Warming ocean waters may have tainted Alaskan oysters with a bacteria that triggered four outbreaks of illness on a cruise ship among people who ate the shellfish raw, researchers reported Wednesday.
“The rising temperatures of ocean water seem to have contributed to one of the largest known outbreaks of Vibrio parahaemolyticus in the United States,” said Joseph McLaughlin of the Alaska Department of Health and Social Services, referring to the bacterium responsible for outbreak.
He and his colleagues said 62 people fell ill on four week-long cruises in July 2004. Vibrio parahaemolyticus is the most common cause of seafood-related illness in the United States.
“Alaskan waters were thought to be too cold to support” bacteria levels known to cause the illness, said the McLaughlin team. But when they tracked the outbreaks, the source turned out to be an oyster farm in Prince William Sound, 621 miles north of any previous source of tainted oysters.
Further tests showed that other oyster facilities in Alaska’s Kachemak Bay and southeast Alaska had also begun to harbor the bacteria, which is only believed to grow in oysters where water temperatures are higher than 59 F.
Water temperatures climbing since 1976
Temperature records from the area showed that the waters were more tepid than at any time in recent history. The data also showed that temperatures at the site have climbed gradually since 1976.
Based on the study in the New England Journal of Medicine, "we can’t say why ocean temperatures are rising," McLaughlin told Reuters.
But many climate experts have warned that warmer ocean waters are a likely consequence of carbon dioxide pollution, which traps heat that would normally radiate back into space.
Scientists predict that warmer temperatures will generate stronger storms and shift local climate conditions, spreading various illnesses to new regions.
“This is probably some of the best evidence to date that rising temperatures in ocean waters might contribute to the incidence of disease,” said McLaughlin, “so we’re definitely very concerned.”
The researcher said when water temperatures at oyster farms exceed 15 degrees Celsius, health officials should test for the virus, oyster nets should be moved to cooler waters, and the public should be warned to cook oysters before eating them.
As a result of the findings, nets have been moved to cooler waters. “That seems to have worked,” the researcher said.
Most of the cruise ship travelers who fell sick had eaten just one raw oyster. The bacteria took 12 to 36 hours to make them ill.
Although it is seldom fatal, people with liver disease, diabetes or immune system problems such as AIDS may die from the infection, which killed 20 people in 2004, according to the Center for Science in the Public Interest.