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Climate change could spark spread of disease

By Anita Manning, USA TODAY

TORONTO — Will global warming bring malaria to Montana?

Place your bets.

Scientists attending a meeting here of the American Society for Microbiology won't make predictions, but they say changes in the environment are sure to have ripple effects that pose new concerns for future outbreaks of infectious diseases.

Animals and insects can change their behaviors and expand their geographic range in response to changes in the climate and other environmental influences, experts said Tuesday.

"Infectious diseases are a moving target," said microbiologist Rita Colwell of the University of Maryland. "As climate changes, so do infectious diseases."

Warmer temperatures may lure germs of the tropics further north, said microbiologist Stephen Morse of Columbia University. Yellow fever has "largely disappeared in the U.S., but I don't see any reason why warmer temperatures couldn't bring it back," he said. People in areas where malaria is common often head for higher ground during the mosquito season, he said, but as the global climate heats up, malaria could follow them up the mountainside.

Flu is a winter disease in North America, but occurs year-round in the tropics. So, Morse said, "if we get to have a more tropical climate here, we can expect influenza to circulate year-round."

Colwell says a strategy of "pre-emptive medicine" is needed, in which public-health experts consider factors that will make a disease outbreak likely, then take steps to minimize its effect.

"If we could predict the conditions conducive to a cholera epidemic, we could provide safe drinking water, vaccines, medications," she said. "We could target it, rather than taking a shotgun approach."

Terry Yates of the University of New Mexico said scientists at his university have developed a model using environmental data to predict with 94% accuracy the severity of hantavirus in humans for the coming year.

The warm, wet winters caused by El Niño produce large populations of the white-footed deer mice that carry the virus, he said, and factors such as land use, which may affect animals that compete with the deer mice for food, also play a role. Studies show the more infected mice there are, the more human infections can be expected.

Extreme weather conditions such as floods and hurricanes not only cause immediate death and injury but also can result in a spike in infectious diseases, said Joan Rose of Michigan State University. Respiratory infections, diarrhea and other diseases increase as people are forced into crowded shelters and water supplies are contaminated, she said.

Worldwide environmental degradation caused by deforestation, soil erosion, lack of sanitation and access to safe water are danger signs that suggest that "we are at greater risk than ever before of infectious diseases associated with increasing extreme weather events," Rose said.

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