Infectious hematopoietic necrosis virus

Introduction

Infectious hematopoietic necrosis virus (IHNV), is a negative-sense single-stranded, bullet-shaped RNA

RNA

Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....

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...

that is a member of the Rhabdoviridae
Rhabdoviridae
Rhabdoviruses are viruses belonging to the family Rhabdoviridae, which is in the order Mononegavirales. The name is derived from the Greek rhabdos meaning rod referring to the shape of the viral particles. Rhabdoviruses infect a broad range of hosts throughout the animal and plant kingdoms...

family, and from the genus

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...

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...

like trout

Trout

Trout is the name for a number of species of freshwater and saltwater fish belonging to the Salmoninae subfamily of the family Salmonidae. Salmon belong to the same family as trout. Most salmon species spend almost all their lives in salt water...

and salmon

Salmon

Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...

. The disease may be referred to by a number of other names such as Chinook Salmon Disease, Coleman Disease, Columbia River Sockeye Disease, Cultus Lake Virus Disease, Oregon Sockeye Disease, Sacramento River Chinook Disease and Sockeye Salmon Viral Disease. IHNV is commonly found in the Pacific Coast

Pacific Coast

A country's Pacific coast is the part of its coast bordering the Pacific Ocean.-The Americas:Countries on the western side of the Americas have a Pacific coast as their western border.* Geography of Canada* Geography of Chile* Geography of Colombia...

of Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

and the USA, and has also been found in Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

and Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

. The first reported epidemics of IHNV occurred in the United States at the Washington and the Oregon fish hatcheries during the 1950s.
IHNV is transmitted

Horizontal transmission

Horizontal transmission is the transmission of a bacterial, fungal, or viral infection between members of the same species that are not in a parent-child relationship....

following shedding of the virus

Viral shedding

Viral shedding refers to the successful reproduction, expulsion, and host-cell infection caused by virus progeny. Once replication has been completed and the host cell is exhausted of all resources in making viral progeny, the viruses may begin to leave the cell by several methods.The term is used...

in the feces

Feces

Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...

, urine

Urine

Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...

, sexual fluids, and external mucus

Mucus

In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...

and by direct contact or close contact with surrounding water. The virus gains entry into fish at the base of the fin

Fin

A fin is a surface used for stability and/or to produce lift and thrust or to steer while traveling in water, air, or other fluid media, . The first use of the word was for the limbs of fish, but has been extended to include other animal limbs and man-made devices...

s.

The disease is listed as a non-exotic disease of the EU and is therefore watched closely by the European Community Reference Laboratory for Fish Diseases

European Community Reference Laboratory for Fish Diseases

The European Community Reference Laboratory for Fish Diseases is currently located in Aarhus in Denmark at the National Veterinary Institute ....

. In order to keep track of the distribution of different IHNV genotypes a database called Fishpathogens.eu

Fishpathogens.eu

Fishpathogens.eu is a database created to store data on isolates of different fish pathogens and their sequences. The site was launched June 2009 with a database on Viral hemorrhagic septicemia virus...

has been created to store data on different fish

Fish

pathogens (including IHNV) and their sequences.

Classification

IHNV is the causal agent of Infectious Hematopoietic Necrosis (IHN) disease of fish and is a negative-sense single-stranded RNA virus. IHNV is a member of the genus

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...

Novirhabdovirus
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...

, belongs to the family of Rhabdoviridae
Rhabdoviridae
Rhabdoviruses are viruses belonging to the family Rhabdoviridae, which is in the order Mononegavirales. The name is derived from the Greek rhabdos meaning rod referring to the shape of the viral particles. Rhabdoviruses infect a broad range of hosts throughout the animal and plant kingdoms...

. The North American IHNV isolates are grouped based on the partial Glycoprotein (G) gene sequences. There are 3 major IHNV genogroups exist in North America and are designated as U, M and L for the upper, middle and lower portions of IHNV geographical range in North America. The Japanese and Korean isolates constitute new JRt (Japanese Rainbow trout) genogroup.

Virion

Virions consist of an envelope and a nucleocapsid. Virions are bullet-shaped and measure 45-100 nm in diameter; 100-430 nm in length. Surface projections are densely dispersed, distinctive spikes that cover the whole surface except for the quasi-planar end.

Genome Organization

The fish rhabdovirus, IHNV, has a bullet-shaped virion containing a non-segmented, negative-sense,
single-stranded RNA genome of approximately 11,000 nucleotides that encodes six proteins in the
following order: a nucleoprotein (N), a phosphoprotein (P), a matrix protein (M), a glycoprotein (G), a nonvirion protein (NV), and a polymerase (L).

To date,complete genome sequence has been available for only 3 IHNV isolates.

IHNV Replication Cycle

The rhabdoviral cycle of infection occurs by series of events in the following order: adsorption, penetration and uncoating, transcription, translation, replication, assembly and budding.

Transmission

Reservoirs of IHNV are clinically infected fish and covert carriers among cultured, feral or wild fish. Virus is shed via urine, sexual fluids and from external mucus, whereas kidney, spleen and other internal organs are the sites in which virus is most abundant during the course of overt infection. Insect, annelids and crustaceans can act as viral vectors. The potential for epizootics is highest at 10°C and the disease does not occur naturally above 15°C.

Clinical Signs

Clinical signs 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...

with IHNV include abdominal distension

Abdominal distension

Abdominal distension is a sensation of elevated abdominal pressure and volume. It is estimated that close to 25% of the US population has some degree of abdominal distension on a regular basis. Some describe it as belching, others claim they feel nausea and yet others say they pass excessive gas...

, bulging of the eyes, skin darkening, abnormal behavior, anemia

Anemia

Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...

and fading of the gill

Gill

A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s. Infected fish commonly hemorrhage in several areas; the mouth and behind the head, the pectoral fins, muscles near the anus

Anus

The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest,...

, and (in fry) the yolk sac

Yolk sac

The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...

. Diseased fish weaken eventually floating “belly-up” on the surface of the water.

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...

is common in the kidney

Kidney

The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

and spleen

Spleen

The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...

, and sometimes in the liver

Liver

The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

. Mortality is very high in young fish.

Some fish become covert carriers of the vrius if they survive infection.

Diagnosis

Clinical signs and history of previous outbreaks may be suggestive of IHN.

Staphylococcal agglutination, virus neutralisation (VN), indirect fluorescent antibody testing, ELISA, PCR and DNA probe technology are all techniques that can be used to confirm diagnosis. The gold standard is virus neutralisation. Alternatively, the identification of degeneration and necrosis of granular cells in the lamina propria, stratum compactum and stratum granulosum of the gastrointestinal tract on histopathology can be used to diagnose infection.

Treatment & Control

No treatment had yet proven to be effective. To prevent the disease, strict isolation, hygiene and testing procedures should be in place.

External links

European Community Reference Laboratory for Fish Diseases
Fishpathogens.eu A database on IHNV isolates and their sequences
Infectious Haematopoietic Necrosis, reviewed and published by Wikivet at http://en.wikivet.net/Infectious_Haematopoietic_Necrosis, accessed 09/09/2011.

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.