Around the World, Warmer Temperatures Mean More Infections

April 25, 2006 — -- At first glance, an outbreak of diarrhea among passengers on board a cruise ship in Alaskan waters in the summer of 2004 seemed to be relatively harmless.

Health officials theorized it might be the Norwalk virus, a bug that often affects people living in close quarters, such as in nursing homes, hospitals and cruise ships. While certainly annoying, Norwalk usually doesn't cause serious illness.

But then the lab reports started trickling in, and it showed that indeed a more serious problem was at hand -- many of the afflicted the passengers had eaten raw oysters raised in Alaska that were infected with a type of cholera-like bacteria, Vibrio parahaemolyticus, that normally grows on shellfish harvested in much warmer waters.

The finding not only signaled a dangerous new risk to the Alaskan seafood industry, it also highlighted how surprisingly and directly global warming can affect human health, particularly in terms of infectious diseases, experts say.

"Depending on the warming trend that unfolds in the years ahead, we have to accept that habitats will change ... new bugs can be expected to settle in. Every organism will find a niche," said epidemiology professor Colin Soskolne, of the University of Alberta in Canada. "With the tampering of the environment, we really can't predict with much certainty exactly what those changes will be."

Global warming is caused by an increase in carbon dioxide and other industrial and auto emissions, which trap heat in the atmosphere and increase air and water temperatures.

While he has personally noticed Alaska's shrinking glaciers and ice floes, global warming wasn't on the mind of Dr. Joseph McLaughlin as he investigated the cruise ship disease outbreak.

He simply wanted to know why the oysters were suddenly at risk -- before this outbreak, no seafood in Alaska had ever tested positive for Vibrio because the ocean water was simply too cold for the bacteria to multiply.

But that was no longer true: An analysis showed that Alaskan water was no longer as chilly as it once was, giving Vibrio a new home up north.