Snakehead rhabdovirus
Encyclopedia
Snakehead rhabdovirus is a Novirhabdovirus
that affects various species warm water wild and pond-cultured fish in Southeast Asia
, including snakehead
species for which it is named.
and 1980s
to search for infectious agents that cause or contribute to a severe ulcerative disease, known as epizootic ulcerative syndrome
(EUS), which causes high mortalities among a variety of fish species in Asia
and the Pacific region. SNRV was isolated by virologist W. Wattanavijarn from a snakehead murrel, Channa striata
(formerly Ophicepahalus striatus), a species of snakehead
fish, which exhibited signs of epizootic ulcerative syndrome following an outbreak of this syndrome in Thailand
. The new viral isolate was identified as a rhabdovirus based on images and measurements taken via transmission electron microscopy
and biochemical test results. Plaque neutralization tests and immunofluorescence
tests demonstrated that the new isolate was serologically unrelated to several other fish rhabdoviruses, including anquilla rhabdovirus (EVX), infectious hematopoietic necrosis virus
(IHNV), pike fry rhabdovirus (PFRV), spring viremia of carp virus (SVCV), and viral hemorrhagic septicemia
virus (VHSV). Subsequent infection studies exposing healthy snakehead murrels from a susceptible population to SHNV did not develop clinical signs associated with EUS, suggesting that SHRV does not play a significant role in EUS.
(G) and the polymerase
(L) genes, and contains a single open reading frame
(ORF), which is 335 nucleotide
s in length. It is called the "nonvirion" gene because no corresponding protein is present in the virion. Although the NV genes of novirhabdoviruses are similar in size, including approximately 110-122 codons, little sequence homology
is evident.
Coding sequences of its glycoprotein (G) genes were found to be similar to the three other presently-classified novirhabdoviruses, VHSV, IHNV, and Hirame rhabdovirus (HIRRV), with between 36% and 47% amino acid identity.
is a non-segmented, negative sense RNA genome that is approximately 11,550 nucleotides in length, with six ORFs, including the matrix (M) gene, the nonvirion (NV) gene, the nucleoprotein
(N) gene, the phosphoprotein
(P) gene, the polymerase
(large protein, L) gene, and the viral glycoprotein gene (G), arranged in the following order: 3'-N-P-M-G-NV-L-5'.
, although the optimal temperature range for viral replication is between 28°C and 31°C.
(pH = 3), chloroform
(50%), and heat
(56°C). SHRV in distilled water
can be completely inactivated by less than five minutes of exposure to 12.5 ppm chlorine
, 50 ppm iodine
, or a 1:2000 dilution of peroxygen disinfectant.
Exposure of infective virions in cell culture material to 2% formalin reduced infectivity by 99.9% after 5 minutes, and completely after 30 minutes. However, exposure of infectious cell culture material to 0.025% formalin for 60 minutes caused only a negligible reduction in infectivity, and more than 50 ppm chlorine was needed to inactivate the virus Also in cell culture fluids, exposure to 500 ppm iodine for 30 minutes did not reduce infectivity. The virus does not lose infectivity when exposed in cell culture fluids to malachite green
for 6 hours at 5 ppm.
of infection
.
Subsequent experimental infections exposed zebrafish embryos, juveniles, and adults to SHRV by immersion and/or intraperitoneal (IP) injection
. Whereas embryos and larvae were susceptible to infection by immersion, adult zebrafish were only susceptible to infection by IP injection. Histopathology
of infected embryos and juvenile fish revealed vascular monocyte
accumulation, accumulation of cellular debris in the gas bladder
, necrosis
of hepatocytes, and necrosis of pharyngeal epithelial cells. SHRV induced interferon
(IFN) and orthomyxovirus resistance (Mx) gene expression in zebrafish at levels dependent on route of inoculation and fish age.
Novirhabdovirus
Novirhabdovirus is one of the genera of Rhabdoviridae, along with Vesiculovirus, known to infect aquatic hosts. They can be transmitted from fish to fish, by waterborne virus, as well as through contaminated eggs. Replication and thermal inactivation temperatures are generally lower than for other...
that affects various species warm water wild and pond-cultured fish in Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...
, including snakehead
Channidae
The Snakeheads are members of the freshwater perciform fish family Channidae, native to Africa and Asia. These elongated predatory fish are distinguished by a long dorsal fin, large mouth and shiny teeth. They breathe air with a suprabranchial organ, a primitive form of a labyrinth organ...
species for which it is named.
