INFECTIOUS SALMON ANEMIA - CHILE
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Date: 28 Jul 2011
Source: Bloomberg News [edited]
<http://www.bloomberg.com/news/2011-07-28/chile-salmon-farmer-multiexport-gains-as-virus-concern-recedes.html>
Chile Salmon Farmer Multiexport Gains as Virus Concern Recedes
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Chilean salmon farmer Multiexport Foods SA ended a 3-day losing streak today after authorities said a virus recently confirmed at one fishing center had not affected production, quelling fears of an outbreak.
A single production center, operated by producer Acuimag SA, had confirmed presence of the virus, and it is currently without any fish, Chile's fishing regulator Sernapesca said in a report posted today on its website. Acuimag Chief Executive Officer Jorge Torrejon was not immediately available to comment, an assistant said by phone.
The agency reported 22 Jul 2011 that it had detected the presence of infectious salmon anemia (ISA) virus in 23 fishing centers in southern Chile. They included one operated by Multiexport, Santiago-based brokerage Euroamerica Corredores de Bolsa wrote yesterday. An outbreak of the ISA virus decimated Chile's salmon industry in 2007.
"There have been no reports of the strand that causes mortality,"
Patricia Pellegrini, an analyst at Santiago-based brokerage firm Larrain Vial SA, said today in an e-mailed response to questions.
Salmon prices have risen in the last week, ending a downtrend, Pellegrini said.
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[Infectious salmon anemia (ISA) is one of the most important viral diseases of farmed Atlantic salmon. This highly contagious disease can be insidious, with an initially low mortality rate; however, the cumulative mortality can sometimes exceed 90 percent if the disease remains unchecked. Infectious salmon anemia was 1st described in Norway in 1984, and it continues to be a problem in that country despite control measures.
Infectious salmon anemia virus (ISAV) is a member of the genus Isavirus in the family Orthomyxoviridae. Hemorrhagic kidney syndrome is an old name for the disease in Atlantic salmon. In coho salmon, it has also been called icterus syndrome.
Outbreaks of infectious salmon anemia occur mainly in farmed Atlantic salmon (_Salmo salar_). Wild Atlantic salmon might also be susceptible. Rarely, isolates have been reported to affect other salmonids. One virus has been linked to outbreaks in coho salmon (_Oncorhyncus kisutch_) in Chile. A different ISAV isolate caused clinical signs in experimentally infected rainbow trout (_O. mykiss_).
The latter isolate was highly virulent for Atlantic salmon, but it infected coho salmon subclinically.
The reservoir hosts for ISAV are unknown. In experiments, isolates that are virulent for Atlantic salmon usually infect other fish asymptomatically. Subclinical infections with these isolates have been reported in salmonids
Horizontal transmission of ISAV occurs readily within a tank or net pen. Transmission also takes place, although more slowly, between salmon in different nets at a site, as well as between farms. ISAV probably infects fish through the gills, but ingestion has not been ruled out. This virus is shed in epidermal mucus, urine, feces and gonadal fluids. In one study, virus shedding was 1st detected 7 days after inoculation, and rose above the minimum infective dose on day 11, 2 days before the 1st deaths occurred. Shedding peaked approximately 15 days after inoculation, when mortalities were high.
ISAV also occurs in blood and tissues; tissue wastes from infected fish are infectious. ISAV replicates best at the cold temperatures where salmon thrive (5-15 deg C [41-59 deg F]). The optimal growth temperature for this virus in cell lines is 10-15 deg C (50-59 deg F); it does not replicate when the temperature is 25 deg C (77 deg F) or higher. Fish that survive the illness can shed the virus for more than a month.
Epidemiological studies suggest that ISAV can be transmitted indirectly in water and on fomites, as well as by close contact between fish. Horizontal transmission can occur in both freshwater and seawater. Sea lice (_Lepeophtheirus salmonis_ and _Caligus_ sp.) may be mechanical vectors. These parasites could also increase the susceptibility of fish by increasing stress.
In farmed Atlantic salmon, the clinical signs may include lethargy, anemia, leukopenia, ascites, exophthalmia, darkened skin and increased mortality. In some cases, the hematocrit may be nearly normal; in others, severe anemia with a hematocrit as low as 2-3 percent may be seen. As a result of the anemia, the gills may be pale. Hemorrhages may be found in the anterior chamber of the eye. Jaundice on the ventral portion of the body has been reported among Atlantic salmon in Chile.
Similar signs, including anemia and pale gills, were seen in farmed coho salmon in Chile. Jaundice, with yellowing of the base of the fins and on the abdomen, was reported in this species.
If infectious salmon anemia is detected, aggressive depopulation of the affected cages can decrease losses. Early detection by regular surveillance can improve the effectiveness of this technique, as fish can shed ISAV before the mortality rate increases. Most salmon producing countries enforce mandatory depopulation and disinfection of infected cages; however, the specific strategy may vary between countries. For example, some countries may manage infections at the cage or pen level, while others mandate depopulation of the farm.
Quarantines and movement controls are used to prevent the virus from spreading to other farms. Fallowing of infected sites helps eliminate viruses that may remain in seawater and/or marine life and fomites in the area.
Because there is still some controversy about the possibility of vertical transmission, some fish industries (including the U.S.) have adopted broodstock screening techniques for ISA. Egg disinfection, which is used to control a variety of fish diseases, would be effective against viruses transmitted on the surface of the egg.
Nonpathogenic (e.g., HPR0) isolates that can be detected only by RT-PCR do not necessarily trigger automatic disease control efforts.
The prevalence of these viruses among salmonid and non-salmonid fish, and their potential to generate virulent isolates, is still poorly understood. Their existence could mean that the complete elimination of infectious salmon anemia among sea-raised salmon might be impossible.
There is no indication that ISAV can affect humans. Because this virus is inactivated at body temperatures of 37-40 deg C (98.6-104 deg F), it is unlikely to infect any mammal or bird.
This comment has been extracted from
<http://www.cfsph.iastate.edu/Factsheets/pdfs/infectious_salmon_anemia.pdf>
- Mod.TG
The interactive HealthMap/ProMED map for Chile is available at:
<http://healthmap.org/r/00Bj> - CopyEd.EJP]
[see also:
2010
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Infectious salmon anemia - Chile 20100820.2909 Infectious salmon anemia - Chile (02): (MA) 20101109.4064
2009
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Infectious salmon anemia - Chile 20090715.2526 Infectious salmon anemia - Chile (02): origin 20090719.2568] .................................................tg/ejp/dk/ll
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