Infectious salmon anemia
Encyclopedia
Infectious salmon anemia or anaemia (ISA) is a viral
disease
of Atlantic Salmon
(Salmo salar) that affects fish farms
in Canada
, Norway
, Scotland
and Chile
, causing severe losses to infected farms. 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
.
The aetiological agent of ISA is the infectious salmon anemia virus (ISAV). ISAV, a RNA virus, is the only species in the genus "Isavirus" which is in the family Orthomyxoviridae
.
of infected fish
. Unlike mammals, the red blood cells of fish have DNA, and can become infected with viruses. The fish develop pale gill
s, and may swim close to the water surface, gulping for air. However, the disease can also develop without the fish showing any external signs of illness, the fish maintain a normal appetite, and then they suddenly die. The disease can progress slowly throughout an infected farm and, in the worst cases, death rates may approach 100%. Post-mortem examination of the fish has shown a wide range of causes of death. The liver
and spleen
may be swollen, congested or partially already dead. The circulatory system
may stop working, and the blood may be contaminated with dead blood cell
s. Red blood cells still present often burst easily and the numbers of immature and damaged blood cells are increased.
Infectious salmon anemia appears to be most like influenza
viruses. Its mode of transfer and the natural reservoirs of infectious salmon anemia virus are not fully understood. Apart from Atlantic salmon, both sea-run Brown trout
(Salmo trutta) and Rainbow trout
(Onchorhyncus mykiss) can be infected, but do not become sick, so it is thought possible that these species may act as important carriers
and reservoirs of the virus.
In the summer of 1996, a new disease appeared in Atlantic salmon being farmed in New Brunswick
, Canada. The death rate of the fish on affected farms was very high and, following extensive scientific examination of the victims, the disease was named "hemorrhagic kidney syndrome." Although the source and distribution of this disease was not known, the results of studies by Norwegian and Canadian scientists showed conclusively that the same virus was responsible for both infectious salmon anemia and hemorrhagic kidney syndrome.
In May 1998, a salmon farm
at Loch Nevis
on the west coast of Scotland reported its suspicions of an outbreak of infectious salmon anemia. The suspicions were confirmed, and by the end of the year, the disease had spread to an additional fifteen farms not only on the Scottish mainland but also on Skye and Shetland.
More recently (2008) there has been another outbreak of ISA in Shetland. ISA was detected in fish from just one site, which has since been harvested and will remain fallow. There is no evidence the disease has spread beyond this site, but two nearby SSF cages are under suspicion of carrying the disease and are also now clear of fish.
Most recently (2011) two wild pacific salmon were confirmed to have the disease off the central coast of British Columbia. According to the federal Centers for Disease Control and Prevention, infectious salmon anemia virus morphed from a benign form in nature into a “novel virulent strain” when salmon stocks entered Norway’s densely packed salmon farms. Rather than getting picked off by a predator, a sick fish would undergo a slow death in a crowded pen, shedding virus particles. See the following site for more details: http://www.nytimes.com/2011/10/18/science/18salmon.html.
In Chile
, ISA was first isolated from a salmon farm in the 1990s and described for the first time in 2001 although the initial presence never resulted in widespread problems. However, since June 2007, the national industry has been dealing with a serious ISA outbreak which has not yet been completely brought under control and has been responsible for an important decline in the industry, closure of many farms and high unemployment. The virus was detected in an Atlantic salmon farm in Chiloé Archipelago
in Los Lagos Region
and spread to the fjords and channels of Aysén Region
to the south almost immediately
More recently the sea louse, a small crustacean
parasite that attacks the protective mucous
, scales
and skin
of the salmon has been shown to carry the virus passively on its surface and in its digestive tract, although transmission of the disease by sea lice has not been demonstrated. It is not known whether the Infectious salmon anemia virus can reproduce itself in the sea louse, although this is a possibility as viruses often depend on secondary vectors for transmission like the Arboviruses such as dengue fever
, West Nile virus
, or African swine fever virus
.
and PCR.
ISA is a major threat to the viability of salmon farming and is now the first of the diseases classified on List One of the European Commission
’s fish health regime. Amongst other measures, this requires the total eradication of the entire fish stock should an outbreak of the disease be confirmed on any farm. The economic and social consequences of both the disease and the measures used to control it are thus very far reaching.
Infectious salmon anemia is currently regarded as a serious threat not only to farmed salmon, but also to dwindling stocks of wild salmon. Anecdotal evidence suggests that fish which survive the first infection become immune to the virus. Work is now underway to develop a vaccine
against ISA. A recent report suggests that the North American virus may be slightly different from the Norwegian virus. This makes it unlikely that the sudden appearance of the disease, at least in Canada, was due to the importation of infected Norwegian fish. The possibility then is that a single vaccine might only be effective in a limited area and maybe only for a limited time.
