Ranavirus
Encyclopedia
Ranavirus is one of five genera
of virus
es within the family Iridoviridae
, one of the five families of nucleocytoplasmic large DNA viruses
. Ranavirus is the only genus within Iridoviridae that includes viruses that are infectious to amphibians and reptiles, and one of only three genera within this family which infect teleost
fish
es, along with Lymphocystivirus
and Megalocytivirus
. The ranaviruses, like the megalocytiviruses, are an emerging group of closely related dsDNA
viruses which cause systemic infections
in a wide variety of wild and cultured fresh and saltwater fishes. As with megalocytiviruses, Ranavirus outbreaks are therefore of considerable economic importance in aquaculture
, as epizootic
s can result in moderate fish loss or mass mortality events of cultured fishes. Unlike megalocytiviruses, however, Ranavirus infections in amphibians have been implicated as a contributing factor in the global decline of amphibian populations. The impact of ranaviruses on amphibian populations has been compared to the chytrid fungus
Batrachochytrium dendrobatidis
, the causative agent of chytridomycosis.
for "frog", reflecting the first isolation of a Ranavirus in 1960s
from Lithobates pipiens, formerly Rana pipiens.
of roughly 105 kbp which codes for around 100 gene products. The main structural component of the protein
capsid
is the major capsid protein (MCP).
for the genus, frog virus 3 (FV3). Replication of FV3 occurs between 12 and 32 degrees Celsius. Ranaviruses enter the host cell by receptor-mediated endocytosis
. Viral particles are uncoated and subsequently move into the cell nucleus
, where viral DNA replication
begins via a virally encoded DNA polymerase
. Viral DNA then abandons the cell nucleus and begins the second stage of DNA replication in the cytoplasm, ultimately forming DNA concatemers. The viral DNA is then packaged via a headful mechanism into infectious virions. The ranavirus genome, like other iridoviral genomes is circularly permuted and exhibits terminally redundant DNA
.
or apoptosis
occurring as early as a few hours post-infection.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
es within the family Iridoviridae
Iridoviridae
Iridoviridae are a family of viruses with double stranded DNA genomes. 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.-Taxonomy:The...
, one of the five families of nucleocytoplasmic large DNA viruses
Nucleocytoplasmic large DNA viruses
The nucleocytoplasmic large DNA viruses or NCLDV refers to a number of families of large eukaryotic DNA viruses:# Asfarviridae# Iridoviridae# Marseilleviridae# Megaviridae# Mimiviridae# Phycodnaviridae# Poxviridae...
. Ranavirus is the only genus within Iridoviridae that includes viruses that are infectious to amphibians and reptiles, and one of only three genera within this family which infect teleost
Teleostei
Teleostei is one of three infraclasses in class Actinopterygii, the ray-finned fishes. This diverse group, which arose in the Triassic period, includes 20,000 extant species in about 40 orders; most living fishes are members of this group...
fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
es, along with Lymphocystivirus
Lymphocystivirus
Lymphocystivirus is one of five genera of viruses within the viral family Iridoviridae, and one of three genera within this family which infect teleost fishes, along with Megalocytivirus and Ranavirus...
and Megalocytivirus
Megalocytivirus
Megalocytivirus is one of five genera of viruses within the family Iridoviridae and one of three genera within this family which infect teleost fishes, along with Lymphocystivirus and Ranavirus. The megalocytiviruses are an emerging group of closely related dsDNA viruses which cause systemic...
. The ranaviruses, like the megalocytiviruses, are an emerging group of closely related dsDNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
viruses which cause systemic infections
Systemic disease
Life-threatening disease redirects here.A systemic disease is one that affects a number of organs and tissues, or affects the body as a whole. Although most medical conditions will eventually involve multiple organs in advanced stage Life-threatening disease redirects here.A systemic disease is one...
in a wide variety of wild and cultured fresh and saltwater fishes. As with megalocytiviruses, Ranavirus outbreaks are therefore of considerable economic importance in aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
, as epizootic
Epizootic
In epizoology, an epizootic is a disease that appears as new cases in a given animal population, during a given period, at a rate that substantially exceeds what is "expected" based on recent experience . Epidemic is the analogous term applied to human populations...
