Oyster bacteria don't usually thrive in Alaska's chilly waters.© Getty

Alaska's dramatic warming trend seems to be affecting human health. A bacterium that plagues oysters has moved some 1,000 kilometres northwards into the warming waters of Prince William Sound, causing an outbreak of diarrhoea on a 2004 Alaskan cruise.

"We had no idea that we would ever get an outbreak in Alaska," says Joseph McLaughlin, a medical epidemiologist with the state's Department of Health and Social Services in Anchorage. McLaughlin's team investigated the cruise-ship outbreak and confirmed that Vibrio parahaemolyticus in oysters was the cause.

McLaughlin says this bacterium usually plagues the more southern waters of British Columbia. It has only been seen in an Alaskan oyster once, in 1977, during an environmental survey. It has never caused documented health problems so far north before.

The team says that rising water temperatures are probably the cause of the shift to the north. Average water temperatures at the farm that provided the oysters failed to drop below 15 °C in July and August for the first time in 2004. Temperatures that summer were on average 2 °C warmer than in previous years. And the farm records show that waters in the area have been warming by about 0.21 °C per year since 1997.

Hot times

Being health workers rather than climate experts, the team says it cannot be sure that these rising temperatures are due to global warming.

But Prince William Sound, along with the rest of Alaska, is known to be heating up at a remarkable rate. Between the 1970s and early 2000s, winters in that state warmed by a startling 2-3 °C, compared with a global average of 1°C.

It wouldn't be the first time that a warming world has changed disease patterns. Paul Epstein, associate director of the Center for Health and the Global Environment at the Harvard Medical School in Boston, notes that disease-bearing ticks in Sweden are moving northwards as winters become warmer, for example.

McLaughlin and his colleagues have linked the consumption of Alaskan oysters to serious stomach trouble in 62 people last summer. 

Alaska Department of Health and Social Services, Anchorage

• References

  1. McLaughlin A., et al. N. Eng. J. Med, 353. 1463 - 1470 (2005).