A pesky type of bacteria called Vibrio parahaemolyticus presents a textbook example of the ways that climate change creates health risks in Alaska.
Vibrio parahaemolyticus is the world’s leading cause of seafood-related foodborne illnesses. Until recently, Alaska waters were considered too cold for the bacteria to pose a threat to fish-eaters in the state.
That changed in 2004.
That summer, 62 cruise ship passengers were sickened after eating raw oysters provided by a shellfish farm in Prince William Sound. At the time, it was North America’s northernmost known case of vibrio-caused human illness — by a vast distance. Up to then, the most northern case involving oysters had been about 600 miles to the south in British Columbia.
Every year since then, there have been a handful of cases reported to state health officials, though some cases undoubtedly go unreported, said Dr. Joe McLaughlin, Alaska’s state epidemiologist and lead author of the New England Journal of Medicine study that described the 2004 event.
In 2024, the most recent year for which data is available, there were seven reported cases, according to the Alaska Department of Health.
Vibriosis, the disease caused by Vibrio parahaemolyticus infections, is characterized by vomiting, diarrhea and similar symptoms broadly associated with what people term food poisoning.
The reported Alaska incidents in 2004 and subsequent years had common origins. “The vast majority of cases that we see nationally are food consumption of raw oysters. That’s certainly true here in Alaska,” McLaughlin said.
The link to warming conditions is also clear.
Vp, as the bacteria is known, thrives in warmer waters. It generally needs temps of 59 degrees Fahrenheit to be active, though it can survive in colder temperatures in a dormant state.
Prince William Sound, like the rest of Alaska, has been warming over the past decades, and additionally has been subjected to repeated marine heatwaves that have wreaked havoc for fisheries, birds and marine mammals.
The warming trends were apparent during the summer of 2004, when mean daily water temperatures at the shellfish farm that provided the oysters to the cruise passengers never dropped below the threshold during July and August.
Though infections are unpleasant, the presence of Vp poses only a minor health problem in Alaska. That is largely because the Alaska Department of Environmental Conservation’s food safety program responded quickly to the 2004 cruise ship case by setting up a new system that requires shellfish farmers to keep their products properly chilled.
“It requires water temperature monitoring at oyster harvest sites and rapid post-harvest cooling and temperature controls for all oysters harvested between June 15 and Sept. 15 every year,” McLaughlin said. “That’s when ocean waters warm up to concerning levels. And the plan has been highly effective in reducing outbreak.”
The department has the authority to take enforcement actions to keep farmed oysters safe. In 2018, for example, it temporarily shut down operations at two oyster-rearing operations in Southeast when outbreaks that year were traced to those sites. The farms reopened after they took corrective actions, as directed by DEC.
There have been no lab-confirmed cases in Alaska connected to seafood other than raw oysters, but that does not rule out the possibility, McLaughlin said. Elsewhere, people have gotten infected from different types of fish, he noted.
“In general, the risk for Alaskans — anybody who is not consuming raw oysters — your risk is extremely low of getting Vibrio parahaemolyticus infection. It’s not zero,” he said.
Alaska’s expanding shellfish-growing industry is taking the threat seriously.
At this year’s annual Mariculture Conference of Alaska, shellfish farm operators listened intently during a workshop on food safety.
At the event, experts from Washington state described steps to keep oysters and mussels safe, including protection of the “cold chain” distribution system and some innovations that have been used in southern regions where heat-related challenges are more entrenched.
Any vibriosis case can impact consumer perceptions about the industry, said Shannon Boldt, a biologist with the Pacific Shellfish Institute, a research and educational organization based in Olympia, Washington.
“We all know when an outbreak happens, everyone is affected,” Boldt said at the March 10 workshop.
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