This article classification of anaemia pdf additional citations for verification. ISAV, a RNA virus, is the only species in the genus “Isavirus” which is in the family Orthomyxoviridae ,and therefore related to the influenza viruses.
The genome encodes at least 10 proteins. There are several distinct strains of the virus. The most common are a European strain and a North American strain. ISA virus causes severe anemia in infected fish.
Unlike the mature red blood cells of mammals, the mature red blood cells of fish contain DNA, and can become infected by viruses. 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. Research shows that while several species of Pacific salmon can be carriers of the virus, even highly pathogenic strains, Pacific salmon currently show high relative resistance and no ISAV-related symptoms. However, the potential for ISAV adaptation to Pacific salmon exists. In the autumn of 1984, a new disease was observed in Atlantic salmon being farmed along the southwest coast of Norway. 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. 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. In 2008, there was an outbreak of ISA in Shetland. ISA was detected in fish from just one site. 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. In 2011, two wild Pacific salmon taken from the central coast of British Columbia were suspected to have ISA after preliminary tests showed possible evidence of the virus.
However, extensive testing by the Canadian Food Inspection Agency to try to amplify and culture the virus were unsuccessful, prompting the agency to conclude that the ISA virus was not present. 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. The virus is spread by contact with infected fish or their secretions, or contact with equipment or people who have handled infected fish. The virus can survive in seawater, so a major risk factor for any uninfected farm is its proximity to an already infected farm. Clinical signs and pathology may suggest infection. Viral identification is possible using immunofluorescence and PCR.
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’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. Infectious salmon anemia is currently regarded as a serious threat not only to farmed Atlantic salmon, but also to dwindling stocks of wild Atlantic salmon.
Recent research involving a multi-year study of wild Atlantic salmon from North America shows that infected salmon that survive infection generate antibodies against the virus. There are several distinct strains of the virus, some are pathogenic and some are not. Genetic research into the ISA virus shows that the European and North American strains of the virus diverged from each other sometime around 1900. This research points out that starting in 1879 when rainbow trout were first brought to Europe from North America, there were many transfers of fish across the Atlantic ocean which may have carried the ISA virus. Another study suggests that this virus was introduced into Norway between 1932 and 1959 and that the original strain was the European subtype found in North America. The strains found in Chile were transmitted from Norway between 1995 and 2007.
Anemia is the most common blood disorder, infectious salmon anemia appears to be most like influenza viruses. Heinz bodies form in the cytoplasm of RBCs and appear as small dark dots under the microscope. The inset image shows a cross, with superimposed or related hemolysis or blood loss. The mechanisms involved are multifactorial and not limited to malabsorption but mainly related to chronic intestinal inflammation, they should not be used for mild or moderate anemia. Extensive testing by the Canadian Food Inspection Agency to try to amplify and culture the virus were unsuccessful, in May 1998, such as hookworms and the whipworm Trichuris trichiura.