s can result in moderate fish loss or mass mortality events of cultured fishes. Unlike megalocytiviruses, however, Ranavirus infections in amphibians have been implicated as a contributing factor in the global decline of amphibian populations. The impact of ranaviruses on amphibian populations has been compared to the chytrid fungus
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
Batrachochytrium dendrobatidis
Batrachochytrium dendrobatidis
Batrachochytrium dendrobatidis is a chytrid fungus that causes the disease chytridiomycosis. In the decade after it was first discovered in amphibians in 1998, the disease devastated amphibian populations around the world, in a global decline towards multiple extinctions, part of the Holocene...
, the causative agent of chytridomycosis.
Etymology
Rana is derived from the LatinLatin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
for "frog", reflecting the first isolation of a Ranavirus in 1960s
1960s
The 1960s was the decade that started on January 1, 1960, and ended on December 31, 1969. It was the seventh decade of the 20th century.The 1960s term also refers to an era more often called The Sixties, denoting the complex of inter-related cultural and political trends across the globe...
from Lithobates pipiens, formerly Rana pipiens.
Taxonomy
The family Iridoviridae is divided into five genera which include Chloriridovirus, Iridovirus, Lymphocystivirus, Megalocytivirus, and Ranavirus. The genus Ranavirus is composed of at least 6 recognized viral species, 3 of which are known to infect amphibians (Ambystoma tigrinum virus (ATV), Bohle iridovirus (BIV), and frog virus 3).Structure
Ranaviruses are large icosahedral DNA viruses measuring approximately 150 nm in diameter with a large single linear dsDNA genomeGenome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
of roughly 105 kbp which codes for around 100 gene products. The main structural component of the protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
capsid
Capsid
A capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic...
is the major capsid protein (MCP).
Replication
Ranaviral replication is well-studied using the type speciesType species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
for the genus, frog virus 3 (FV3). Replication of FV3 occurs between 12 and 32 degrees Celsius. Ranaviruses enter the host cell by receptor-mediated endocytosis
Receptor-mediated endocytosis
Receptor-mediated endocytosis , also called clathrin-dependent endocytosis, is a process by which cells internalize molecules by the inward budding of plasma membrane vesicles containing proteins with receptor sites specific to the molecules being internalized.-Process:After the binding of a...
. Viral particles are uncoated and subsequently move into the cell nucleus
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
, where viral DNA replication
DNA replication
DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...
begins via a virally encoded DNA polymerase
DNA polymerase
A DNA polymerase is an enzyme that helps catalyze in the polymerization of deoxyribonucleotides into a DNA strand. DNA polymerases are best known for their feedback role in DNA replication, in which the polymerase "reads" an intact DNA strand as a template and uses it to synthesize the new strand....
. Viral DNA then abandons the cell nucleus and begins the second stage of DNA replication in the cytoplasm, ultimately forming DNA concatemers. The viral DNA is then packaged via a headful mechanism into infectious virions. The ranavirus genome, like other iridoviral genomes is circularly permuted and exhibits terminally redundant DNA
Terminally redundant DNA
Terminally redundant DNA is DNA that contains repeated sequences at each end called terminal repeats. These ends are used to join the ends of the linear DNA to form a cyclic DNA....
.
Transmission
Transmission of ranaviruses is thought to occur by multiple routes, including contaminated soil, direct contact, waterborne exposure, and ingestion of infected tissues during predation, necrophagy or cannibalism. Ranaviruses are relatively stable in aquatic environments, persisting several week or longer outside a host organism.Epizoology
Amphibian mass mortality events due to Ranavirus have been reported in Asia, Europe, North America, and South America. Ranaviruses have been isolated from wild populations of amphibians in Australia, but have not been associated with mass mortality on this continent.Pathogenesis
Synthesis of viral proteins begins within hours of viral entry with necrosisNecrosis
Necrosis is the premature death of cells in living tissue. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma. This is in contrast to apoptosis, which is a naturally occurring cause of cellular death...
or apoptosis
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...
occurring as early as a few hours post-infection.