A "novel" virus

By Ray Grigg, September 2013

The latest deadly threat to BC’s wild salmon.

If the research recommendations of the Cohen Commission Report are to be implemented, then the study of pathogens emanating from net-pen salmon farms would be a useful place to begin. Indeed, Justice Cohen is quite explicit that rigorous testing be undertaken on “the hypothesis that diseases are transmitted from farmed salmon” to wild species.

This is a fertile area for study. For example, Justice Cohen learned during a special reconvening of his Commission in December 2011, that infectious salmon anemia (ISAv), is a lethal viral infection in wild salmon linked to the arrival of salmon farms to BC’s West Coast. Had he chosen to reconvene again four months later at the urging of Alexandra Morton, he would also have learned of another debilitating affliction likely brought to the West Coast by the salmon farming industry. A piscine reovirus (PRV), known to cause heart and skeletal muscle inflammation (HSMI), can so weaken wild salmon that they may be unable to swim the oceans or migrate to their spawning grounds. Although Justice Cohen didn’t receive evidence on PRV-HSMI, he already knew enough from his hearings to warn that “devastating disease could sweep through wild [salmon] populations…”

Just as Justice Cohen anticipated in his Report, the presence of PRV-HSMI in BC’s wild salmon was not revealed by the provincial government or the Department of Fisheries and Oceans (DFO), the two agencies that are supposed to be monitoring the condition of marine health. Once again disclosure of PRV-HSMI came from Morton.

The credibility of her April 2012, findings were supported by Professor Rick Routledge, a Simon Fraser University fish population statistician, whose research team found the piscine reovirus in 13 of 15 Cultus Lake cutthroat trout, a salmonid species. Such a virus might explain the mysterious collapse of Cultus Lake salmon runs.

Morton also discovered PRV-HSMI when she purchased 45 BC-grown farmed Atlantic salmon from supermarkets in Vancouver and Victoria during February 2012, and sent samples to PEI’s Atlantic Veterinary Lab for testing. Of the 45 samples, 44 tested positive for the piscine reovirus known to cause HSMI. The sequenced profile of the virus indicated it was 99 percent identical to the one found in Norwegian farmed salmon. If this reovirus is in BC farmed salmon in such high proportions, it is almost certainly in the wild salmon that swim past the farms on their migration routes, providing the most likely explanation for how the virus got to Cultus Lake cutthroat.

The implications for all salmonids are significant. As Morton explains, “The obvious potential that piscine reovirus is killing Fraser sockeye by weakening their hearts, rendering them less capable of fighting their way through white water rapids like Hell’s Gate, was never raised at the [Cohen Commission] Inquiry, despite the Province of BC apparently knowing it was common in salmon farms.” 

As Morton contends, this information about PRV-HSMI is vital if we are to explain why “over 90 percent of the Fraser sockeye die as they are swimming upstream.”

 

If we are to understand how piscine reovirus has been able to infect salmon, we need to understand the genetic ingenuity of viruses. 

Many of our common human diseases, for example, have come to us from farmed animals through the “horizontal transfer” of novel genetic material that occurs in the microbial world of bacteria and viruses. Thanks to globalization and industrial agriculture, at least 30 new diseases have occurred since 1970, the most obvious being the variants of swine and bird flu.

The crowded conditions in poultry or salmon farms provide the perfect combination of density and stress that allows viruses to exchange genetic material with each other. The result can increase their virulence, allow them to infect a new species, or even create an entirely novel version of themselves—in taxonomy, a new genus. 

Which brings us to salmon and viruses.

In 1999, fish in a salmon farm in Norway began to exhibit strange symptoms. Pathologists found they were infected with a new disease later identified as heart and skeletal muscle inflammation (HSMI). Symptoms included a pale and soft heart muscle, yellowish liver, swollen spleen and other swellings. Infection rates in pens were as high as 20 percent, with morbidity close to 100 percent. 

HSMI was extremely infectious, soon spreading to 417 other salmon farms in Norway, then to facilities in the United Kingdom. Indeed, HSMI was discovered to be so infectious that it threatened wild fish that came in contact with the farms or with infected fish that escaped from them. According to Brandon Keim, writing in Wired Science in 2010, “Infected fish are physically stunted and their muscles are so weakened that they have trouble swimming or even pumping blood.”

