Global warming linked to shellfish eating risks

A local expert in pathogens has conceded that warming of regional ocean waters because of climate change “potentially” means more waterborne illnesses due to the Vibrio parahaemolyticus bacterium.

“I will admit to you…I am not an expert on oceanography or ecology in our waters,” Marsha Taylor, epidemiologist with the B.C. Centre for Disease Control, told the Georgia Straight by phone. “We know that temperature does impact or does have an effect on vibrio in the water, and the warmer the waters, the more vibrio we see. That’s why we tend to see our illness in the summer months, as the temperatures are increasing.”

According to the BCCDC’s British Columbia Annual Summary of Reportable Diseases, in 2010 there were 39 reported cases in B.C. of the illness caused by the pathogen, and there was an increase in the number of cases every year in the past five years. The bacterium concentrates in shellfish, especially oysters—which filter the surrounding seawater—and can cause choleralike symptoms, including diarrhea, nausea, cramps, and fever. In 2009, there were 34 cases, up from 23 in 2008 and 15 in 2007. Taylor said the number for 2011 was 42, but said the 2011 annual report will not be made ready until the end of this year, although her agency has issued a general advisory.

“I think it’s something that people should be aware of now, that there’s potential risks associated with shellfish, and we want people to take the necessary precautions to reduce that risk,” Taylor added. “That’s why we’ve put out the advisory…so people know what steps they can take, so eating from approved sources, and cooking their product to reduce the risk, and if they are going to self-harvest, only to self-harvest fish from areas that are open and safe according to Department of Fisheries and Oceans.”

Thorough cooking of shellfish, especially oysters, is the key to preventing illness. Severe illness is rare but sometimes occurs in people with depressed immune systems. Skin infections can result when an open wound is exposed to warm, brackish water. The infection usually runs its course within about three days. Most reported cases in B.C. have surfaced in and around Vancouver and southern Vancouver Island.

In July, research published in the scientific journal Nature Climate Change claimed that warming in the Baltic Sea is linked to recent spikes in vibrios infections. In some areas, according to the report, a 1 ° C increase in sea-surface temperatures almost tripled such cases.

The research group, composed of scientists from Finland, Britain, the U.S., and Spain, chose the Baltic Sea as an area of study because that body of water is “the fastest warming marine ecosystem examined so far anywhere on Earth”, according to the paper.

Because one result of climate change is an increase in precipitation, the salt content of river estuaries has decreased, providing ideal conditions for the bacteria to thrive in when water temperatures increase. The Strait of Georgia is already relatively brackish compared to the ocean waters off the west coast of Vancouver Island because of the runoff from the Fraser River and hundreds of streams flowing down the mountains into the strait.