Case of disease that can be deadly to oysters confirmed in Nova Scotia

A disease that can kill oysters but poses no health risk to humans has been detected for the first time in Nova Scotia.

Dermo is caused by a parasite known as Perkinsus marinus and is one of two diseases impacting oysters in the Maritimes, the other being a multinucleate sphere unknown, or MSX, which was discovered in P.E.I. this past summer and previously wiped out oyster production in the Bras d'Or Lake. 

The Canadian Food Inspection Agency (CFIA) said on Wednesday in a joint statement with Nova Scotia's Department of Fisheries and Aquaculture that dermo was detected in oysters samples from Merigomish in Pictou County.

"Dermo does not pose a risk to human health or food safety, but it can cause increased oyster mortality and decreased growth rates," the statement said. 

It said officials will be working with producers, harvesters and partners, including Indigenous communities, "to monitor the situation and take necessary action" to limit the spread of the disease.

They are also "applying movement controls" to oysters from Merigomish, investigating further and looking closely at mollusc health.

2nd case in Canada

This is the second case in Canada after dermo was confirmed in New Brunswick last week.

According to the CFIA's website, dermo is highly infectious among other oysters and can be easily transmitted to oysters between one to three years of age. Dermo mortality rates in oysters can vary but are typically 50 to 70 per cent. 

Rod Beresford, an associate professor at Cape Breton University's biology department, told Radio-Canada that it's too early to know how the parasite will impact the province's oyster industry. 

"It's not good news, but the fact that we don't know how long it's been there — and it's my understanding there's not been significant mortality yet from dermo — that's probably a good sign for now," he said. 

Much of the spread of the diseases impacting oysters can likely be linked to climate change, Beresford said.

"If the waters are too cold for them to survive, they won't be a problem," he said.

"But water temperatures are warming for sure, which is going to mean that we're likely to see increases of these diseases and other diseases." 

Beresford said while oyster farmers will have to keep a close eye on their sites and products, Canadian consumers can be reassured that they are still safe to eat. 

"It's really important to recognize just how important this industry is to the entire region. This is a big economic driver, especially in rural Atlantic Canada," said Beresford.

"So if you enjoy oysters, I think people should continue to enjoy them and feel safe about eating them."