Scientists Gustavo Palacios, W. Ian Lipkin, et al, writing in the journal PLOS One, cite evidence “that HSMI is associated with infection with piscine reovirus,” presumably the way AIDS is associated with HIV—one is a full-blown version of the other. The article claims that “PRV is a novel reovirus identified by unbiased high throughput DNA sequencing,” that “PRV is the causative agent for HSMI,” and that “measures must be taken to control PRV not only because it threatens domestic salmon production but also due to the potential for transmission to wild salmon populations.”

The clue to the origin and virulence of the PRV/HSMI virus and disease comes from the PLOS One article and the word “novel”. 

Two general kinds of the family of “Reoviridae” virus occur in the fauna community. One is an orthoreovirus, which includes both a mammalian and an avian strain. The other is an aquareovirus which is exclusive to aquatic animals. An analysis of the genetic material of the piscine reovirus identifies it as distinctly different from the two general groups, but situates it exactly between them, embodying half the attributes of the avian orthoreovirus and half the attributes of the aquareovirus. 

In other words, PRV is a new genus, designated GU994015 PRV, that has combined the traits of a bird virus and an aquatic virus—the first such amalgamation that has occurred since the divergence of the virus about 50 million years ago (Journal of General Virology, Aug 2002, and PubMed, May, 2013). This probably explains why it is so infectious.

But how did it become so “novel”?

Well, strange things can happen when salmon eat chickens. The salmon farming industry has routinely been adding chicken wastes to its salmon feed. Such a diet is unprecedented and bizarre in nature, a violation of the biological order that has occurred over millions of years of evolutionary history. Feeding chickens to salmon creates the perfect conditions for viruses to transfer genetic material horizontally from species to species. This might explain how the aquareovirus was able to exchange useful DNA with the avian orthoreovirus to develop a new virulent version of itself to infect fish, manifesting as the novel piscine reovirus and then with the clinical symptoms of HSMI.

 

When Dr Kristy Miller was giving evidence at the reconvened hearings of the Cohen Commission in December 2011, she did mention that preliminary indications—made independently by her in defiance of DFO instructions to cease investigations—identified piscine reovirus in Chinook salmon in a farm in Clayoquot Sound and in some Fraser River sockeye. Since the focus at the time was on infectious salmon anaemia (ISAv), the evidence of PRV-HSMI seemed to pass as merely incidental information.

But it wasn’t incidental information. It was and is extremely relevant, even though the presence of PRV doesn’t technically mean the clinical symptoms of HSMI are present. Reports from the provincial veterinarian pathologist lab as early as 2008 showed “congestion and hemorrhage in the stratum compactum of the heart” in farmed salmon, symptoms consistent with PRV-HSMI. And both the pathologist and the industry were aware of 75 percent infection rates of PRV in farmed salmon in 2010. Presumably this information was not conveyed to the Cohen Commission because the pathologist and industry did not think the link between PRV and HSMI was relevant, so did not consider the reovirus to be a health concern to wild salmon.

However, as Morton has pointed out in her website (and the recent film, Salmon Confidential), this opinion is contradicted by a joint scientific publication by the Center for Infection and Immunity at Columbia University and by Norwegian government scientists who warn, “It is urgent that measures be taken to control PRV not only because it threatens domestic salmon production but also due to potential for transmission to wild salmon populations.”

Justice Cohen seemed to view such warnings as real and justified, and “that salmon farms along the sockeye migration route have the potential to introduce exotic diseases and to exacerbate endemic diseases…I therefore conclude that the potential harm posed to Fraser River sockeye salmon from salmon farms is serious or irreversible”—a damning finding considering that, in his terminology, “Fraser River sockeye” usually means “all wild salmon.”

 

In May 2013, BC filmmaker Twyla Roscovich travelled to Norway and interviewed scientists there about PRV and HSMI. See her film at http://vimeo.com/70399899. Research results in BC, along with the film Salmon Confidential can be found at www.deptwildsalmon.org. Alexandra Morton reports on her research at www.alexandramorton.typepad.com.

Ray Grigg has been writing a weekly environmental newspaper column, Shades of Green, for over ten years, and is the author of seven books on Eastern philosophy. He lives on Quadra Island, BC.