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...
disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
of Atlantic Salmon
Atlantic salmon
The Atlantic salmon is a species of fish in the family Salmonidae, which is found in the northern Atlantic Ocean and in rivers that flow into the north Atlantic and the north Pacific....
(Salmo salar) that affects fish farms
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...
in 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...
, Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
, Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
and Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
, causing severe losses to infected farms. 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 ....
.
The aetiological agent of ISA is the infectious salmon anemia virus (ISAV). ISAV, a RNA virus, is the only species in the genus "Isavirus" which is in the family Orthomyxoviridae
Orthomyxoviridae
The Orthomyxoviridae are a family of RNA viruses that includes five genera: Influenzavirus A, Influenzavirus B, Influenzavirus C, Isavirus and Thogotovirus. A sixth has recently been described...
.
Pathology
As the name implies, it causes severe anemiaAnemia
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...
of infected 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...
. Unlike mammals, the red blood cells of fish have DNA, and can become infected with viruses. The fish develop pale 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, and may swim close to the water surface, gulping for air. However, the disease can also develop without the fish showing any external signs of illness, the fish maintain a normal appetite, and then they suddenly die. The disease can progress slowly throughout an infected farm and, in the worst cases, death rates may approach 100%. Post-mortem examination of the fish has shown a wide range of causes of death. 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...
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...
may be swollen, congested or partially already dead. The circulatory system
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...
may stop working, and the blood may be contaminated with dead blood cell
Blood cell
A blood cell, also called a hematocyte, is a cell normally found in blood. In mammals, these fall into three general categories:* red blood cells — Erythrocytes* white blood cells — Leukocytes* platelets — Thrombocytes...
s. Red blood cells still present often burst easily and the numbers of immature and damaged blood cells are increased.
Infectious salmon anemia appears to be most like influenza
Influenza
Influenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals...
viruses. Its mode of transfer and the natural reservoirs of infectious salmon anemia virus are not fully understood. Apart from Atlantic salmon, both sea-run Brown trout
Brown trout
The brown trout and the sea trout are fish of the same species....
(Salmo trutta) and Rainbow trout
Rainbow trout
The rainbow trout is a species of salmonid native to tributaries of the Pacific Ocean in Asia and North America. The steelhead is a sea run rainbow trout usually returning to freshwater to spawn after 2 to 3 years at sea. In other words, rainbow trout and steelhead trout are the same species....
(Onchorhyncus mykiss) can be infected, but do not become sick, so it is thought possible that these species may act as important carriers
Asymptomatic carrier
An asymptomatic carrier is a person or other organism that has contracted an infectious disease, but who displays no symptoms. Although unaffected by the disease themselves, carriers can transmit it to others...
and reservoirs of the virus.
Prevalence
In the autumn of 1984, a new disease was observed in Atlantic salmon being farmed along the southwest coast of Norway. The disease, which was named Infectious salmon anemia, spread slowly. By June 1988 it had become sufficiently widespread and serious to require the Norwegian Ministry of Agriculture, Fisheries and Food to declare it a notifiable disease.In the summer of 1996, a new disease appeared in Atlantic salmon being farmed in New Brunswick
New Brunswick
New Brunswick is one of Canada's three Maritime provinces and is the only province in the federation that is constitutionally bilingual . The provincial capital is Fredericton and Saint John is the most populous city. Greater Moncton is the largest Census Metropolitan Area...
, Canada. The death rate of the fish on affected farms was very high and, following extensive scientific examination of the victims, the disease was named "hemorrhagic kidney syndrome." Although the source and distribution of this disease was not known, the results of studies by Norwegian and Canadian scientists showed conclusively that the same virus was responsible for both infectious salmon anemia and hemorrhagic kidney syndrome.
In May 1998, a salmon farm
Aquaculture of salmon
Salmon, along with carp, are the two most important fish groups in aquaculture. In 2007, the aquaculture of salmon and salmon trout was worth US$10.7 billion. The most commonly farmed salmon is the Atlantic salmon. Other commonly farmed fish groups include tilapia, catfish, sea bass, bream and...
at Loch Nevis
Loch Nevis
Loch Nevis is a sea loch in Lochaber on the west coast of Scotland.It runs inland from the Sound of Sleat, and is bounded by the peninsula of Knoydart to the north and North Morar to the south....
on the west coast of Scotland reported its suspicions of an outbreak of infectious salmon anemia. The suspicions were confirmed, and by the end of the year, the disease had spread to an additional fifteen farms not only on the Scottish mainland but also on Skye and Shetland.
More recently (2008) there has been another outbreak of ISA in Shetland. ISA was detected in fish from just one site, which has since been harvested and will remain fallow. There is no evidence the disease has spread beyond this site, but two nearby SSF cages are under suspicion of carrying the disease and are also now clear of fish.