Isolation
Investigations were conducted in the 1970s1970s
File:1970s decade montage.png|From left, clockwise: US President Richard Nixon doing the V for Victory sign after his resignation from office after the Watergate scandal in 1974; Refugees aboard a US naval boat after the Fall of Saigon, leading to the end of the Vietnam War in 1975; The 1973 oil...
and 1980s
1980s
File:1980s decade montage.png|thumb|400px|From left, clockwise: The first Space Shuttle, Columbia, lifted off in 1981; American President Ronald Reagan and Soviet leader Mikhail Gorbachev eased tensions between the two superpowers, leading to the end of the Cold War; The Fall of the Berlin Wall in...
to search for infectious agents that cause or contribute to a severe ulcerative disease, known as epizootic ulcerative syndrome
Epizootic ulcerative syndrome
Epizootic ulcerative syndrome is a disease caused by the fungus, Aphanomyces invadans. It infects many freshwater and brackish fish species in the Asia-Pacific region and Australia. The disease is most commonly seen when there are low temperature and heavy rainfall in tropical and sub-tropical...
(EUS), which causes high mortalities among a variety of fish species in Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
and the Pacific region. SNRV was isolated by virologist W. Wattanavijarn from a snakehead murrel, Channa striata
Channa striata
The snakehead murrel, Channa striata, is a species of snakehead fish. It is also known as the common snakehead, chevron snakehead, striped snakehead, haloan, aruan, haruan and dalag...
(formerly Ophicepahalus striatus), a species of snakehead
Channidae
The Snakeheads are members of the freshwater perciform fish family Channidae, native to Africa and Asia. These elongated predatory fish are distinguished by a long dorsal fin, large mouth and shiny teeth. They breathe air with a suprabranchial organ, a primitive form of a labyrinth organ...
fish, which exhibited signs of epizootic ulcerative syndrome following an outbreak of this syndrome in Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
. The new viral isolate was identified as a rhabdovirus based on images and measurements taken via transmission electron microscopy
Transmission electron microscopy
Transmission electron microscopy is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through...
and biochemical test results. Plaque neutralization tests and immunofluorescence
Immunofluorescence
Immunofluorescence is a technique used for light microscopy with a fluorescence microscope and is used primarily on biological samples. This technique uses the specificity of antibodies to their antigen to target fluorescent dyes to specific biomolecule targets within a cell, and therefore allows...
tests demonstrated that the new isolate was serologically unrelated to several other fish rhabdoviruses, including anquilla rhabdovirus (EVX), infectious hematopoietic necrosis virus
Infectious hematopoietic necrosis virus
-Introduction:Infectious hematopoietic necrosis virus , is a negative-sense single-stranded, bullet-shaped RNA virus that is a member of the Rhabdoviridae family, and from the genus Novirhabdovirus. It causes the disease known as infectious hematopoietic necrosis in salmonid fish like trout and...
(IHNV), pike fry rhabdovirus (PFRV), spring viremia of carp virus (SVCV), and viral hemorrhagic septicemia
Viral hemorrhagic septicemia
Viral hemorrhagic septicemia is a deadly infectious fish disease caused by theViral hemorrhagic septicemia virus...
virus (VHSV). Subsequent infection studies exposing healthy snakehead murrels from a susceptible population to SHNV did not develop clinical signs associated with EUS, suggesting that SHRV does not play a significant role in EUS.
Taxonomy
It is classified as a Novirhabdovirus because it possesses a nonvirion gene (NV), which is the distinguishing feature of this genus. The NV gene is situated between the glycoproteinGlycoprotein
Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...
(G) and the polymerase
Polymerase
A polymerase is an enzyme whose central function is associated with polymers of nucleic acids such as RNA and DNA.The primary function of a polymerase is the polymerization of new DNA or RNA against an existing DNA or RNA template in the processes of replication and transcription...
(L) genes, and contains a single open reading frame
Open reading frame
In molecular genetics, an open reading frame is a DNA sequence that does not contain a stop codon in a given reading frame.Normally, inserts which interrupt the reading frame of a subsequent region after the start codon cause frameshift mutation of the sequence and dislocate the sequences for stop...
(ORF), which is 335 nucleotide
Nucleotide
Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
s in length. It is called the "nonvirion" gene because no corresponding protein is present in the virion. Although the NV genes of novirhabdoviruses are similar in size, including approximately 110-122 codons, little sequence homology
Homology
Homology may refer to:* Homology , analogy between human beliefs, practices or artifacts owing to genetic or historical connections* Homology , any characteristic of biological organisms that is derived from a common ancestor....
is evident.
Coding sequences of its glycoprotein (G) genes were found to be similar to the three other presently-classified novirhabdoviruses, VHSV, IHNV, and Hirame rhabdovirus (HIRRV), with between 36% and 47% amino acid identity.
