''Iridoviridae'' is a family of

virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's 1 ...

es with double-stranded DNA genomes. Amphibians, fish, and invertebrates such as arthropods serve as natural hosts. There are currently 22 species in this family, divided among two subfamilies and seven genera.

Nomenclature

The name is derived from

Iris Iris most often refers to: *Iris (anatomy), part of the eye *Iris (mythology), a Greek goddess * ''Iris'' (plant), a genus of flowering plants * Iris (color), an ambiguous color term Iris or IRIS may also refer to: Arts and media Fictional ent ...

, the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

goddess of the

rainbow A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured circular arc. Rainbows c ...

. This name was chosen because of the "rainbow-like" iridescence observed in heavily infected insects and pelleted samples of

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

iridoviruses. It may refer to any member of the ''Iridoviridae'' family or a particular genus within ''Iridoviridae''.

Taxonomy

The following subfamilies and genera are recognized (-''virinae'' denotes subfamily and -''virus'' denotes genus): * '' Alphairdovirinae'' ** ''

Lymphocystivirus ''Lymphocystivirus'' is a genus of viruses, in the family ''Iridoviridae''. Fish serve as natural hosts. There are four species in this genus. Diseases associated with this genus include: tumor-like growths on the skin. Hosts ''Lymphocystivirus ...

'' ** ''

Megalocytivirus ''Megalocytivirus'' is a genus of viruses in the family ''Iridoviridae'' and one of three genera within this family which infect teleost fishes, along with ''Lymphocystivirus'' and ''Ranavirus''. Megalocytiviruses are an emerging group of closel ...

'' ** ''

Ranavirus ''Ranavirus'' is a genus of viruses, in the family ''Iridoviridae''. There are six other genera of viruses within the family ''Iridoviridae'', but ''Ranavirus'' is the only one that includes viruses that are infectious to amphibians and reptile ...

'' * ''

Betairidovirinae ''Betairidovirinae'' is a subfamily of viruses in the family ''Iridoviridae'' that was established in 2016. It is one of two subfamilies within this family, the other being '' Alphairdovirinae''. Most species within the ''Betairidovirinae'' are h ...

'' ** ''

Chloriridovirus ''Chloriridovirus'' is a genus of viruses, in the family ''Iridoviridae''. Diptera with aquatic larval stage, mainly mosquitoes, lepidoptera, and orthoptera insects serve as natural hosts. There are five species in this genus. Diseases associ ...

'' ** '' Daphniairidovirus'' ** '' Decapodiridovirus'' ** ''

Iridovirus ''Iridovirus'' is a genus of viruses in the family '' Iridoviridae''. Insects serve as natural hosts. Currently, only two species are placed in this genus. ''Invertebrate iridescent virus 6'' (IIV-6) was recognised as the type species until su ...

Structure

The

virion A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's ...

s are

icosahedral In geometry, an icosahedron ( or ) is a polyhedron with 20 faces. The name comes and . The plural can be either "icosahedra" () or "icosahedrons". There are infinitely many non- similar shapes of icosahedra, some of them being more symmetrica ...

with

triangulation number A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may ...

(T) = 189–217, 120–350 nm in diameter and made up of three domains: an outer proteinaceous

capsid A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or ma ...

, an intermediate

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

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 The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...

(enveloped viruses) or were arranged in

paracrystalline In materials science, paracrystalline materials are defined as having short- and medium-range ordering in their lattice (similar to the liquid crystal phases) but lacking crystal-like long-range ordering at least in one direction. Origin and ...

arrays within the host cell

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...

and then were released by

cell lysis Lysis ( ) is the breaking down of the membrane of a cell, often by viral, enzymic, or osmotic (that is, "lytic" ) mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a ''lysate''. In molecular bio ...

(unenveloped viruses). The linear genome varies between 150 and 303

kilobase A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DN ...

s 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 ''Lymphocystivirus'', ''Megalocytivirus'', and ''Ranavirus'' have genomes with about 25% of their

cytosine Cytosine () ( symbol C or Cyt) is one of the four nucleobases found in DNA and RNA, along with adenine, guanine, and thymine (uracil in RNA). It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an ...

residues methylated by a virally encoded DNA

methyltransferase Methyltransferases are a large group of enzymes that all methylate their substrates but can be split into several subclasses based on their structural features. The most common class of methyltransferases is class I, all of which contain a Ross ...

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 In molecular biology, RNA polymerase (abbreviated RNAP or RNApol), or more specifically DNA-directed/dependent RNA polymerase (DdRP), is an enzyme that synthesizes RNA from a DNA template. Using the enzyme helicase, RNAP locally opens the ...

II modified by the virus. Meanwhile, host macromolecular synthesis ceases. Parental DNA produces a genome which is then the template for replication in the

. Large

concatemers A concatemer is a long continuous DNA molecule that contains multiple copies of the same DNA sequence linked in series. These polymeric molecules are usually copies of an entire genome linked end to end and separated by ''cos'' sites (a protein bi ...

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.

Pathogenesis

Little is known about the

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

esis of iridoviruses. The pathogenesis is, however, temperature dependent and iridoviruses are thus confined to

poikilothermic A poikilotherm () is an animal whose internal temperature varies considerably. Poikilotherms have to survive and adapt to environmental stress. One of the most important stressors is temperature change, which can lead to alterations in membrane ...

hosts.

Host range

Members of the ''Iridoviridae'' family infect mainly

invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordat ...

, but also some

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

species such as fish, amphibians and reptiles.

References

External links

ICTV Online (10th) Report: ''Iridoviridae''

{{Authority control Virus families