Infectious salmon anemia virus spread from Norway to Chile

The Chilean salmon farming industry has been severely affected by disease caused by infectious salmon anemia virus. Salmon eggs shipped from Norway to Chile in 2007 are the cause of the outbreak (New York Times):

A virus that has killed millions of salmon in Chile and ravaged the fish farming industry there was probably brought over from Norway, a major salmon producer has acknowledged.

Infection salmon anemia virus is a member of the orthomyxovirus family, which also includes influenza virus. The virus causes disease in Atlantic salmon and has caused economic losses on fish farms in Canada, Norway, Scotland and Chile. We discussed the virus on This Week in Virology #41: Fish flu.

Reovirus infection of farmed salmon

Global fish farming may be the solution to the impending collapse of the commercial fishing industry, but penned fish are susceptible to infectious diseases. Infection with salmon infectious anemia virus, an orthomyxovirus, lead Wal-Mart to stop buying farmed salmon from Chile, the world’s second largest producer of the fish. As a consequence Chilean farmed salmon are being immunized to prevent infection. Heart and skeletal muscle inflammation (HSMI) is another disease of farmed salmon, first detected in Norway – the world’s largest supplier of the fish – in 1999. The results of deep sequencing suggest that HSMI is caused by a novel piscine reovirus.

HSMI was transmitted to salmon by inoculation with tissue extracts of diseased fish or by co-habitation. RNA was extracted from the heart and subjected to high throughput sequence analysis, which revealed the presence of a novel member of the reovirus family. These are are non-enveloped, icosahedral viruses with 10-12 segments of double-stranded RNA that infect a variety of hosts, including humans: rotaviruses are important agents of gastroenteritis.

The presence of piscine reovirus in salmon with HSMI was examined by polymerase chain reaction assays. Included were heart and kidney samples from 29 salmon from three different outbreaks of HSMI, and from 10 healthy fish. All but one of the diseased fish, and none of the healthy fish, contained PRV nucleic acid. To determine the prevalence of PRV in healthy salmon, samples were collected from 9 different Norwegian coastal waters. Sixteen of 66 (24.2%) of these fish were positive for PRV.

Is heart and skeletal muscle inflammation of salmon caused by piscine reovirus? It’s possible, but further work is needed to prove causality, as the authors write:

Formal implication of PRV in HSMI will require isolation in cell culture and fulfillment of Koch’s postulates, or prevention or modification of disease through use of specific drugs or vaccines.

It’s important to identify the etiologic agent of HSMI because it is a threat to both farmed and wild salmon. Farmed fish are kept in pens in the open ocean, facilitating spread of infectious diseases to wild fish. Knowledge of the causative agent will permit preventive measures such as immunization.

Palacios G, Lovoll M, Tengs T, Hornig M, Hutchison S, Hui J, Kongtorp RT, Savji N, Bussetti AV, Solovyov A, Kristoffersen AB, Celone C, Street C, Trifonov V, Hirschberg DL, Rabadan R, Egholm M, Rimstad E, & Lipkin WI (2010). Heart and skeletal muscle inflammation of farmed salmon is associated with infection with a novel reovirus. PloS one, 5 (7) PMID: 20634888


twiv-200Hosts: Vincent Racaniello, Dick Despommier, and Alan Dove

On episode #52 of the podcast “This Week in Virology”, Vincent, Dick, and Alan (with a cameo appearance by Rich Condit) review the world’s largest Phase III study of a complex HIV vaccine candidate in Thailand, immunization of salmon against infectious salmon anemia virus, and an outbreak of blueberry shock virus in Michigan.

Click the arrow above to play, or right-click to download TWiV #51 (60 MB .mp3, 84 minutes)

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Links for this episode:
HIV vaccine shows promise for the first time – description of the program, FDA background document (pdf), NEJM review on why AIDS vaccine is difficult (pdf), and arguments for the trial
Chile immunizes salmon (USGS article on the virus, pdf)
Blueberry virus strikes Michigan research center (information on the disease and the virus)
Rotavirus seasonality (thanks Didier!)
Viruses and the tree of life at virology blog
Big brains have evolved twice (thanks Arsen!)

Weekly Science Picks
Alan Bat Rabies and Other Lyssavirus Infections
Dick Boosting Vaccines: The Power of Adjuvants (Scientific American; subscription required)
Vincent The Ig Nobel Prizes by Marc Abrahams

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