Disease threat cited in global warming
Report predicts virulence and range will grow
The Boston Globe,June 21, 2002
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.
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.''
This story ran on page A3 of the Boston Globe on 6/21/2002.
Study: warmer climate, sicker Earth
Cross-species observations see climate/disease connection
MSNBC --June 20 — From coral reefs to rainforests, diseases are spreading among marine and land animals — including humans — and global warming appears to be a major factor, researchers reported Thursday in the journal Science. The study, said to be the first to analyze disease epidemics across entire plant and animal systems, bolsters climate models that have factored in the possibility of a warmer Earth creating a sicker planet. "What is most surprising is the fact that climate sensitive outbreaks are happening with so many different types of pathogens — viruses, bacteria, fungi, and parasites — as well as in such a wide range of hosts including corals, oysters, terrestrial plants, birds and humans," lead author Drew Harvell, a Cornell University biologist, said in a statement.
The researchers said they felt that common traits are likely linked to global warming. "Climate change is disrupting natural ecosystems in a way that is making life better for infectious diseases," stated Andrew Dobson, a Princeton University epidemiologist. "The accumulation of evidence has us extremely worried. We share diseases with some of these species. The risk for humans is going up."
CAUSES, CARRIERS TRACKED
The study tracked both causes and carriers of diseases that develop more
rapidly with slight rises in temperature. It found that as temperatures
increase, carriers are likely to spread into new areas where they could
devastate species that have not been previously exposed.
In the statement accompanying the study, the scientists cited these examples
of disease outbreaks tied to climate change:
Expanding range of disease carriers due to temperature. Honeycreepers,
forest songbirds that evolved only in Hawaii, are being decimated by malaria
from mosquitoes that have been able to range higher in elevation due to warmer
temperatures. "Today there are no native birds below 4,500 feet," said
Expanding range of carriers due to moisture. Rift Valley Fever, a deadly
viral illness spread by mosquitoes, is strongly linked to heavy rains, which
trigger mosquito explosions. "There is clear evidence that Rift Valley Fever
outbreaks are linked to El Niño years and we expect an increase in the frequency
of El Niños with climate change," stated coauthor Richard Ostfeld, a researcher
at the Institute of Ecosystem Studies in Millbrook, N.Y.
Increased susceptibility to disease. Coral reefs have become susceptible
to disease once they are stressed by warmer sea temperatures. The researchers
isolated one fungus threatening Caribbean sea fans and found that it grows
fastest at exactly the temperature at which many of the corals in the Florida
Keys start to bleach, a stress-created condition that turns coral white and can
eventually lead to die-offs.
Expanding range of carriers in winter. Warmer winter temperatures can also affect ranges of diseases and carriers. A winter warming trend in the mid-1990s allowed a parasite to spread north to Maine’s oysters, the researchers noted.
MORE STUDIES URGED
The researchers urged other experts to consider that diseases in their specialty might share a common link in global warming.
"This isn’t just a question of coral bleaching for a few marine ecologists, nor just a question of malaria for a few health officials — the number of similar increases in disease incidence is astonishing," said Ostfeld. "We don’t want to be alarmist, but we are alarmed."
The authors said they expect others to question their findings, in part because the issue of climate change and diseases has had very little monitoring and few long-term studies.
An immediate critic was Sherwood Idso, head of the Center for the Study of Carbon Dioxide and Global Change. He said the Science paper was based largely on speculation and presented "no concrete examples that these things will happen in the real world."
The authors urged the scientific community to tackle the issue head on with more research and gathering of statistics.
"We need to pay better attention to this issue in an increasingly unnatural world," stated Dobson.
MSNBC.com’s Miguel Llanos and The Associated Press contributed to this