''Ranavirus'' is a genus of

viruses 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 ...

, in the family '' Iridoviridae''. There are six other

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

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 within the family '' Iridoviridae'', but ''Ranavirus'' is the only one that includes viruses that are infectious to amphibians and reptiles. Additionally, it is one of the three genera within this family which infect teleost

fish Fish are aquatic, craniate, gill-bearing 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. Approximately 95% of li ...

es, along with ''

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 ...

'' and ''

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 closely ...

''.

Ecological impact

The Ranaviruses, like the Megalocytiviruses, are an

emerging ''Emerging'' is the title of the only album by the Phil Keaggy Band, released in 1977 on NewSong Records. The album's release was delayed due to a shift in record pressing plant priorities following the death of Elvis Presley. The album was re ...

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 Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...

, as epizootics 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 Chytridiomycota are a division of zoosporic organisms in the kingdom Fungi, informally known as chytrids. The name is derived from the Ancient Greek ('), meaning "little pot", describing the structure containing unreleased zoöspores. Chytrid ...

fungus A fungus ( : fungi or funguses) is any member of the 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, separately from th ...

'' Batrachochytrium dendrobatidis'', the causative agent of chytridiomycosis. In the UK, the severity of disease outbreaks is thought to have increased due to climate change.

Etymology

''Rana'' is derived from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

for "frog", reflecting the first isolation of a ''Ranavirus'' in 1960s from the Northern leopard frog (''

Lithobates pipiens ''Lithobates pipiens''Integrated Taxonomic Information System nternet2012''Lithobates pipiens'' pdated 2012 Sept; cited 2012 Dec 26Available from: www.itis.gov/ or ''Rana pipiens'', commonly known as the northern leopard frog, is a species of l ...

'').

Evolution

The ranaviruses appear to have evolved from a fish virus which subsequently infected amphibians and reptiles.

Hosts

Anuran Hosts

Wood frogs ''Lithobates sylvaticus'' or ''Rana sylvatica'', commonly known as the wood frog, is a frog species that has a broad distribution over North America, extending from the boreal forest of the north to the southern Appalachians, with several nota ...

(''Lithobates sylvaticus'') *

American Bullfrog The American bullfrog (''Lithobates catesbeianus''), often simply known as the bullfrog in Canada and the United States, is a large true frog native to eastern North America. It typically inhabits large permanent water bodies such as swamps, po ...

(''Lithobates catesbieanus'') *

Pickerel Frog The pickerel frog (''Lithobates palustris'', formerly ''Rana palustris'') is a small North American frog, characterized by the appearance of seemingly "hand-drawn" squares on its dorsal surface. Distinguishing features The pickerel frog is a m ...

Urodelan Hosts

Reptilian Hosts

*Green pythons (''

Chondropython viridis The green tree python (''Morelia viridis'') is a species of snake in the family Pythonidae. The species is native to New Guinea, some islands in Indonesia, and the Cape York Peninsula in Australia. First described by Hermann Schlegel in 1872, it ...

'') *Burmese star tortoises (''

Geochelone platynota The Burmese star tortoise (''Geochelone platynota'') is a critically endangered tortoise species, native to the dry, deciduous forests of Myanmar (Burma). It is close to extinction in Myanmar, as it is eaten by the native Burmese. Description ...

'') *Leopard tortoise ('' Geochelone pardalis'') *Gopher tortoises ('' Gopherus polyphemus'') *Mountain lizard ('' Lacerta monticola'') *Eastern box turtles ('' Terrapene carolina carolina'') *Florida box turtles ('' Terrapene carolina bauri'') *Western ornate box turtles (''

Terrapene ornata ''Terrapene ornata'' is a species of North American box turtle sometimes referred to as the western box turtle or the ornate box turtle. It is one of two recognized species of box turtle in the United States, having two subspecies. The second rec ...

'') *Spur-thighed tortoises (''

Testudo graeca The Greek tortoise (''Testudo graeca''), also known commonly as the spur-thighed tortoise, is a species of tortoise in the family Testudinidae. ''Testudo graeca'' is one of five species of Mediterranean tortoises (genera '' Testudo'' and '' Ag ...

