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Centre for disease control says norovirus outbreak linked to oysters has ended

DO_NOT_USE_Metro News logo DO_NOT_USE_Metro News 2018-05-12 Ainslie Cruickshank - StarMetro Vancouver

The BC Centre for Disease Control says an outbreak of norovirus linked to B.C. oysters has ended. The news comes a day after Fisheries and Oceans Canada announced new shellfish harvest closures due to toxins that can cause paralytic shellfish poisoning also known as red tide. © Jeff J Mitchell The BC Centre for Disease Control says an outbreak of norovirus linked to B.C. oysters has ended. The news comes a day after Fisheries and Oceans Canada announced new shellfish harvest closures due to toxins that can cause paralytic shellfish poisoning also known as red tide.

VANCOUVER—The BC Centre for Disease Control declared on Friday an end to the outbreak of norovirus from oysters harvested off the coast of Vancouver Island.

Since early March, more than 130 people in B.C. have fallen ill with norovirus — which causes diarrhea, vomiting and nausea — but no new cases have been reported recently, said Marsha Taylor, an epidemiologist with the centre.

The shellfish harvest in the south and central Baynes Sound area, which was linked to the outbreak, remains closed. Five harvest areas were shut down because of the norovirus investigation, including the latest closure in early May.

While the centre for disease control is still investigating the source of the contamination, Taylor previously told the Star human sewage was the most likely culprit.

“We haven’t identified a specific source of contamination,” she said Friday, though the centre is investigating commercial fishing vessels that were in the area during the herring run and may have released sewage into the water.

B.C. oysters were also linked to a norovirus outbreak in late 2016 and early 2017, during which almost 350 people fell ill in B.C., Alberta and Ontario.

On Thursday, Fisheries and Oceans Canada announced additional shellfish harvest closures, this time related to biotoxin contamination.

Shellfish in the Nootka Sound, near Quadra and Cortes islands, and in the Northern Johnstone Strait had unacceptably high levels of toxins that can cause paralytic shellfish poisoning, also known as red tide, said Elysha Gordon, a resource management biologist and the federal department’s Canadian shellfish sanitation program coordinator.

The toxins that can cause paralytic shellfish poisoning aren’t always accompanied by a red-algal bloom, Gordon cautioned.

Paralytic shellfish poisoning can cause various symptoms from tingling or numbness on the face and neck to paralysis of the respiratory muscles, which can be fatal, Fisheries and Oceans Canada explains in fisheries notice posted last summer.

Shellfish are “highly sensitive” to their environment, the notice says.

“Because they feed themselves by filtering microscopic organisms from the water, harmful bacteria, viruses and biotoxins from their surroundings can build up in their tissues and cause illness in people who consume them,” it says.

While the BC Centre for Disease Control notes that thoroughly cooking shellfish can kill norovirus, Fisheries and Oceans Canada said cooking will not destroy the toxins that cause paralytic shellfish poisoning.

Ainslie Cruickshank is a Vancouver-based reporter covering the environment. Follow her on Twitter: @ainscruickshank

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