Warming temperatures around the world are increasing the geographical range
and virulence of diseases, a trend that could mean more devastating epidemics
in humans, animals, and plants, according to a report published in the magazine
Science yesterday.
The report
notes that many regions, including New England, could be losing one of their best
defenses against disease: cold weather.
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Already, the dengue virus in Latin America and Rift Valley fever in the Middle
East, which can cause people to vomit blood, have expanded their deadly range.
Meanwhile, an oyster disease has gained a foothold in Maine waters, the report
said.
Researchers have long accepted that global warming will affect a wide range
of organisms, but they are only now beginning to predict what those will be. While
climate change scientists have studied a handful of human diseases, yesterday's
report was the first to study dozens of diseases in both humans and nonhumans.
''We are seeing lots of anecdotes and they are beginning to tell a story,''
said Andrew P. Dobson, professor at Princeton University's department of ecology
and evolutionary biology and one of the authors. ''It's a much more scary threat
than bioterrorism.''
The report comes at a crucial time. Earlier this month, the Bush administration
concluded that manmade sources of heat-trapping, or greenhouse, gases were responsible
for global warming. Yesterday's report adds to the growing evidence that nearly
every part of the natural world could suffer in some way from the long-term warming
trend.
The report notes that many regions, including New England, could be losing
one of their best defenses against disease: cold weather. Every fall, mosquitoes
that may be carrying the deadly West Nile virus, for example, are killed off before
they multiply and spread the disease too widely. But as global warming heats up
the Earth, even by minute degrees, disease-carrying organisms may regenerate faster
or go into new areas where populations may have little or no natural resistance.
''It's possible that the time that it takes for [a disease-carrying organism]
population to double might be halved with a single degree or half degree of warming,''
said Rick Ostfeld, an animal ecologist at the Institute of Ecosystem Studies in
Millbrook, N.Y., one of authors. ''What we found were striking patterns of climate
warming and spread of disease, and greater incidence of disease.''
The report notes that with increased temperature, mosquitoes that carry the
dengue virus bite more often. Slime mold grows faster on eelgrass. Parasites that
attach to butterflies gather in greater density.
Not everyone will consider the news bad, however. A fungus in frogs decreases
with higher temperatures. An avian cholera that favors cold weather could disappear.
Of course, not all disease spread can be attributed to climate change. Authors
say many other reasons can account for it, including increased human travel and
resistant bugs.
Still, the spread of Rift Valley fever and even eastern oyster disease appears
to be largely related to long-term temperature fluctuations. Rift Valley, a particularly
nasty disease that can make victims go blind and vomit blood, spread across the
Red Sea in 2000 and killed 200 people in Yemen and Saudi Arabia; and its range
is expanding. Eastern oyster disease is now found in Maine waters that have warmed
slightly in recent years.
''The disease is normally limited by cold winters,'' said C. Drew Harvell,
lead author of the report and a Cornell professor in the department of ecology
and evolutionary biology. She said the virus was in Long Island and then jumped
to Maine.
''While there are multiple reasons for the redistribution of emerging disease
... it's clear there is an emerging pattern here,'' said Paul Epstein, associate
director of Harvard Medical School's Center for Health and the Global Environment.
''We've clearly underestimated the rate at which climate would change, and we
have underestimated the response to ecological systems to that warming.''
© Copyright 2002 Globe Newspaper Company
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