Structure
SHRV is an enveloped, bullet-shaped RNA virus measuring approximately 170 nm x 60 nm with an electron dense nucleocapsid.Genome
The SHRV 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....
is a non-segmented, negative sense RNA genome that is approximately 11,550 nucleotides in length, with six ORFs, including the matrix (M) gene, the nonvirion (NV) gene, the nucleoprotein
Nucleoprotein
A nucleoprotein is any protein that is structurally associated with nucleic acid .Many viruses harness this protein, and they are known for being host-specific...
(N) gene, the phosphoprotein
Phosphoprotein
Phosphoproteins are proteins that are physically bonded to a substance containing phosphoric acid . This category of organic molecules includes Fc receptors, Ulks, Calcineurins, K chips, and urocortins....
(P) gene, the polymerase
Polymerase
A polymerase is an enzyme whose central function is associated with polymers of nucleic acids such as RNA and DNA.The primary function of a polymerase is the polymerization of new DNA or RNA against an existing DNA or RNA template in the processes of replication and transcription...
(large protein, L) gene, and the viral glycoprotein gene (G), arranged in the following order: 3'-N-P-M-G-NV-L-5'.
Replication
Viral replication occurs at both 15°C and 28°C in cell line derived from snakehead and carpCarp
Carp are various species of oily freshwater fish of the family Cyprinidae, a very large group of fish native to Europe and Asia. The cypriniformes are traditionally grouped with the Characiformes, Siluriformes and Gymnotiformes to create the superorder Ostariophysi, since these groups have certain...
, although the optimal temperature range for viral replication is between 28°C and 31°C.
Stability
SHRV has been demonstrated to become inactivated following treatment with acidAcid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
(pH = 3), chloroform
Chloroform
Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous...
(50%), and heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
(56°C). SHRV in distilled water
Distilled water
Distilled water is water that has many of its impurities removed through distillation. Distillation involves boiling the water and then condensing the steam into a clean container.-History:...
can be completely inactivated by less than five minutes of exposure to 12.5 ppm chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
, 50 ppm iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
, or a 1:2000 dilution of peroxygen disinfectant.
Exposure of infective virions in cell culture material to 2% formalin reduced infectivity by 99.9% after 5 minutes, and completely after 30 minutes. However, exposure of infectious cell culture material to 0.025% formalin for 60 minutes caused only a negligible reduction in infectivity, and more than 50 ppm chlorine was needed to inactivate the virus Also in cell culture fluids, exposure to 500 ppm iodine for 30 minutes did not reduce infectivity. The virus does not lose infectivity when exposed in cell culture fluids to malachite green
Malachite green
Malachite green is an organic compound that is used as a dyestuff and has emerged as a controversial agent in aquaculture. Malachite green is traditionally used as a dye for materials such as silk, leather, and paper...
for 6 hours at 5 ppm.
Snakehead Infections
Infection studies with SHNV did not produce disease in exposed healthy snakehead murrels.Zebrafish Infections
The first experimental infections conducted with SHRV in zebrafish demonstrated that the NV gene played no important role in the pathogenesisPathogenesis
The pathogenesis of a disease is the mechanism by which the disease is caused. The term can also be used to describe the origin and development of the disease and whether it is acute, chronic or recurrent...
of infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
.
Subsequent experimental infections exposed zebrafish embryos, juveniles, and adults to SHRV by immersion and/or intraperitoneal (IP) injection
Injection
Injection or Injected may refer to:* Injection , insertion of liquid into the body with a syringe* Injective function in mathematics, a function mapping distinct arguments to distinct values...
. Whereas embryos and larvae were susceptible to infection by immersion, adult zebrafish were only susceptible to infection by IP injection. Histopathology
Histopathology
Histopathology refers to the microscopic examination of tissue in order to study the manifestations of disease...
of infected embryos and juvenile fish revealed vascular monocyte
Monocyte
Monocytes are a type of white blood cell and are part of the innate immune system of vertebrates including all mammals , birds, reptiles, and fish. Monocytes play multiple roles in immune function...
accumulation, accumulation of cellular debris in the gas bladder
Gas bladder
The swim bladder, gas bladder, fish maw or air bladder is an internal gas-filled organ that contributes to the ability of a fish to control its buoyancy, and thus to stay at the current water depth without having to waste energy in swimming...
, necrosis
Necrosis
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...
of hepatocytes, and necrosis of pharyngeal epithelial cells. SHRV induced interferon
Interferon
Interferons are proteins made and released by host cells in response to the presence of pathogens—such as viruses, bacteria, or parasites—or tumor cells. They allow communication between cells to trigger the protective defenses of the immune system that eradicate pathogens or tumors.IFNs belong to...
(IFN) and orthomyxovirus resistance (Mx) gene expression in zebrafish at levels dependent on route of inoculation and fish age.