Alaskan seafood under the weather

CORDOVA, Alaska — Oysterman Jim Aguiar had never had to deal with the bacterium Vibrio parahaemolyticus in his 25 years working the frigid waters of Prince William Sound.

The dangerous microbe infected seafood in warmer waters, like the Gulf of Mexico. Alaska was way too cold.

But the sound was gradually warming. By summer 2004, the temperature had risen just enough to poke above the crucial 59-degree mark. Cruise-ship passengers who had eaten local oysters were soon coming down with diarrhea, cramping and vomiting — the first cases of Vibrio food poisoning in Alaska that anyone could remember.

As scientists later determined, the culprit was not just the bacterium but the warming that allowed it to proliferate.

"This was probably the best example to date of how global-climate change is changing the importation of infectious diseases," said Dr. Joe McLaughlin, acting chief of epidemiology at the Alaska Division of Public Health, who published a study on the outbreak.

The spread of human disease has become one of the most worrisome subplots in the story of global warming.

Incremental temperature changes have begun to redraw the distribution of bacteria, insects and plants, exposing new populations to diseases that they have never seen before.

A report from the World Health Organization estimated that in 2000 about 154,000 deaths around the world could be attributed to disease outbreaks and other conditions sparked by climate change.

The temperature change has been small, about 1.4 degrees Fahrenheit over the last 150 years, but it has been enough to alter disease patterns across the globe:

• In Sweden, fewer winter days below 10 degrees and more summer days above 50 degrees have encouraged the northward movement of ticks, which has coincided with an increase in cases of tick-borne encephalitis since the 1980s.

• Researchers have found that poison ivy has grown more potent and lush because of increased carbon dioxide in the atmosphere.

• In Africa, mosquitoes have been slowly inching up the slopes around Mount Kenya, bringing malaria to high villages that had never been exposed before.

"It's going to get very warm," said Andrew Githeko, a vector biologist who heads the Climate and Human Health Research Unit at the Kenya Medical Research Institute in Kisumu. "That's going to mean a huge difference to malaria."

Githeko, 49, grew up in the damp, chilly central highlands in a tiny village near the town of Karatina, about 5,700 feet above sea level. On clear days, he could see the glaciers on Mount Kenya, the second-highest peak in Africa at 17,058 feet.

When he was a child, lowland diseases such as malaria were unknown in Karatina. But perhaps 10 years ago, a smattering of cases began to appear.

He had long ago left his home to study the great plagues of Africa — Rift Valley fever, malaria, cholera and others. After the appearance of malaria in the highlands, Githeko dispatched a colleague to collect mosquito larvae in puddles and streams around Mount Kenya, some as high as 6,300 feet. Tests later identified some of the mosquitoes as Anopheles arabiensis, one of the species that carry malaria.

Githeko's findings, published in 2006, marked the highest A. arabiensis breeding site ever recorded in Kenya and was the first published report of malaria infections in the central highlands, he said.

He knew by watching Mount Kenya's gradually disappearing glaciers that his world was warming and that lowland diseases would eventually work their way higher. "But we did not expect this to happen so soon," he said.

Githeko's work has been echoed in a small number of studies around the world.

In 1996, health authorities reported a human case of tick-borne encephalitis in the Czech village of Borova Lada, elevation 3,000 feet. Until then, the Ixodes rinicus tick, which carries the disease, had never been seen above 2,600 feet.

Milan Daniel, a parasitologist at the Institute for Postgraduate Medical Education in Prague who has been studying the movement of ticks in the Czech Republic for half a century, scoured the Sumava and Krkonose mountains and found the ticks had migrated as high as 4,100 feet.

From 1961 to 2005, the mean temperature in the Krkonose Mountains had increased about 2 1/2 degrees.

"This shift of the ticks," Daniel said, "is clearly connected with climate changes."

According to a landmark U.N. report released in February, global warming has reached a point where even if greenhouse-gas emissions could be held stable, the trend would continue for centuries.

The report painted a grim picture of the future — rising sea levels, more intense storms, widespread drought.

Predicting the future of disease, however, has proved difficult because of myriad factors — many of which have little to do with global warming. Diseases move with people, they follow trade routes, they thrive in places with poor sanitation, they develop resistance to medicines, they can blossom during war or economic breakdowns.

"No one's saying global warming is the whole picture here," said Dr. Paul Epstein, associate director of the Center for Health and the Global Environment at Harvard University. "But it is playing a role. As climate changes, it's projected to play an even greater role."

The impact of global warming has not been all bad. Researchers recently found that rising temperatures have helped reduce some diseases related to cold weather. One British study found that the number of children infected with a coldlike virus known as respiratory syncytial virus has been declining with warming temperatures.

Combining meteorological data and emergency-room admission rates from 1981 to 2004, physiologist Gavin Donaldson at University College London found each increase of 1.8 degrees clipped three weeks off the end of the virus' winter season.

"A small amount of warming can go a long way, as far as changing disease-transmission dynamics," said Dr. Jonathan Patz, director of Global Environmental Health at the University of Wisconsin in Madison.

Given the gradual pace of warming, there are also some chances to adapt.

After Prince William Sound's Vibrio outbreak in 2004, the state required more oyster testing in some areas. In the past two years, there have been only four cases of Vibrio food poisoning.