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Type Species |
(IIV-6) |
Particle diameter is 120-130 nm in ultrathin section. IIV-1 and Invertebrate iridescent virus 2 (IIV-2) are assumed to comprise 1472 capsomers arranged in 20 trimers and 12 pentamers.
Physicochemical and Physical Properties
Virions have an Mr of approximately 1.28 106, a buoyant density of 1.30-1.33 g/cm3 in CsCl and a sedimentation coefficient S20,w of 2200-2250S.
Genome sizes vary from 140-210 kbp although the terminal redundancy of the genome means that each virion DNA molecule will be somewhat longer than the unit genome length. The GC content is typically 29-32%.
Two dimensional SDS-PAGE of Invertebrate iridescent virus 6 (IIV-6) has revealed the presence of 35 polypeptides ranging from Mr 11 to 300 103. The capsid protein exists in two forms, a 50 103 entity located on the exterior surface of the capsid and as a disulphide-linked trimer of identical Mr 50 103 subunits forming a protein of Mr 150 103 located on the interior of the capsid.
The internal lipid layer is believed to be important in the stability of these viruses in aquatic environments. Treatments with chloroform reduces the infectivity and persistence of IIV-6 and Anticarsia gemmatalis iridescent virus (AGIV) whereas IIV-2 has been reported as insensitive to treatment with ether or chloroform.
Genetic studies have indicated the presence of discrete complexes of inter-related viruses within this genus: one large complex containing 10 tentative species, and two smaller complexes. Serological relationships follow a similar pattern.
Reported from a wide range of arthropods, particularly insects in aquatic or damp habitats. Patent infections of hosts and purified pellets of virus often show violet, blue or turquoise iridescence, although inapparent non-lethal infections may be common in certain hosts. No evidence exists for transovarial transmission and where horizontal transmission has been demonstrated, it is usually by cannibalism or predation of infected invertebrate hosts. Many members of the genus can replicate in a large diversity of insect hosts following injection of inoculum. The host range in nature appears to vary but there is evidence of natural transmission across insect orders and even phyla for some viruses. Invertebrate iridescent viruses have a global distribution.
List of Species Demarcation Criteria in the Genus
The following species defining characteristics and associated limits are preliminary in nature. The following definitions assume that all material being compared has been grown under near identical conditions and prepared for examination following identical protocols. It is recommended that both recognized virus species be included in all characterization studies of novel isolates.
1. |
Sequence of the major capsid protein or partial amino acid sequence. Distinct species should exhibit not more than 90% amino acid identity for the complete protein sequence. PCR primers have been designed for conserved regions of this gene (Stohwasser et al. 1993; Webby and Kalmakoff, 1998). |
2. |
Sequence of a limited number of other proteins is known for IIV-1 (96 103 protein) and IIV-6 (various including putative DNA dependent RNA polymerase subunit; helicase; iap homologue; type 6 zinc finger protein), although these have not been used for species differentiation and quantitative limits to similarity have yet to be established. |
3. |
DNA-DNA dot-blot hybridization values should be less than 50% for distinct species under conditions given elsewhere (Williams and Cory, 1994). DNA-DNA reassociation in solution may be more accurate (Johnson, 1994) but has not yet been used for species comparisons of iridoviruses. |
4. |
Using a selection of not less than 4 restriction endonucleases (rare and frequent cutting) distinct species should show completely distinct restriction endonuclease profiles. |
5. |
Antisera from strains of a species should exhibit high levels of cross reactivity. Within and among species comparisons by Western blot analysis using antibodies raised against disrupted virions is the preferred method. Comparisons should be performed simultaneously wherever possible and reference species should be included in each determination. |
The major structural protein of IIV-1 shows 66.4% amino acid identity to that of IIV-6 and approximately 50% or lower amino acid sequence identity to iridoviruses in other genera. Less than 1% DNA-DNA hybridization for genomic DNA was detected by dot-blot method between IIV-1 and IIV-6 (stringency: 26% mismatch). Restriction endonuclease profiles (HindII, EcoRI, SalI) showed a coefficient of similarity of less than 66% between IIV-1 and IIV-6. These species did not share common antigens when tested by tube precipitation, infectivity neutralization, reversed single radical immunodiffusion or enzyme-linked immunosorbant assay (ELISA). It appears that genome size and protein size differences are not useful to differentiate these species; genome sizes can be highly variable among strains of a species whereas the size of the major capsid protein is well conserved among species and shows little variation in size. Little is known about the usefulness of other proteins as species demarcation criteria in the genus.
Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names and assigned abbreviations ( ) are:
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Invertebrate iridescent virus 1 |
[M33542, M62953] |
(IIV-1) |
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(Tipula iridescent virus) |
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Invertebrate iridescent virus 6 |
[AF003534; M99395] |
(IIV-6) |
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(Chilo iridescent virus) |
Tentative Species in the Genus
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Anticarsia gemmatalis iridescent virus |
[AF042343] |
(AGIV) |
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Invertebrate iridescent virus 2 |
[AF042335] |
(IIV-2) |
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(Sericesthis iridescent virus) |
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Invertebrate iridescent virus 9 |
[AF025774] |
(IIV-9) |
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(Invertebrate iridescent virus 10) |
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(Invertebrate iridescent virus 18) |
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(Opogonia iridescent virus) |
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(Wiseana iridescent virus) |
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(Witlesia iridescent virus) |
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Invertebrate iridescent virus 16 |
[AF025775] |
(IIV-16) |
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(Costelytra zealandica iridescent virus) |
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Invertebrate iridescent virus 21 |
(IIV-21) | |
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(Heliothis armigera iridescent virus) |
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(Insect iridescent virus 28) |
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(Lethocerus columbinae iridescent virus) |
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Invertebrate iridescent virus 22 |
[AF042341; M32799] |
(IIV-22) |
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(Simulium sp. iridescent virus) |
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Invertebrate iridescent virus 23 |
[AF042342] |
(IIV-23) |
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(Black beetle iridescent virus) |
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(Heteronychus arator iridescent virus) |
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Invertebrate iridescent virus 24 |
[AF042340] |
(IIV-24) |
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(Apis iridescent virus) |
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(Bee iridescent virus) |
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Invertebrate iridescent virus 29 |
[AF042339] |
(IIV-29) |
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(Tenebrio molitor iridescent virus) |
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Invertebrate iridescent virus 30 |
[AF042336] |
(IIV-30) |
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(Heliothis/Helicoverpa zea iridescent virus) |
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Invertebrate iridescent virus 31 |
[AF042337] |
(IIV-31) |
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(Armadillidium vulgare iridescent virus) |
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(Isopod iridescent virus) |
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(Porcellio dilatatus iridescent virus) |
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(Invertebrate iridescent virus 32) |
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