV) |
Tentative Species in the Genus
None reported.
List of Unassigned Viruses in the Family
None reported.
Phylogenetic Relationships within the Family
Within the alphanodaviruses, CP sequences are 44-87% identical to one another at the amino acid level, whereas within the betanodaviruses, CP amino acid sequence identities are 80% or greater. The CP amino acid sequences of the alphanodaviruses are only about 10% identical to those of the betanodaviruses.
Unclassified small RNA viruses with a morphology similar to nodaviruses include Acute bee paralysis virus, Bee slow paralysis virus, Bee virus X, Drosophila A virus and Drosophila P virus, Sacbrood virus, Queensland fruitfly virus, and Triatoma virus. The omegatetraviruses such as Nudaurelia capensis 
virus and Helicoverpa armigera stunt virus contain bipartite ssRNA genomes, but their RNAs are about twice the Mr of nodavirus RNAs and they have no 3-terminal blockage. Tetraviruses also have larger capsids with T = 4 icosahedral symmetry.
Noda is from Nodamura, the name of a village (now a city; Nodashi) in the vicinity of the site where NoV was isolated in Japan. Other nodaviruses are similarly named after the place of isolation or after the host name from which they were isolated.
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