'')Blahak S., Uhlenbrok C. "Ranavirus infections in European terrestrial tortoises in Germany". ''Proceedings of the 1st International Conference on Reptile and Amphibian Medicine''; Munich, Germany. 4–7 March 2010; pp. 17–23 *Hermann's tortoises (''

Testudo hermanni Hermann's tortoise (''Testudo hermanni'') is a species of tortoise. Two subspecies are known: the western Hermann's tortoise (''T. h. hermanni'' ) and the eastern Hermann's tortoise (''T. h. boettgeri'' ). Sometimes mentioned as a subspecies, ...

'') *Egyptian tortoises (''

Testudo kleinmanni Testudo (which meant "tortoise" in classical Latin) may refer to: * Battering ram, an armored siege engine with metal plating on the top to protect from missiles fired from above * Chevrolet Testudo, a concept car designed and built by Bertone on a ...

'') *Russian tortoises (''

Testudo horsfieldii Testudo (which meant "tortoise" in classical Latin) may refer to: * Battering ram, an armored siege engine with metal plating on the top to protect from missiles fired from above * Chevrolet Testudo, a concept car designed and built by Bertone on a ...

'') *Marginated tortoises (''

Testudo marginata The marginated tortoise (''Testudo marginata'') is a species of tortoise in the family Testudinidae. The species is endemic to Greece, Italy, and the Balkans in Southern Europe. It is the largest European tortoise. The marginated tortoise is he ...

'') *Red-eared sliders (''

Trachemys scripta elegans The red-eared slider or red-eared terrapin (''Trachemys scripta elegans'') is a subspecies of the pond slider (''Trachemys scripta''), a semiaquatic turtle belonging to the family Emydidae. It is the most popular pet turtle in the United States, ...

'') *Common snapping turtles (''

Chelydra serpentina The common snapping turtle (''Chelydra serpentina'') is a species of large freshwater turtle in the family Chelydridae. Its natural range extends from southeastern Canada, southwest to the edge of the Rocky Mountains, as far east as Nova Scotia a ...

'') *Chinese softshell turtles (''

Pelodiscus sinensis The Chinese softshell turtle (''Pelodiscus sinensis'') is a species of softshell turtle that is native to China (Inner Mongolia to Guangxi, including Hong Kong) and Taiwan, with records of escapees—some of which have established introduced po ...

'') *Common flat-tail gecko (''

Uroplatus fimbriatus The common flat-tail gecko (''Uroplatus fimbriatus'') is a gecko endemic to Madagascar. It is found in eastern Madagascar and on the islands Nosy Bohara and Nosy Mangabe. These geckos live in tropical rain forests. They reach a total length of ...

'') *Eastern Fence Lizard (''

Sceloporus undulatus The eastern fence lizard (''Sceloporus undulatus'') is a medium-sized species of lizard in the Family (biology), family Phrynosomatidae. The species is found along forest edges, rock piles, and rotting logs or stumps in the eastern United States. I ...

'')

Taxonomy

The genus contains the following species: *'' Ambystoma tigrinum virus'' *'' Common midwife toad virus'' *'' Epizootic haematopoietic necrosis virus'' *'' European North Atlantic ranavirus'' *'' Frog virus 3'' *'' Santee-Cooper ranavirus'' *'' Singapore grouper iridovirus'' The family ''Iridoviridae'' is divided into seven genera which include ''

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 associate ...

'', '' Iridovirus'', ''

'', ''

'', and ''Ranavirus''. The genus ''Ranavirus '' contains three viruses known to infect amphibians ( Ambystoma tigrinum virus (ATV), Bohle iridovirus (BIV), and frog virus 3).

Structure

Ranaviruses are large

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 ...

DNA viruses measuring approximately 150 nm in diameter with a large single linear dsDNA

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...

of roughly 105 kbpWilliams T, Barbosa-Solomieu V, Chinchar GD (2005). "A decade of advances in iridovirus research" 173-148. ''In'' Maramorosch K, Shatkin A (eds). ''Advances in virus research, Vol. 65'' Academic Press, New York, USA. which codes for around 100 gene products. The main structural component of the

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

capsid is the major capsid protein (MCP).

