Day: March 26, 2026

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, in the Southcentral part of the state. 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 15 degrees Celsius, or 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 15-degree Celsius 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 September 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 Alaska when outbreaks that year were traced to those sites. The farms reopened after they took corrective actions, as directed by DEC. The department also worked with the organizations distributing and serving the oysters to reinforce safety standards.

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.

She recommended that operators be forthcoming with customers as well as employees about steps to avoid Vp infection risks.

“I know it’s a little scary for growers to talk about bacteria,” she said. But it is important, she said. “It goes a long way in boosting confidence that people know what you’re doing.”

The growth of shellfish farming in Alaska is itself another link between vibrio and climate change.

As warming temperatures and ocean acidification put pressure on established fisheries and fishing-dependent communities, Alaskans have turned to mariculture as an adaptation. Governments from the federal to tribal levels and nonprofit organizations have encouraged farming of oysters, blue mussels and kelp as ways to diversify and strengthen what is commonly called the “blue economy.” The term refers to the sustainable use of marine resources.

Farmed oyster production increased from 4.5 million in 2000 to 7 million in 2022, according to the National Oceanic and Atmospheric Administration, though most of the oysters were sold within the industry rather than to the public. Each year since at least 2019, applications for new aquaculture permits have been fielded by the Alaska Department of Natural Resources, which manages state tidal and submerged lands where such activities operate. And research is underway to expand shellfish growing beyond the oysters and mussels that are currently sold, including projects exploring abalone farming and hatchery enhancement of natural clam beds.

Alaska shellfish and kelp farmer and state officials have long-term ambitions of expanding the mariculture in the state into a $100 million-a-year industry, an exponental increase from current revenues, reported at about $1.5 million in 2024.

McLaughlin said it is logical to assume that as more oysters become available on the market, the chances for vibriosis will increase.

“Fortunately, this DEC program, the control plan, the Vibrio parahaemolyticus program, has been really successful in curbing cases,” he said.

While oyster-eating people are largely protected by the Alaska Department of Environmental Conservation protocols, the same is not true for other voracious consumers of raw shellfish: sea otters.

Otters can be sentinels of ocean conditions, and studies by veterinarians in California and Alaska have used tests of otters to trace the movement of Vp through the environment.

“Sea otters likely acquire the bacteria through their local prey, their natural food source, which include filter feeders that can concentrate bacteria,” Dr. Carrie Goetz of the Alaska SeaLife Center in Seward, a coauthor of the studies, said by email.

A 2013 study led by Goetz found Vb not only in sea otters but in a harbor porpoise and a beluga whale, with infection cases coming from Homer, Seward, Cordova, Cook Inlet, Kachemak Bay, Kodiak and Dillingham — well beyond the initial geographic scope identified in 2004.

More recently, Goetz and her colleagues have been using genetic analysis to examine the virulence of Vb strains that affect sea otters, which vary a lot, they discovered. Some are apparently mild. Most of the Vb-positive otters they examined during their research were actually asymptomatic, Goetz said.

In a study published in December, the veterinarian team found signs that the most virulent strains — those causing sickness among people as well as otters — appear to be spreading geographically.

The study contains a warning for Alaska: As warming continues and marine heatwaves become more common, those virulent strains could become more dominant, posing more risks to otters and humans.

This article was produced as a project for USC Annenberg’s Center for Health Journalism and Center for Climate Journalism and Communication 2025 Health and Climate Change Reporting Fellowship.

SUBSCRIBE: GET THE MORNING HEADLINES DELIVERED TO YOUR INBOX