2 diseases deadly to oysters found in N.B. for 1st time

Two diseases in oysters have turned up in samples taken from in Spence Cove, about five kilometres west of the Confederation Bridge, the Canadian Food Inspection Agency announced Thursday.

The discovery of multinucleate sphere unknown, known as MSX, is a first in New Brunswick, while the discovery of perkinsosis, known as dermo, is a Canadian first.

A news release from the federal agency said these diseases do not pose any risk to humans but both cause increased mortality rates in oysters.

Fisheries and Oceans Canada and the province are working with the agency to monitor the situation, the release said.

Wayne Williams of Little Shemogue Oyster Company, based in Upper Cape, described the appearance of MSX and dermo as a big unknown.

"There's no prescription. You can't do anything to save your oysters. We're at the mercy of nature right now. So let's see what happens," Williams said.

Williams has some oyster stocks near Spence Cove, but said most of his two-to-three-million oysters are in Cocagne Bay. 

MSX was discovered in Prince Edward Island over the summer so the discovery of the two diseases in New Brunswick was expected, Williams said.

"We've all been sitting on pins and needles for years waiting for this moment because we always knew it was coming."

"No surprise, but not very welcome news."

No need to stop eating oysters, scientist says

Rod Beresford, an associate professor of biology at Cape Breton University, said MSX has been seen in Bras d'Or Lake in Cape Breton since 2002.

The oyster industry has been resilient in the face of the disease, he said. Harvesters there have tried using suspended bags to grow oysters in the water, instead of regular cages that sit on the sea floor.

"It's not perfect, you know, oysters still get infected, some still die, but the mortality rate is much lower in these places."

WATCH | Biology professor on what this means for the oyster industry:

Two oyster diseases confirmed in N.B. samples

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The Canadian Food Inspection Agency says MSX and Dermo, also known as perkinsosis, were detected in samples collected in Spence Cove, near the Confederation Bridge.

Over the long-term, Beresford said scientists can work with oyster genetics to breed and grow oysters that show resistance to MSX and dermo to protect oyster stocks.

"[Oysters] have been around for 300 million years. So we're just kind of giving them a little helping hand."

If history repeats itself, the diseases will only continue to spread in the region, he said.

"We don't know how this moves around, but there's no reason to think it won't show up in other places."

Beresford said it's important for farmers to stay positive and pointed to the U.S., where both diseases have existed for far longer and have not destroyed the oyster industry.

"So if you go down to the United States and go to an oyster bar and have your feed of oysters, in all likelihood you're eating one or both of these parasites," he said.

"You shouldn't stop eating oysters."

Prevalent in U.S. oyster populations

Ryan Carnegie studies diseases in marine animals at the Virginia Institute of Marine Science at the College of William and Mary in Williamsburg. Scientists have been studying the diseases in the school's lab since the 1950s, he said.

MSX occurs all the way down the coast from Maine to Florida and does not spread directly between oysters.

"It requires some intermediate host or hosts that have never been identified," Carnegie said.

Dermo, on the other hand, covers the same ground between Maine and Florida and extends down to parts of Mexico, but is transmissible directly between oysters. It's so prevalent that in the summer, 100 per cent of oysters in the Chesapeake Bay may be infected, he said.

The impact of dermo has changed over the years, he said. In the early years it only caused about 30 per cent mortality in oysters, but by the 1980s had become more intense and killed about 70 to 80 per cent of oysters it infected.

But over time, resistance developed, and now only about 15 to 20 per cent of oysters impacted in the mid-Atlantic region end up dying from dermo.

Despite the prevalence of both diseases, scientists have little recourse other than selective breeding for resistance, Carnegie said.

"They pretty much are where they are and we live with them."

Carnegie said oyster producers in New Brunswick should be just as concerned about dermo as they have been about MSX creeping closer and closer.

"You know, [dermo] is one of our worst pathogens, and it is capable of causing significant mortality."

It's just a matter of time for oysters to develop a natural resistance to the disease, but Carnegie said solutions like the suspended oyster bags used in Cape Breton are something that should be studied.

"That's a sort of farm-based strategy that warrants attention as a possible way of mitigating the effects of these diseases," he said.