The man's illness sparked an investigation in Alaska, said Dr. Joe McLaughlin, a state epidemiologist. By early August, officials reported that a naturally occurring bacterium that historically hadn't been a problem here was contaminating oysters.

Alaska's leading health officials had thought waters here were too cold for Vibrio parahaemolyticus. But a warmer-than-normal summer in 2004 heated coastal waters, causing a bloom in the bacteria.

Health officials tested the bacterium strains found in Alaska oysters and in the sick people. They matched, strongly suggesting that the bacteria in the oysters were linked to the human illness. The investigation that started with one Nevada man grew to include more than 60 cases of confirmed or likely bacterial illness.

Four oyster farms in Prince William Sound and Southeast stopped selling bivalves, said Manny Soares, chief of the seafood section in the state Department of Environmental Conservation.

The outbreak surprised health officials.

"Nobody, even nationally, ever thought that we would ever encounter vibrio up here," Soares said. "We knew that it existed in the environment, of course, but we had done periodic testing and had never found a problem in any of the product."

The bacteria's virulence also was unexpected. The median number of oysters eaten by ill people was just one, McLaughlin said. Health officials also studied environmental (nonhuman) samples -- such as water, sediment and oysters -- in search of the bacteria. Almost three-fourths of the test results showed a vibrio strain with a gene known for causing illness in people, he said.

"It's alarming because it's the highest proportion that's ever been reported, by far," McLaughlin said.

State epidemiologists are seeking to publish results of their investigation of the outbreak in a medical journal. They're also considering a requirement that doctors and laboratories report vibrio infections to the state health department, McLaughlin said.

The state Department of Environmental Conservation also took action. Working with the U.S. Food and Drug Administration, the DEC created the state's first plan to test oysters and monitor water temperatures in search of another possible vibrio outbreak.

CLIMATE'S EFFECT

The flourish of vibrio bacteria in 2004 is an example of how climate change can spread infectious diseases, said Dr. Jim Berner, director of community health for the Alaska Native Tribal Health Consortium.

Vibrio has been more problematic farther south, where water temperatures are warmer. The bacteria needs a temperature of about 62 degrees to start multiplying, Soares said. The state DEC will require oyster farms monitored by its plan to conduct weekly water temperature tests between June 15 and Sept. 15 and daily checks if the temperature reaches 60 degrees or higher.

"That's when (vibrio) really kicks into overdrive and starts reproducing at levels that are going to cause problems," said Kristin Ryan, director of the DEC's Division of Environmental Health.

Ryan said health officials here thought it unlikely that Alaska waters would spike to those temperatures. But median summertime water temperatures at one Prince William Sound oyster farm have been climbing and exceeded 62 degrees last summer, a state health bulletin reported.

There's other evidence of a warmer Alaska. Berner and Mike Bradley, a veterinarian with the Alaska Native Tribal Health Consortium, have been writing and talking about it at presentations focusing on climate's effect on Alaska's health. Both were authors of the recent Arctic Climate Impact Assessment published by the International Arctic Council.

According to the report, the average temperature in the Arctic has climbed at about double the average of the rest of the world during the past few decades. In some places, winter temperatures are rising more quickly than summer temperatures. In Alaska and western Canada, winter temperatures have climbed 5 degrees to 7 degrees in the past 50 years, the report says.

Berner and Bradley say a warming climate could affect Alaska in many ways. Melting sea ice could free up a northern waterway for ships. Bradley said there's a concern for what these vessels might carry north in their bilge water.

Berner raised another concern: rats traveling on cargo ships.

"Rats are a time-honored way to transmit diseases to new regions and new populations, wildlife and human," he said.

Berner gave yet another possible result of climate change. Permafrost provides a barrier for lagoons holding sewage in rural parts of Alaska. If increasing temperatures cause deeper layers of permafrost to melt, contaminants from sewage lagoons might be able to travel into sources of surface water, he said.

But climate change can also affect animals, stressing some and making them prone to disease. Warming winter temperatures also might make it easier for sick animals to live through the cold months, they said. For example, a caribou infected with a bacteria called brucellosis may be able to survive the winter when it couldn't before. That means subsistence hunters would have a greater chance of killing an infected caribou and then contracting the disease themselves.