Replication

Ranaviral replication is well-studied using ''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 (RME), also called clathrin-mediated endocytosis, is a process by which cells absorb metabolites, hormones, proteins – and in some cases viruses – by the inward budding of the plasma membrane (invagination). Thi ...

. Viral particles are uncoated and subsequently move into the

cell nucleus The cell nucleus (pl. nuclei; from Latin or , meaning ''kernel'' or ''seed'') is a membrane-bound organelle found in eukaryotic cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, h ...

, where viral

DNA replication In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritanc ...

begins via a virally encoded

DNA polymerase A DNA polymerase is a member of a family of enzymes that catalyze the synthesis of DNA molecules from nucleoside triphosphates, the molecular precursors of DNA. These enzymes are essential for DNA replication and usually work in groups to create ...

. 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.Chinchar VG, Essbauer S, He JG, Hyatt A, Miyazaki T, Seligy V, Williams T (2005). "Family ''Iridoviridae''" pp. 145–162 in Fauquet CM, Mayo MA, Maniloff J, Desselburger U, Ball LA (eds). ''Virus Taxonomy, Eighth report of the International Committee on Taxonomy of Viruses.'' Academic Press, San Diego, USA. The ''ranavirus'' genome, like other iridoviral genomes is circularly permuted and exhibits terminally redundant DNA. There is evidence that ranavirus infections target macrophages as a mechanism for gaining entry to cells.

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 Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...

necrophagy Scavengers are animals that consume dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a herbivorous feeding be ...

cannibalism Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded in more than 1,500 species. Human cannibalism is well documented, b ...

. Ranaviruses are relatively stable in aquatic environments, persisting several weeks 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 that continent.

Pathogenesis

Synthesis of viral proteins begins within hours of viral entry with

necrosis Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...

apoptosis Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes incl ...

occurring as early as a few hours post-infection.

Seasonal Disease Dynamics

There are several hypothesis for seasonal outbreak patterns observed for Ranavirosis mortality events. Ranaviruses grow ''in vitro'' between 8-30 °C, however for most isolates, warmer temperature result in faster viral replication. A combination of this optimal growth temperature along with shifts in larval amphibian susceptibility result in seasonal outbreak events most often observed during warm summer months. Amphibian mortality events are often observed as larval amphibians reach late Gosner stages approaching

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...

. As larval amphibians reach metamorphic stages of development, their immune system is reorganized prior to the development of adult tissues. During this time period, amphibians are stressed, and their immune systems are down regulated. This decrease in immune function and warmer environmental temperatures allows for greater viral replication and cellular damage to occur. Across 64 mortality events in the United States 54% were found to occur between June-August.

Environmental Persistence

The environmental persistence of Ranaviruses is not understood well, however in realistic environmental conditions the T90 value of an FV3-like virus is 1 day. The duration of persistence is likely affected by temperature and microbial conditions. It is unlikely that ranaviruses persist in the environment outside of host species between outbreak events. Researchers have explored several pathogen reservoirs for the virus which might explain how the virus can persist within an amphibian community. In some amphibian populations, sub-clinically infected individuals may serve as reservoirs for the pathogen. These sub-clinically infected individuals are responsible for reintroduction of the virus to the larval population. With ranaviruses being capable of infected multiple taxa, and with there being differences in susceptibility between taxa, it is likely that sympatric

and

reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...

species may serve as reservoirs for virus as well. Interclass transmission has been proven through the use of mesocosm studies.

Gross pathology

Gross lesions associated with ''Ranavirus'' infection include erythema, generalized swelling, hemorrhage, limb swelling, and swollen and friable livers.

References

External links

ICTV Online (10th) Report: Iridoviridae

Global Ranavirus Consortium

* More information on ''Ranavirus'' and other pathogens impacting amphibian populations, including '' Batrachochytrium dendrobatidis'' and '' Batrachochytrium salamandrivorans'' can be found at the Southeast Partners in Amphibian and Reptile Conservation disease task team web-page

{{Taxonbar, from=Q3418768 Iridoviridae Fish viral diseases Articles containing video clips Virus genera