Most recently (2011) two wild pacific salmon were confirmed to have the disease off the central coast of British Columbia. According to the federal Centers for Disease Control and Prevention, infectious salmon anemia virus morphed from a benign form in nature into a “novel virulent strain” when salmon stocks entered Norway’s densely packed salmon farms. Rather than getting picked off by a predator, a sick fish would undergo a slow death in a crowded pen, shedding virus particles. See the following site for more details: http://www.nytimes.com/2011/10/18/science/18salmon.html.
In Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
, ISA was first isolated from a salmon farm in the 1990s and described for the first time in 2001 although the initial presence never resulted in widespread problems. However, since June 2007, the national industry has been dealing with a serious ISA outbreak which has not yet been completely brought under control and has been responsible for an important decline in the industry, closure of many farms and high unemployment. The virus was detected in an Atlantic salmon farm in Chiloé Archipelago
Chiloé Archipelago
Chiloé Archipelago consists of several islands lying off the coast of Chile. It is separated from mainland Chile by Chacao Channel in the north, the Sea of Chiloé in the east and Gulf of Corcovado to the southeast. All of the archipelago except Desertores Islands, which are part of Palena...
in Los Lagos Region
Los Lagos Region
Los Lagos Region is one of Chile's 15 regions, which are first order administrative divisions, and comprises four provinces: Chiloé, Llanquihue, Osorno and Palena. The region contains the country's second largest island, Chiloé, and the second largest lake, Llanquihue.Its capital is Puerto Montt;...
and spread to the fjords and channels of Aysén Region
Aysen Region
The XI Aisén Region of General Carlos Ibáñez del Campo , also spelled Aysén, is one of Chile's 15 first order administrative divisions. Although the third largest in area, the region is Chile's most sparsely populated region with a population of 105,000. The capital of the region is Coihaique, the...
to the south almost immediately
Transmission
Transmission of the virus has been demonstrated to occur by contact with infected fish or their secretions. Contact with equipment or people who have handled infected fish also transmits the virus. The virus can survive in seawater and, not surprisingly, a major risk factor for any uninfected farm is its proximity to an already infected farm.More recently the sea louse, a small crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
parasite that attacks the protective mucous
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...
, scales
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
and skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
of the salmon has been shown to carry the virus passively on its surface and in its digestive tract, although transmission of the disease by sea lice has not been demonstrated. It is not known whether the Infectious salmon anemia virus can reproduce itself in the sea louse, although this is a possibility as viruses often depend on secondary vectors for transmission like the Arboviruses such as dengue fever
Dengue fever
Dengue fever , also known as breakbone fever, is an infectious tropical disease caused by the dengue virus. Symptoms include fever, headache, muscle and joint pains, and a characteristic skin rash that is similar to measles...
, West Nile virus
West Nile virus
West Nile virus is a virus of the family Flaviviridae. Part of the Japanese encephalitis antigenic complex of viruses, it is found in both tropical and temperate regions. It mainly infects birds, but is known to infect humans, horses, dogs, cats, bats, chipmunks, skunks, squirrels, domestic...
, or African swine fever virus
African swine fever virus
African swine fever virus is the causative agent of African swine fever . ASFV is a large, double-stranded DNA virus which replicates in the cytoplasm of infected cells, and is the only member of the Asfarviridae family. ASFV infects domestic pigs, warthogs and bushpigs, as well as soft ticks ,...
.
Diagnosis
Clinical signs and pathology may suggest infection. Viral identification is possible using immunofluorescenceImmunofluorescence
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...
and PCR.
Treatment and control
There is no treatment once fish are infected.ISA is a major threat to the viability of salmon farming and is now the first of the diseases classified on List One of the European Commission
European Commission
The European Commission is the executive body of the European Union. The body is responsible for proposing legislation, implementing decisions, upholding the Union's treaties and the general day-to-day running of the Union....
’s fish health regime. Amongst other measures, this requires the total eradication of the entire fish stock should an outbreak of the disease be confirmed on any farm. The economic and social consequences of both the disease and the measures used to control it are thus very far reaching.
Infectious salmon anemia is currently regarded as a serious threat not only to farmed salmon, but also to dwindling stocks of wild salmon. Anecdotal evidence suggests that fish which survive the first infection become immune to the virus. Work is now underway to develop a vaccine
Vaccine
A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins...
against ISA. A recent report suggests that the North American virus may be slightly different from the Norwegian virus. This makes it unlikely that the sudden appearance of the disease, at least in Canada, was due to the importation of infected Norwegian fish. The possibility then is that a single vaccine might only be effective in a limited area and maybe only for a limited time.