BIRDS, BUGS AND BEAVERS

The effect of rising temperatures on infectious diseases is difficult to predict, Bradley said.

"You can only speculate," he said, "because we don't know enough about all the factors involved in disease agents to say what's going to happen. You almost don't know until it happens."

One possibility, however, is what was seen last summer with vibrio: an infectious germ becoming a problem in an area where previously it hadn't thrived.

And there are organisms bigger than germs to consider. A warmer climate might allow birds to develop different migratory paths, flying farther north than before, Berner said.

Migratory patterns matter because birds are Alaska's chief exporter of diseases, Berner says. About 100 million birds flock to the Arctic, many of them waterfowl. These birds are a reservoir for avian influenza viruses, Bradley said, and can launch a chain of events that pass these diseases along to people.

Waterfowl in Alaska, for example, can exchange flu viruses with other birds. When winter arrives, they fly south, carrying these viruses with them. Many of them go to or pass through Southeast Asia, Berner said, or they fly to southern North America.

All it takes to transmit these diseases, Berner said, is for new bird species to become part of the Arctic ecosystem and then migrate south. The birds that flew from Alaska can transmit their viruses to local birds, even domestic swine populations there.

The hogs, in turn, can be infected with both bird and human strains of influenza. These strains can recombine in the swine population, possibly creating a flu strain that's very infectious in people and leading to a worldwide epidemic, Bradley explained.

Bradley and Berner said the change in bird migratory patterns also may bring West Nile virus to Alaska, one of the few states that so far hasn't had any homegrown cases of the virus in people, animals or birds.

Birds can be infected by West Nile virus, which kills some of them quickly. Other birds, however, can carrying it with them as they migrate north. A warmer climate might allow them to migrate farther north, where mosquitoes could bite the birds and pick up the virus. If temperatures are warm enough for the virus to mature inside the mosquito, the bug can pass along the virus the next time it bites, Berner and Bradley explained.

West Nile can infect people and other mammals, and Berner wondered if Alaska's large caribou population could be susceptible.

"Do the animals up here have a natural immunity, or do they have no immunity at all?" Bradley asked. "We don't know."

Birds aren't the only animals carrying diseases. Beavers carry the parasite giardia, which can cause diarrheal illness in people. As the vegetation eaten by beavers has spread farther north and west, beavers have moved too, thriving in parts of Alaska where they had not been seen before, Bradley said.

"So many things are moving north," he said, "and what are they carrying with them?"

INCREASED SURVEILLANCE

Answering that question requires more focus on climate's effect on infectious diseases, said Bradley and Berner.

"Everybody's noticing it," Berner said. "What we aren't doing is systematically recording it."

Doing surveillance means actively looking for spreading diseases, and making that happen requires a partnership between national agencies and local health facilities as well as subsistence hunters who kill animals that may carry disease, they said.

Berner gave this example: Subsistence hunters could collect samples from birds they catch and send them to a laboratory for analysis. Researchers could then monitor what diseases are circulating among the birds, whether the prevalence of disease has increased and whether they're infected with anything new.

Two state departments have started programs in search of spreading disease. Three years ago, the state Division of Public Health launched a surveillance program for West Nile virus. Every summer since, the division has asked Alaskans to look for and report dead birds of certain species that may carry the virus.

This summer, the DEC started its new plan to monitor shellfish farms for vibrio as well as close farms or issue recalls of oysters when necessary. Alaska has 37 shellfish farms. Two farms that were linked to at least two vibrio-related illnesses last summer will have to follow the new plan for at least the next three years, said Soares with the DEC. They'll have to routinely check their water temperatures and send in oyster samples for testing.

Any oyster farm linked to two or more future vibrio illnesses will have to follow the same monitoring program. The DEC is asking all other oyster farms to voluntarily check their water temperatures as the summer heats up, Ryan said.

After discovering last summer's vibrio outbreak, state health officials sent a message to the public too. People who are pregnant or have compromised immune systems should not eat raw oysters. Cooking the meat kills the vibrio bacteria.