Iridoviridae

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Iridoviridae
Virus classification Red Pencil Icon.png
(unranked): Virus
Phylum: incertae sedis
Class: incertae sedis
Order: incertae sedis
Family:Iridoviridae
Genera

Iridoviridae is a family of viruses with double-stranded DNA genomes. [1] Amphibia, fish, invertebrates, lepidoptera, and orthoptera insects serve as natural hosts. There are currently 12 species in this family, divided among two subfamilies and 5 genera. [1] [2]

Virus Type of non-cellular infectious agent

A virus is a small infectious agent that replicates only inside the living cells of an organism. Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea.

DNA Molecule that encodes the genetic instructions used in the development and functioning of all known organisms and many viruses

Deoxyribonucleic acid is a molecule composed of two chains that coil around each other to form a double helix carrying genetic instructions for the development, functioning, growth and reproduction of all known organisms and many viruses. DNA and ribonucleic acid (RNA) are nucleic acids; alongside proteins, lipids and complex carbohydrates (polysaccharides), nucleic acids are one of the four major types of macromolecules that are essential for all known forms of life.

Lepidoptera Order of insects including moths and butterflies

Lepidoptera is an order of insects that includes butterflies and moths. About 180,000 species of the Lepidoptera are described, in 126 families and 46 superfamilies, 10 per cent of the total described species of living organisms. It is one of the most widespread and widely recognizable insect orders in the world. The Lepidoptera show many variations of the basic body structure that have evolved to gain advantages in lifestyle and distribution. Recent estimates suggest the order may have more species than earlier thought, and is among the four most speciose orders, along with the Hymenoptera, Diptera, and Coleoptera.

Contents

Nomenclature

The name is derived from Iris the Greek goddess of the rainbow. This name was chosen because of the "rainbow-like" iridescence observed in heavily infected insects and pelleted samples of invertebrate iridoviruses. It may refer to any member of the Iridoviridae family or a particular genus within Iridoviridae.

Iris (mythology) Greek goddess of the rainbow

In Greek mythology, Iris is the personification and goddess of the rainbow and messenger of the gods.

Greece republic in Southeast Europe

Greece, officially the Hellenic Republic, also known as Hellas, is a country located in Southern and Southeast Europe. Its population is approximately 10.7 million as of 2018; Athens is the nation's capital and largest city, followed by Thessaloniki.

Goddess feminine or female deity

A goddess is a female deity. Goddesses have been linked with virtues such as beauty, love, motherhood and fertility. They have also been associated with ideas such as war, creation, and death.

Taxonomy

Group: dsDNA

[1]

Other species include the shrimp haemocyte iridescent virus.

Structure

The virions are icosahedral with triangulation number (T) = 189–217, 120–350 nm in diameter and made up of three domains: an outer proteinaceous capsid, an intermediate lipid membrane, and a central core containing DNA-protein complexes. Some of the viruses also have an outer envelope. The presence or absence of an envelope depends on whether they budded from the cell membrane (enveloped viruses) or were arranged in paracrystalline arrays within the host cell cytoplasm and then were released by cell lysis (unenveloped viruses).

The linear genome varies between 150 and 303 kilobases in length. It contains terminal and redundant sequences and is circularly permuted.

Members of this family differ in their degree of genome methylation. The genera Chloriridovirus and Iridovirus lack a highly methylated genome. Members of the Lymphocystivirus, Megalocytivirus, and Ranavirus genera have genomes with about 25% of their cytosine residues methylated by a virally encoded DNA methyltransferase.

GenusStructureSymmetryCapsidGenomic arrangementGenomic segmentation
LymphocystivirusPolyhedralT=189-217LinearMonopartite
MegalocytivirusPolyhedralT=189-217LinearMonopartite
RanavirusPolyhedralT=133 or 147LinearMonopartite
IridovirusPolyhedralT=147LinearMonopartite
ChloriridovirusPolyhedralT=189-217LinearMonopartite

Gene expression

Similar to the herpes viruses, transcription occurs in three stages: immediate-early, delayed-early, and late. Positive induction and negative feedback mechanisms exist in each stage, mediated by products of the other stages.

Replication

Virus particles enter the cell and uncoating occurs. The viral DNA is transported to the host cell nucleus, where it is transcribed by host RNA polymerase II modified by the virus. Meanwhile, host macromolecular synthesis is stopped.

Parental DNA produces a genome which is then the template for replication in the cytoplasm. Large concatemers of viral DNA are formed by recombination in the cytoplasm. Packaging of the new genomes into virions occurs in the cytoplasm and the virus is released either by budding from the cell membrane or cell lysis.

GenusHost detailsTissue tropismEntry detailsRelease detailsReplication siteAssembly siteTransmission
Lymphocystivirus FishNoneCell receptor endocytosisLysis; buddingNucleusCytoplasmUnknown
Megalocytivirus FishNoneCell receptor endocytosisLysis; buddingNucleusCytoplasmUnknown
Ranavirus Frogs; snakesNoneCell receptor endocytosisLysis; buddingNucleusCytoplasmContact
Iridovirus InsectsNoneCell receptor endocytosisLysis; buddingNucleusCytoplasmContact
Chloriridovirus Diptera with aquatic larval stage, mainly mosquitoesNoneCell receptor endocytosisBuddingNucleusCytoplasmUnknown

Pathogenesis

Little is known about the pathogenesis of iridoviruses. The pathogenesis is, however, temperature dependent and iridoviruses are thus confined to poikilothermic hosts.

Host range

Members of the Iridoviridae family infect mainly invertebrates, but also some vertebrate species such as fish, amphibians and reptiles.

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References

  1. 1 2 3 "Iridoviridae". ICTV Online (10th) Report.
  2. "Viral Zone". ExPASy. Retrieved 15 June 2015.

MicrobiologyBytes: Iridoviruses, archived from the original on February 24, 2007, retrieved 2007-03-06

Viral Bioinformatics Resource Center & Viral Bioinformatics – Canada, University of Victoria, archived from the original on August 17, 2007, retrieved 2007-03-06