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Family	00.082.  Ascoviridae
	Taxonomic Structure of the Family
	Family         00.082. Ascoviridae Genus                      00.082.0.01. Ascovirus

List of Species Demarcation Criteria in the Genus

Ascoviruses can have broad host ranges among the larvae of lepidopteran species, and the fat body tissue is a major site of replication for most species. In addition, the virions of most isolates are similar in size and shape. The above characters are therefore used in combination to distinguish existing and new ascovirus species from one another. Hybridization studies have proven particularly useful, and when combined with RFLPs can also be used to distinguish variants within a species.

For example, SfAV-1a DNA does not hybridize with HvAV-3a, TnAV-2a, or DpAV-4a DNAs under conditions of low stringency, nor does DpAV-4a hybridize with the DNA of the other species. TnAV-2a DNA does hybridize to some extent with HvAV-3a DNA, but not as strongly as it does with homologous DNA. In addition, the TnAV-2a replicates in a range of larval tissues including the fat body, tracheal matrix and epidermis, but SfAV-1a and HvAV-3a appear to replicate, respectively, only or primarily in the fat body tissue of most hosts. DpAV-4a replicates primarily in the pupal stage, where the primary tissues attacked are the fat body and midgut. SfAV-1a virions are bacilliform and are occluded in vesiculate occlusion bodies, whereas TnAV-2a virions are allantoid and are not occluded in occlusion bodies. HvAV-3a virions vary from allantoid to bacilliform, and are not occluded in occlusion bodies. The DpAV genome is carried as free circular DNA in nuclei of its wasp host, Diadromus pulchellus, and is transmitted vertically to wasp progeny. However, vertical transmission in wasp vectors is not known to occur with the other ascoviruses.

When the genome of a new isolate cross-hybridizes with that of an existing species member, RFLPs can be used to distinguish variants. Numerous ascovirus isolates, for example, have been obtained from larvae of different noctuid species, including Heliothis virescens, Helicoverpa zea, Autographa precationis and Spodoptera exigua in the U.S., as well as from Helicoverpa and Spodoptera species in Australia and Indonesia. The DNA of many of these isolates shows strong reciprocal hybridization with HvAV-3a DNA under conditions of high stringency. RFLP profiles of these isolates, however, often show variations from HvAv-3a that range from minor to major. Because these isolates crosshybridize strongly with HvAV-3a, they are considered variants of this viral species. Moreover, experimentally these isolates have been shown to have host ranges that overlap with HvAV-3a, providing additional evidence that they are variants of the same species. A similar situation occurs with isolates of TnAv-2a.

List of Species in the Genus

The ICTVdB virus code and the viruses. Official virus species names are in italics. Tentative virus species names, alternative names ( ), isolates, strains, serotypes, subspecies, or rejected names are not italicized.
 
Virus codes, virus names, genome sequence accession numbers [ ] and assigned abbreviations ( ), are:

Species, their serotypes, strains and isolates

Tentative Species in the Genus

List of Unassigned Viruses in the Family

None reported.

Similarity with other Taxa

The virions of ascoviruses resemble the particles produced by ichnoviruses of the viral family Polydnaviridae. Though the virions of members of the family Ascoviridae differ considerably from viruses of the family Iridoviridae, evidence is mounting that the ascoviruses and iridoviruses shared a common ancestor. In fact, phylogenetic analyses of several major proteins found in most enveloped dsDNA viruses provide strong evidence that ascoviruses evolved from iridoviruses, despite the marked differences in the morphology of the virions characteristic of these two families, and differences in their cytopathology. The modifications in virion morphology may have evolved as a result of the transmission of the virions on the ovipositors of parasitic wasps. Similarities in virion structure may also indicate that ichnoviruses evolved from ascoviruses.

Derivation of Names

Asco: From the Greek for "Sac;" referring to the virion-containing vesicles produced by cleavage of host cells, which are characteristic for all known viruses of this family.

References

Collated from VIIIth ICTV Report

Contributed by

Federici, B.A., Bigot, Y., Granados, R.R., Hamm, J.J., Miller, L.K., Newton, L, Stasiak, K. and Vlak, J.M.

Version 4 is based on Virus Taxonomy, Classification and Nomenclature of Viruses, 8th ICTV Report of the International Committee on Taxonomy of Viruses. Fauquet, CM, Mayo, MA, Maniloff, J, Desselberger, U, and Ball, LA (EDS) (2005) Elsevier/Academic Press, pp. 1259.

Additional References

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